Without visual references, nonpilots exposed to coordinated flight turns underestimate the bank angle, because of discordant information of the roll-angular displacement from the otoliths, consistently signaling vertical position, versus the semicircular canals, enabling detection of the displacement. Pilots may also use their ability to perceive the G load and knowledge of the relation between load and angle to assess the bank angle. Our aim was to investigate whether the perception of bank angle can be improved by spatial orientation training in a centrifuge. Sixteen pilots/pilot students assessed their roll tilt, in complete darkness, during both real coordinated flight turns and gondola centrifugation, at roll tilts of 30◦ and 60◦. The experiments were repeated after a 3-wk period, during which eight of the subjects performed nine training sessions in the centrifuge, comprising feedback on roll angle vs. G load, and on indicating requested angles. Before training, the subjects perceived in the aircraft and centrifuge, respectively: 37 (17)◦, 38 (14)◦ during 60◦ turns and 19 (12)◦, 20 (10)◦ during 30◦ turns. Training improved the perception of angle during the 60◦ [to 60 (7)◦, 55 (10)◦; P ≤ 0.04] but not the 30◦ [21 (10)◦, 15 (9)◦; P ≥ 0.30] turns; the improvement disappeared within 2 yr after training. Angle assessments did not change in the untrained group. The results suggest that it is possible to, in a centrifuge, train a pilot’s ability to perceive large but not discrete-to-moderate roll-angular displacements. The transient training effect is attributable to improved capacity to perceive and translate G load into roll angle and/or to increased reliance on semicircular canal signals. NEW & NOTEWORTHY Spatial disorientation is a major problem in aviation. When performing coordinated flight turns without external visual cues (e.g., flying in clouds or darkness), the pilot underestimates the aircraft bank angle because the vestibular system provides unreliable information of roll tilt. The present study demonstrates that it is possible to, in a long-arm centrifuge, train a pilot’s ability to perceive large but not discrete-to-moderate roll-angular displacements.

BACKGROUND: Ischemic hypoxia induced by suprathreshold G-force loading can adversely affect vision, cognition, and lead to loss of consciousness (LOC). The purpose of this study was to determine whether reductions in cerebral oxygenation, caused by subthreshold G-forces (up to 4 G_z and of limited durations that do not lead to LOC), would affect visual perception and working memory performance.METHODS: Sixteen subjects performed visual perception and working memory tasks both before and during G_z exposures (1, 2.2, 3, 4 with leg pressurization, 4 with leg and abdomen pressurization) within a human-use centrifuge.RESULTS: As measured using near-infrared spectroscopy, blood oxygenation over medial prefrontal cortex was similar in the 1 and 2.2 G_z conditions, but was reduced to a similar extent in the 3 and 4 G_z conditions. In parallel, visual perception accuracy was reduced in the 3 and 4 G_z conditions, with no difference between the 3 and 4 G_z conditions. No change in reaction time was seen. Conversely, neither accuracy nor reaction time changes were observed for the visual working memory task.DISCUSSION: These results indicate that although visual working memory is not affected, the ability to visually discriminate between stimuli is reduced at G-forces as low as 3 and 4 G_z. This may have important ramifications for pilots who are routinely subjected to such forces.

Poor musculoskeletal state is commonly observed in numerous clinical populations such as chronic obstructive pulmonary disease (COPD) and heart failure patients. It, however, remains unresolved whether systemic hypoxemia, typically associated with such clinical conditions, directly contributes to muscle deterioration. We aimed to experimentally elucidate the effects of systemic environmental hypoxia upon inactivity-related muscle wasting. For this purpose, fourteen healthy, male participants underwent three 21-day long interventions in a randomized, cross-over designed manner: (i) bed rest in normoxia (NBR; PiO2 = 133.1 ± 0.3 mmHg), (ii) bed rest in normobaric hypoxia (HBR; PiO2 = 90.0 ± 0.4 mmHg) and ambulatory confinement in normobaric hypoxia (HAmb; PiO2 = 90.0 ± 0.4 mmHg). Peripheral quantitative computed tomography and vastus lateralis muscle biopsies were performed before and after the interventions to obtain thigh and calf muscle cross-sectional areas and muscle fiber phenotype changes, respectively. A significant reduction of thigh muscle size following NBR (-6.9%, SE 0.8%; P < 0.001) was further aggravated following HBR (-9.7%, SE 1.2%; P = 0.027). Bed rest-induced muscle wasting in the calf was, by contrast, not exacerbated by hypoxic conditions (P = 0.47). Reductions in both thigh (-2.7%, SE 1.1%, P = 0.017) and calf (-3.3%, SE 0.7%, P < 0.001) muscle size were noted following HAmb. A significant and comparable increase in type 2× fiber percentage of the vastus lateralis muscle was noted following both bed rest interventions (NBR = +3.1%, SE 2.6%, HBR = +3.9%, SE 2.7%, P < 0.05). Collectively, these data indicate that hypoxia can exacerbate inactivity-related muscle wasting in healthy active participants and moreover suggest that the combination of both, hypoxemia and lack of activity, as seen in COPD patients, might be particularly harmful for muscle tissue.

PURPOSE: Military parachute operations are often executed at high altitude, from an unpressurized aircraft compartment. Parachute jumpmasters (JM) are thus regularly exposed to 29,500 ft for 60 min. The aim was to investigate the decompression strain during a simulated JM mission at high altitude and to compare two strategies of preoxygenation, conducted either at sea-level or below 10,000 ft, during ascent to mission altitude.

METHODS: Ten JM completed, on separate occasions, a 45-min preoxygenation either at sea-level (normobaric: N) or 8200ft (hypobaric: H), followed by exposure to 28,000 ft for 60 min, whilst laying supine and breathing 100% oxygen. At min 45 of the exposure to 28,000 ft, the JM performed 10 weighted squats. Decompression strain was determined from ultrasound assessment of venous gas emboli (VGE) during supine rest (5-min intervals), after three unloaded knee-bends (15-min intervals) and immediately following the weighted squats. The VGE were scored using a six-graded scale (0-5).

RESULTS: In condition H, two JM experienced decompression sickness (DCS), whereas no DCS incidents were reported in condition N. The prevalence of VGE was higher in the H than the N condition, at rest [median(range), 3(0-4) vs 0(0-3); p = 0.017], after unloaded knee-bends [3(0-4) vs 0(0-3); p = 0.014] and after the 10 weighted squats [3(0-4) vs 0(0-3); p = 0.014]. VGE were detected earlier in the H (28 ± 20 min, p = 0.018) than the N condition (50 ± 19 min).

CONCLUSIONS: A preoxygenation/altitude procedure commonly used by JM, with a 60-min exposure to 28,000 ft after pre-oxygenation for 45 min at 8200 ft is associated with high risk of DCS. The decompression strain can be reduced by preoxygenating at sea level.

The aims were to study effects of iterative exposures to moderate elevations of local intravascular pressure on arterial/arteriolar stiffness and plasma levels of vasoactive substances. Pressures in the vasculature of an arm were increased by 150mmHg in healthy men (n = 11) before and after a 5-wk regimen, during which the vasculature in one arm was exposed to fifteen 40-min sessions of moderately increased transmural pressure (+65 to +105 mmHg). This vascular pressure training and the pressuredistension determinations were conducted by exposing the subjects' arm versus remaining part of the body to differential ambient pressure. During the pressure-distension determinations, venous samples were simultaneously obtained from pressurized and unpressurized vessels. Pressure training reduced arterial pressure distension by 40 ± 23% and pressure-induced flow by 33 ± 30% (P < 0.01), but only in the pressure-trained arm, suggesting local adaptive mechanisms. The distending pressure-diameter and distending pressure-flow curves, with training-induced increments in pressure thresholds and reductions in response gains, suggest that the increased precapillary stiffness was attributable to increased contractility and structural remodeling of the walls. Acute vascular pressure provocation induced local release of angiotensin-II (ANG II) and endothelin-1 (ET-1) (P < 0.05), suggesting that these vasoconstrictors limited the pressure distension. Pressure training increased basal levels of ET-1 and induced local pressure release of matrix metalloproteinase 7 (P < 0.05), suggesting involvement of these substances in vascular remodeling. The findings are compatible with the notion that local intravascular pressure load acts as a prime mover in the development of primary hypertension. 

Despite decades of experience from high-G exposures in aircraft and centrifuges, information is scarce regarding primary cardiovascular adaptations to +Gz loads in relaxed humans. Thus, effects of G-training are typically evaluated after regimens that are confounded by concomitant use of anti-G straining maneuvers, anti-G suits and pressure breathing. Accordingly, the aim was to evaluate cardiovascular adaptations to repeated +Gz exposures in the relaxed state. Eleven men underwent 5 weeks of centrifuge G training, consisting of 15 × 40 min +Gz exposures at G levels close to their individual relaxed G-level tolerance. Before and after the training regimen, relaxed G-level tolerance was investigated during rapid (ROR) and gradual (GOR) onset-rate G exposures, and cardiovascular responses were investigated during orthostatic provocation and vascular pressure-distension tests. The G training resulted in: (i) a 13% increase in relaxed ROR G tolerance (P < 0.001), but no change in GOR G tolerance, (ii) increased pressure resistance in the arteries and arterioles of the legs (P < 0.001), but not the arms, (iii) a reduced initial drop in arterial pressure upon ROR high G, but no change in arterial pressure under basal resting conditions or during GOR G loading, or orthostatic provocation. The results suggest +Gz adaptation via enhanced pressure resistance in dependent arteries/arterioles. Presumably this reflects local adaptations to high transmural pressures, resulting from the +Gz-induced exaggeration of the intravascular hydrostatic pressure gradients.

NEW FINDINGS: What is the central question of this study? Is performing a 30-min whole-body vibration (WBV) prior to a continuous 90-min exposure at 24,000 ft sufficient to prevent venous gas emboli (VGE) formation? What is the main finding and its importance? WBV preconditioning significantly reduces the formation and delays the manifestation of high-altitude-induced VGE. This study suggests that WBV is an effective strategy in lowering decompression stress.

ABSTRACT: Rapid decompression may give rise to formation of venous gas emboli (VGE) and resultantly, increase the risk of sustaining decompression sickness. Preconditioning aims at lowering the prevalence of VGE during decompression. The purpose of this study was to investigate the efficacy of whole-body vibration (WBV) preconditioning on high-altitude-induced VGE. Eight male subjects performed, on separate days in a randomised order, three preconditioning strategies: 40-min seated-rest (control), 30-min seated-rest followed by 150 knee-squats performed over a 10-min period (exercise) and 30-min WBV proceeded by a 10-min seated-rest. Thereafter, subjects were exposed to an altitude of 24,000 ft (7315 m) for 90 min whilst laying in a supine position and breathing 100% oxygen. VGE were assessed ultrasonically both during supine rest (5-min intervals) and after three fast, unloaded knee-bends (15-min intervals) and were scored using a 5-grade scale and evaluated using the Kisman Integrated Severity Score (KISS). There was a significant difference in VGE grade (P < 0.001), time to VGE manifestation (P = 0.014) and KISS score following knee-bends (P = 0.002) across protocols, with a trend in KISS score during supine rest (P = 0.070). WBV resulted in lower VGE grades (median (range), 1 (0-3)) and KISS score (2.69 ± 4.56 a.u.) compared with control (2 (1-3), P = 0.002; 12.86 ± 8.40 a.u., P = 0.011) and exercise (3 (2-4) , P < 0.001; 22.04 ± 13.45 a.u., P = 0.002). VGE were detected earlier during control (15 ± 14 min, P = 0.024) and exercise (17 ± 24 min, P = 0.032) than WBV (54 ± 38 min). Performing a 30-min WBV prior to a 90-min continuous exposure at 24,000 ft both delays the manifestation and reduces the formation of VGE compared with control and exercise preconditioning.

Breath-hold diving is an activity that humans have engaged in since antiquity to forage for resources, provide sustenance and to support military campaigns. In modern times, breath-hold diving continues to gain popularity and recognition as both a competitive and recreational sport. The continued progression of world records is somewhat remarkable, particularly given the extreme hypoxaemic and hypercapnic conditions, and hydrostatic pressures these athletes endure. However, there is abundant literature to suggest a large inter-individual variation in the apnoeic capabilities that is thus far not fully understood. In this review, we explore developments in apnoea physiology and delineate the traits and mechanisms that potentially underpin this variation. In addition, we sought to highlight the physiological (mal)adaptations associated with consistent breath-hold training. Breath-hold divers (BHDs) are evidenced to exhibit a more pronounced diving-response than non-divers, while elite BHDs (EBHDs) also display beneficial adaptations in both blood and skeletal muscle. Importantly, these physiological characteristics are documented to be primarily influenced by training-induced stimuli. BHDs are exposed to unique physiological and environmental stressors, and as such possess an ability to withstand acute cerebrovascular and neuronal strains. Whether these characteristics are also a result of training-induced adaptations or genetic predisposition is less certain. Although the long-term effects of regular breath-hold diving activity are yet to be holistically established, preliminary evidence has posed considerations for cognitive, neurological, renal and bone health in BHDs. These areas should be explored further in longitudinal studies to more confidently ascertain the long-term health implications of extreme breath-holding activity. 

Static apneas performed after an overnight fast as opposed to postprandially have been evinced to improve apneic performance. However, no study has explored the effect of dietary intake on apneic performance, cardiovascular or splenic responses over a series of repeated apneas. Ten healthy adults attended the laboratory on three separate occasions (>48-h apart): after a 14-h fast (F14), 1 h postconsumption of a high-calorie, high-carbohydrate (HCHC) meal, or 1 h postconsumption of a low-calorie, low-carbohydrate (LCLC)-based meal. During each visit, the subjects performed a hyperoxic rebreathing trial and a series of three repeated maximal static apneas. Heart rate, peripheral oxyhemoglobin saturation (Sp(O2)), and gas exchange were monitored continuously, whereas splenic volume (SV) and hematology were assessed after the rebreathing and apneas. At rest, after HCHC, the respiratory exchange ratio (0.87 +/- 0.17, P < 0.043), expired minute volume of carbon dioxide (CO2; HCHC, 0.35 +/- 0.09 L/min, P < 0.014), and SV (227 +/- 45 mL, P < 0.031) were higher compared with F14 (0.71 +/- 0.08; 0.23 +/- 0.04 L/min; 204 +/- 49 mL) and LCLC (0.72 +/- 0.07; 0.25 +/- 0.03 L/min; 199 +/- 49 mL). A faster CO2 accumulation was recorded during the HCHC (96 +/- 35 s) rebreathing trial (F14, 162 +/- 42 s, P = 0.001; LCLC, 151 +/- 23 s, P = 0.002). Longer apneas were reported in F14 compared with HCHC (apneas 1-3, P < 0.046) and LCLC (apneas 2-3, P < 0.006). After the first apnea, SV was lower in F14 (141 +/- 43 mL, P = 0.015) compared with HCHC (180 +/- 34 mL). Moreover, after the third apnea, end-tidal partial pressure of oxygen and nadir Spo t were lower in F14 (8.6 +/- 2.2 kPa, P = 0.028; 77 +/- 13%, P = 0.009) compared with HCHC (10.1 +/- 1.7 kPa; 84 +/- 9%). No differences were measured in end-apneic end-tidal partial pressure of CO2, heart rate nor hematology across diets. Fasting improved apneic performance with apneas being terminated at lower oxygen levels through altering the rate of CO2 accumulation but without affecting the cardiovascular responses.

INTRODUCTION: This study aimed to evaluate whether a short familiarization session is sufficient for individuals with no prior experience of sonography to both reliably and consistently evaluate the prevalence of venous gas emboli (VGE) from precordial ultrasonic videos.METHODS: A total of 10 adults with no prior experience of sonography were introduced to the Eftedal-Brubakk 6-grade scale and were shown 6 video sequences, each of a maximum of 10 heartbeats, representing each grading level. Thereafter, they independently evaluated the prevalence of VGE in 70 ultrasonic videos before and after a 14-d interval (test-retest; intra-rater), with these being compared to an experienced sonographer's grading (inter-rater).RESULTS: A significant inter-rater level of agreement was found between the naïve and experienced sonographers' bubble grading both during the first (W = 0.945) and second (W = 0.952) round of bubble evaluation. The naïve observers' evaluations were on average 79% (range: 61-95%) and 75% (range: 48-95%) in complete agreement with the experienced sonographer's gradings, while the level of agreement was 99% and 98% within 1 grade unit. There was a significant intra-rater level of agreement (κ = 0.845) during the test-retest series, with a mean percentage level of agreement of 87% (range: 72-93%).CONCLUSION: This study demonstrates that a short familiarization session enables individuals with no prior sonography experience to consistently evaluate VGE prevalence from precordial ultrasonic videos.Elia A, Ånell R, Eiken O, Grönkvist M, Gennser M. Inter- and intra-rater level of agreement in ultrasonic video grading of venous gas emboli. Aerosp Med Hum Perform. 2022; 93(1):54-57.

Human extravehicular activity (EVA) is essential to space exploration and involves risk of decompression sickness (DCS). On Earth, the effect of microgravity on physiological systems is simulated in an experimental model where subjects are confined to a 6 degrees head-down bed rest (HDBR). This model was used to investigate various resting and exercise regimen on the formation of venous gas emboli (VGE), an indicator of decompression stress, post-hyperbaric exposure. Eight healthy male subjects participating in a bed rest regimen also took part in this study, which incorporated five different hyperbaric exposure (HE) interventions made before, during and after the HDBR. Interventions i-iv were all made with the subjects lying in 6 degrees HD position. They included (C1) resting control, (C2) knee-bend exercise immediately prior to HE, (T1) HE during the fifth week of the 35-day HDBR period, (C3) supine cycling exercise during the HE. In intervention (C4), subjects remained upright and ambulatory. The HE protocol followed the Royal Navy Table 11 with 100 min spent at 18 m (280 kPa), with decompression stops at 6 m for 5 min, and at 3 m for 15 min. Post-HE, regular precordial Doppler audio measurements were made to evaluate any VGE produced post-dive. VGE were graded according to the Kisman Masurel scale. The number of bubbles produced was low in comparison to previous studies using this profile [Kisman integrated severity score (KISS) ranging from 0-1], and may be because subjects were young, and lay supine during both the HE and the 2 h measurement period post-HE for interventions i-iv. However, the HE during the end of HDBR produced significantly higher maximum bubble grades and KISS score than the supine control conditions (p < 0.01). In contrast to the protective effect of pre-dive exercise on bubble production, a prolonged period of bed rest prior to a HE appears to promote the formation of post-decompression VGE. This is in contrast to the absence of DCS observed during EVA. Whether this is due to a difference between hypo- and hyperbaric decompression stress, or that the HDBR model is a not a good model for decompression sensitivity during microgravity conditions will have to be elucidated in future studies.

During high-altitude flight, extravehicular activity, and following diving, decompression sickness (DCS) can occur. Even mild symptoms of DCS (e.g., joint pain) may jeopardise a mission and necessitate treatment to resolve. The aetiology of DCS is thought to be the generation of gas bubbles within tissues and the vascular system, the latter known as venous gas emboli (VGE). These bubbles are believed to be formed from gas-saturated tissues and precursor bubbles, also known as micronuclei. There is limited knowledge regarding potential pre-decompression events that might provoke the development of DCS. Anecdotal observations made in reports suggest a relationship between strenuous exercise and musculoskeletal injury with an increased risk of DCS. However, no controlled studies in humans have been conducted to further explore this relationship. Given that aviators and divers frequently engage in strenuous physical activity, it is of interest, not least from a practical viewpoint, to determine whether and to what degree muscle damage induced by strenuous physical exercise may increase the risk of developing DCS. Eccentric contractions, where muscles lengthen under tension, cause greater exercise-induced muscle damage (EIMD) than concentric or isometric contractions. Although many eccentric exercises have been studied for their potential to cause EIMD, the effects of eccentric arm cycling remain unexplored.

In this thesis, we examined the effect of eccentric exercise on the formation of VGE as a marker of decompression strain. The thesis is based on four separate studies with the collective aim of investigating the effects of eccentric exercise on muscle damage and the formation of high-altitude-induced VGE. 

The first study investigated eccentric arm cycling as a mode of exercise to induce muscle damage. The results show that 15 minutes of eccentric arm cycling is enough to induce EIMD, as evidenced by a reduction in isometric strength, delayed onset of muscle soreness, and elevation of markers indicative of muscle damage. 

The second study investigated the effect of eccentric upper-body exercise on the formation of VGE. The study included two conditions: (i) eccentric exercise performed 24 hours prior to decompression and (ii) no exercise (Control). The results show that performing eccentric exercise 24 hours prior to a continuous exposure to 24, 000 feet for 90 minutes led to an earlier onset and increased VGE load compared to the Control. 

The third study examined the effect of EIMD and its magnitude on high-altitude-induced VGE. The study included three conditions: (i) eccentric whole-body exercise, (ii) eccentric upper body exercise, and (iii) Control. The results show that the impact of eccentric exercise on high-altitude-induced VGE seems to vary depending on whether eccentric exercise has been performed in the upper body or lower body, rather than on the total muscle mass recruited. 

The fourth study investigated the effect of eccentric exercise on muscle damage and inflammation and explored their possible roles in hypobaric VGE formation. The study included VGE-data from studies II and III, along with blood samples collected in conjunction with Control/exercise interventions and altitude exposures. The findings suggest that eccentric EIMD and inflammation are associated with a higher decompression strain. Furthermore, VGE load seems to induce and exacerbate systemic inflammation in a dose-dependent manner. 

Purpose: Animal studies have shown that recent musculoskeletal injuries increase the risk of decompression sickness (DCS). However, to date no similar experimental study has been performed in humans. The aim was to investigate if exercise-induced muscle damage (EIMD)—as provoked by eccentric work and characterized by reduced strength and delayed-onset muscle soreness (DOMS)—leads to increased formation of venous gas emboli (VGE) during subsequent hypobaric exposure. Methods: Each subject (n = 13) was on two occasions exposed to a simulated altitude of 24,000 ft for 90 min, whilst breathing oxygen. Twenty-four hours prior to one of the altitude exposures, each subject performed 15 min of eccentric arm-crank exercise. Markers of EIMD were reduction in isometric m. biceps brachii strength and DOMS as assessed on the Borg CR10 pain scale. The presence of VGE was measured in the right cardiac ventricle using ultrasound, with measurements performed at rest and after three leg kicks and three arm flexions. The degree of VGE was evaluated using the six-graded Eftedal–Brubakk scale and the Kisman integrated severity score (KISS). Results: Eccentric exercise induced DOMS (median 6.5), reduced the biceps brachii strength (from 230 ± 62 N to 151 ± 8.8 N) and increased the mean KISS at 24,000 ft, both at rest (from 1.2 ± 2.3 to 6.9 ± 9.2, p = 0.01) and after arm flexions (from 3.8 ± 6.2 to 15.5 ± 17.3, p = 0.029). Conclusion: EIMD, induced by eccentric work, provokes release of VGE in response to acute decompression.

Purpose: There is a scarcity of information regarding the effect of upper-body eccentric exercise on biomarkers of muscle damage. This study sought to investigate the effect of eccentric arm cycling on muscle damage [exercise-induced muscle damage (EIMD)].

Method: Ten subjects performed a 15 min eccentric arm cycling protocol (cadence 49 ± 7 rpm, power absorbed 248 ± 34 W). Maximal voluntary contraction (MVC) of the elbow flexors was evaluated at rest and at 5 min, 24 h, and 48 h post-exercise. In addition, blood samples were drawn at rest and thereafter at 30 min, 24 h, and 48 h intervals after exercise for quantification of creatine kinase (CK), myoglobin, lactate dehydrogenase (LDH) and endothelin (ET-1) concentrations. Delayed onset muscle soreness (DOMS) was assessed using a category ratio scale (0-10).

Results: Myoglobin was increased from baseline at 30 min post-exercise (+114%, 46.08 ± 22.17 µg/L, p = 0.018). Individual peak values were higher than baseline values for CK (+72.8%, 204 ± 138 U/L, p = 0.046) and LDH (+17%, 3.3 ± 0.88 nmole/min/mL, p = 0.017), but not for ET-1 (+9%, 1.4 ± 0.48 pg/mL, p = 0.45). DOMS was reported at 24 h (median 4) and 48 h (median 4) post-exercise and MVC of the elbow flexors were reduced from baseline (216 ± 44 N) at 5 min (-34%, 147 ± 61 N, p < 0.001), 24 h (-17%, 181 ± 56 N, p = 0.005) and 48 h (-9%, 191 ± 54 N, p = 0.003).

Conclusion: Eccentric arm cycling incites EIMD with reduced MVC and elevation of myoglobin, CK and LDH.

Eccentric upper-body exercise performed 24 h prior to high-altitude decompression has previously been shown to aggravate venous gas emboli (VGE) load. Yet, it is unclear whether increasing the muscle mass recruited (i.e., upper vs. whole-body) during eccentric exercise would exacerbate the decompression strain. Accordingly, this study aimed to investigate whether the total muscle mass recruited during eccentric exercise influences the decompression strain. Eleven male participants were exposed to a simulated altitude of 24,000 ft for 90 min on three separate occasions. Twenty-four hours before each exposure, participants performed one of the following protocols: (i) eccentric whole-body exercise (ECCw; squats and arm-cycling exercise), (ii) eccentric upper-body exercise (ECCu; arm-cycling), or (iii) no exercise (control). Delayed onset muscle soreness (DOMS) and isometric strength were evaluated before and after each exercise intervention. VGE load was evaluated at rest and after knee- and arm-flex provocations using the 6-graded Eftedal-Brubakk scale. Knee extensor (-20 ± 14%, P = 0.001) but not elbow flexor (-12 ± 18%, P = 0.152) isometric strength was reduced 24 h after ECCw. ECCu reduced elbow flexor isometric strength at 24 h post-exercise (-18 ± 10%, P < 0.001). Elbow flexor DOMS was higher in the ECCu (median 6) compared with ECCw (5, P = 0.035). VGE scores were higher following arm-flex provocations in the ECCu (median (range), 3 (0-4)) compared with ECCw (2 (0-3), P = 0.039) and control (0 (0-2), P = 0.011), and in ECCw compared with control (P = 0.023). VGE were detected earlier in ECCu (13 ± 20 min) compared with control (60 ± 38 min, P = 0.021), while no differences were noted between ECCw (18 ± 30 min) and control or ECCu. Eccentric exercise increased the decompression strain compared with control. The VGE load varied depending on the body region but not the total muscle mass recruited.

HIGHLIGHTS: What is the central question of this study? Does exercise-induced muscle damage (EIMD) resulting from eccentric exercise influence the presence of venous gas emboli (VGE) during a 90 min continuous exposure at 24,000 ft? What is the main finding and its importance? EIMD led to an earlier manifestation and greater VGE load compared with control. However, the decompression strain was dependent on the body region but not the total muscle mass recruited.

This study aimed to investigate the effect of eccentric exercise on exercise-induced muscle damage (EIMD) and inflammation on high-altitude-induced venous gas emboli (VGE). Subjects were exposed to an altitude of 24,000 ft. for 90 min, with either prior eccentric exercise (ECC) or no exercise (Control) 24 h before. Blood samples were collected at baseline (T0), before (T1), and after (T2) altitude exposures. VGE load was evaluated using the Eftedal-Brubakk (ΕΒ) scale. Creatine kinase (CK) and myoglobin were used to assess muscle damage, while interleukin-6 (IL-6), tumor necrosis factor alpha (TNF-α), C-reactive protein (CRP), and fibrinogen were used to evaluate inflammation. ECC showed higher EB-scores during altitude exposures [median(range), 3(0–5)] than Control [1(0–4), p = 0.019]. Increases in myoglobin (+35%, p = 0.012), CK (+130%, p < 0.001), IL-6 (+72%, p = 0.02), and CRP (+63%, p = 0.004) were observed from T0 to T1 in ECC, but not Control. Significantly higher levels of myoglobin (p = 0.033), CK (p < 0.001), IL-6 (p = 0.016), and CRP (p = 0.002) were noted in the ECC compared to Control at T1. IL-6 increased from T1 to T2 in ECC (p = 0.005), with higher levels than Control at T2 (p = 0.046). A correlation was found between EB-scores and T1 myoglobin levels (rs = 0.450; p = 0.004), and to T1-T2 IL-6 changes (rs = 0.396; p = 0.037). Eccentric EIMD followed by inflammation is associated with a higher decompression strain, with VGE load aggravating systemic inflammation.

BACKGROUND: The study investigated the heat strain of personnel operating in the rear cabin of a helicopter during desert-climate missions, and to what extent the strain can be mitigated by use of battery-driven ventilation vests.

METHODS: Eight men undertook 3-h simulated flight missions in desert conditions (45 degrees C, 10% humidity, solar radiation). Each subject participated in three conditions wearing helicopter flight equipment, including body armor, and either: a ventilation vest with a 3-dimensional mesh (Vent-1), a ventilation vest with a foam sheet incorporating channels to direct the air flow (Vent-2), or a T-shirt (NoVent); each mission comprised a 10-min walk, followed by sitting for 30 min, kneeling on a vibration platform for 2 h, and finally 30 min of sitting. Core temperature, heart rate, skin temperatures and heat flux, oxygen uptake, sweating rate, and subjective ratings were recorded. Evaporative capacity and thermal resistance of the garments were determined using a thermal manikin.

RESULTS: All subjects completed the NoVent and Vent-1 conditions, whereas in the Vent-2 condition, one subject finished prematurely due to heat exhaustion. The increase in core temperature was significantly (P <= 0.01) greater in Novent (0.93 degrees C) and Vent-2 (0.88 degrees C) than in Vent-1 (0.61 degrees C). Evaporative capacity was significantly higher for Vent-1 (7.8 g . min(-1)) than for NoVent (4.1 g . min(-1)) and Vent-2 (4.4 g . min(-1)).

DISCUSSION: Helicopter personnel may be at risk of heat exhaustion during desert missions. The risk can be reduced by use of a ventilation vest. However, the cooling efficacy of ventilation vests differs substantially depending on their design and ventilation concept.

The study examined the effects of short-term field-based military training with partial sleep deprivation on whole-body endurance performance in well-trained individuals. Before and after a 2-day sustained operations (SUSOPS), 14 cadets performed a 15-min constant-load cycling at 65% of peak power output (PPO; CLT65), followed by an exhaustive constant-load trial at 85% of PPO (CLT85). Physiological [oxygen uptake (O-2), heart rate (HR), mean arterial pressure (MAP), cardiac output (CO), and regional oxygenation (TOI) in the frontal cerebral cortex and vastus lateralis muscle] and psychological [effort perception (RPE), affective valence (FS), and perceived activation (FAS)] variables were monitored during exercise. SUSOPS reduced time to exhaustion in CLT85 by 29.1% (p = 0.01). During the CLT65 trial, SUSOPS potentiated the exercise-induced elevations in O-2 and HR (p < 0.05), and blunted MAP (p = 0.001). CO did not differ between trials. Yet, towards the end of both CLT85 trials, CO tended to decline (p 0.08); a response that occurred at an earlier stage in the SUSOPS trial. During CLT65, SUSOPS altered neither cerebral nor muscle TOI. The SUSOPS CLT85 trial, however, was terminated at similar leg-muscle deoxygenation (p > 0.05) and lower prefrontal cortex deoxygenation (p < 0.01). SUSOPS increased RPE at submaximal intensities (p = 0.05), and suppressed FAS and FS throughout (p < 0.01). The present findings indicate, therefore, that a brief period of military sustained operations with partial sleep deprivation augment cardiorespiratory and psychological strain, limiting high-intensity endurance capacity.

When entering a coordinated flight turn without visual references, the perception of roll-angular displacement is determined by vestibular cues, and/or probably by assessment of the gravitoinertial (G) load (G magnitude) and its translation into the corresponding bank angle. Herein, we examined whether repeated exposures to hypergravity (G training) in a centrifuge, would advance, not only the ability to accurately assess the G load but also the capacity to detect or estimate the corresponding roll inclination of the centrifuge gondola. To this end, in nine men without piloting experience, the subjective estimation of G load and roll tilt were assessed, in complete darkness, during 5-min coordinated turns in the centrifuge, performed at 1.1 G (25 degrees roll-tilt angle) and 2.0 G (60 degrees roll tilt angle). These trials were conducted before and after 5 wk of G training {3 x 40-min sessions<middle dot>wk-1; protocol: 20 x 1 min at G levels close to the individual relaxed G-level tolerance [range: similar to 2.6 G (similar to 67 degrees)-3.6 G (74 degrees)], separated by 1-min intervals at idle speed (1.4 G)}, whereas continual feedback to the subjects was limited to the G load. As expected, G training improved subjects' capacity to assess G load, especially at 2.0 G (P = 0.006). The perception of roll tilt, however, was consistently underestimated (by similar to 70%-80%), and not enhanced by G training (P >= 0.51). The present findings demonstrate that prolonged repeated G-induced roll-tilts in a centrifuge gondola, while external feedback is restricted to graviception, enhance the capacity to perceive G load, but fail to advance the ability to detect or consciously estimate the magnitude of roll-angular displacement during a coordinated turn. NEW & NOTEWORTHY During a coordinated flight turn without external visual references, the pilot typically underestimates the aircraft bank angle, because unreliable information of roll tilt is conveyed by the vestibular system. The present results demonstrate that prolonged repeated gravitoinertial (G)-induced roll-tilts in a centrifuge gondola, while external feedback is restricted to graviception, enhance the capacity to perceive G load, but fail to advance the ability to consciously estimate the magnitude of roll angular displacement.

Purpose

We evaluated the hypothesis that repetitive gravitoinertial stress would augment the arterial-pressure response to peripheral sympathetic stimulation.

Methods

Before and after a 5-weeks G-training regimen conducted in a human-use centrifuge, twenty healthy men performed a hand cold-pressor test, and nine of them also a foot cold-pressor test (4 min; 4 °C water). Arterial pressures and total peripheral resistance were monitored.

Results

The cold-induced elevation (P ≤ 0.002) in arterial pressures and total peripheral resistance did not vary between testing periods, either in the hand [mean arterial pressure: Before =  + 16% vs. After =  + 17% and total peripheral resistance: Before =  + 13% vs. After =  + 15%], or in the foot [mean arterial pressure: Before =  + 19% vs. After =  + 21% and total peripheral resistance: Before =  + 16% vs. After =  + 16%] cold-pressor tests (P > 0.05).

Conclusion

Present results demonstrate that 5 weeks of prolonged iterative exposure to hypergravity does not alter the responsiveness of sympathetically mediated circulatory reflexes.

We sought to examine whether short-term, whole body cold acclimation would modulate finger vasoreactivity and thermosensitivity to localized cooling. Fourteen men were equally assigned to either the experimental (CA) or the control (CON) group. The CA group was immersed to the chest in 14°C water for ≥120 min daily over a 5-day period while the skin temperature of the right-hand fingers was clamped at ∼35.5°C. The CON group was instructed to avoid any cold exposure during this period. Before and after the intervention, both groups performed, on two different consecutive days, a local cold provocation trial consisting of a 30-min hand immersion in 8°C water while immersed to the chest once in 21°C (mild-hypothermic trial; 0.5°C fall in rectal temperature from individual preimmersion values) and on the other occasion in 35.5°C (normothermic trial). In the CA group, the cold-induced reduction in finger temperature was less (mild-hypothermic trial: P = 0.05; normothermic trial: P = 0.02), and the incidence of the cold-induced vasodilation episodes was greater (in normothermic trials: P = 0.04) in the post- than in the preacclimation trials. The right-hand thermal discomfort was also attenuated (mild-hypothermic trial: P = 0.04; normothermic trial: P = 0.01). The finger temperature responses of the CON group did not vary between testing periods. Our findings suggest that repetitive whole body exposure to severe cold within a week may attenuate finger vasoreactivity and thermosensitivity to localized cooling. These regional thermo-adaptions were ascribed to central neural habituation produced by the iterative, generalized cold stimulation.

We examined the interactive effects of mild hypothermia and hypoxia on finger vasoreactivity to local cold stress. Eight male lowlanders performed, in a counterbalanced order, a normoxic and a hypoxic (partial pressure of oxygen: similar to 12 kPa) hand cold provocation (consisting of a 30-min immersion in 8 degrees C water), while immersed to the chest either in 21 degrees C [cold trials; 0.5 degrees C fall in rectal temperature (T-rec) from individual preimmersion values], or in 35.5 degrees C water, or while exposed to 27 degrees C air. The duration of the trials was kept constant in each breathing condition. Physiological (T-rec, skin temperature, cutaneous vascular conductance, oxygen uptake) and perceptual (thermal sensation and comfort, local pain, affective valence) reactions were monitored continually. Hypoxia accelerated the drop in T-rec by similar to 14 min (P = 0.06, d = 0.67). In the air-exposure trials, hypoxia did not alter finger perfusion during the local cooling. whereas it impaired the finger rewarming response following the cooling (P < 0.01). During the 35.5 degrees C immersion, the finger vasomotor tone was enhanced, especially in hypoxia (P = 0.01). Mild hypothermia aggravated finger vasoconstriction instigated by local cooling (P < 0.01), but the response did not differ between the two breathing conditions (P > 0.05). Hypoxia tended to attenuate the sensation of coldness (P = 0.10, r = 0.40) and thermal discomfort (P = 0.09, r = 0.46) in the immersed hand. Both in normoxia and hypoxia, the whole body thermal state dictates the cutaneous vasomotor reactivity to localized cold stimulus.

The study examined intra- and interlimb variations in cutaneous vessel responsiveness to acute and repeated transmural pressure elevations. In 11 healthy men, red blood cell flux was assessed via laser-Doppler flowmetry on both glabrous and nonglabrous skin regions of an arm (finger and forearm) and leg (toe and lower leg), across a wide range of stepwise increasingdistending pressures imposed in the vessels of each limb separately. The pressure-flux cutaneous responses were evaluatedbefore and after 5 wk of intermittent (40 min, 3 sessions per week) exposures to hypergravity (2.6–3.3 G; G training). Beforeand after G training, forearm and lower leg blood flux were relatively stable up to 210 and 240 mmHg distending pressures,respectively; and then they increased two- to threefold (P < 0.001). Finger blood flux dropped promptly (P < 0.001), regardlessof the G training (P = 0.64). At 120-mmHg distending pressures, toe blood flux enhanced by 40% (P  0.05); the increasewas augmented after the G training (P = 0.01). At high distending pressures, toe blood flux dropped by 70% in both trials (P <0.001). The present results demonstrate that circulatory autoregulation is more pronounced in glabrous skin than in nonglabrousskin, and in nonglabrous sites of the leg than in those of the arm. Repetitive high-sustained gravitoinertial stress does not modifythe pressure-flow relationship in the dependent skin vessels of the arm nor in the nonglabrous sites of the lower leg. Yet it maypartly inhibit the myogenic responsiveness of the toe’s glabrous skin.

The purpose of the study was to evaluate the recuperative efficacy of pre-exercise napping on physical capacity after military sustained operations (SUSOPS) with partial sleep deprivation. Before and after a 2-day SUSOPS, 61 cadets completed a battery of questionnaires, and performed a 2-min lunges trial and a 3,000-m running time-trial. After the completion of SUSOPS, subjects were randomized to either a control [without pre-exercise nap (CON); n = 32] or a nap [with a 30-min pre-exercise nap (NAP); n = 29] group. SUSOPS enhanced perceived sleepiness and degraded mood in both groups. Following SUSOPS, the repetitions of lunges, in the CON group, were reduced by similar to 2.3%, albeit the difference was not statistically significant (p = 0.62). In the NAP group, however, the repetitions of lunges were increased by similar to 7.1% (p = 0.01). SUSOPS impaired the 3,000-m running performance in the CON group (similar to 2.3%; p = 0.02), but not in the NAP group (0.3%; p = 0.71). Present results indicate, therefore, that a relatively brief pre-exercise nap may mitigate physical performance impairments ensued by short-term SUSOPS.

Cold and hypoxia constitute the main environmental stressors encountered on the Antarctic Plateau. Hence, we examined whether central and/or peripheral acclimatisation to the combined stressors of cold and hypoxia would be developed in four men following an 11-day man-hauling expedition on this polar region. Before and after the journey, participants performed a static whole-body immersion in 21 degrees C water, during which they were breathing a hypoxic gas (partial pressure of inspired 02: 97 mmHg). To evaluate their local responses to cold, participants also immersed the hand into 8 degrees C water for 30 min, while they were whole-body immersed and mildly hypothermic [i.e. 0.5 degrees C fall in rectal temperature (T-rec) from individual pre-immersion values]. T-rec, and aldn temperature (T-ak), skin blood flux, and oxygen uptake (reflecting shivering thermogenesis) were monitored throughout. The polar expedition accelerated by similar to 14 min the drop in Trr, [final mean (95% confidence interval) changes in T-rec: Before = -0.94 (0.15) degrees C, After: 1.17 (0.23) degrees C]. The shivering onset threshold [Before: 19 (22) min, After: 25 (19) min] and gain [Before: 4.19 (3.95) mL min(-1) kg, After: 1.70 (1.21) mi. min(-1) kg(-1)] were suppressed by the expedition. TA did not differ between trials. The development of a greater post expedition hypothermic state did not compromise finger circulation during the hand-cooling phase. Present findings indicate therefore that a hypothermic pattern of cold acclimatisation, as investigated in hypoxia, was developed following a short-term expedition on the South Polar Plateau; an adaptive response that is characterised mainly by suppressed shivering thermogenesis, and partly by blunted cutaneous vasoconstriction.

When combining two conditions of reduced oxygen availability, anemia and hypoxia, human physiological responses are highly challenged to maintain arterial oxygen delivery, especially during whole-body exercise. The aim of this study was to compare the cardiorespiratory responses of mildly anemic women with those of healthy controls, while cycling in normobaric hypoxia. Two groups of young females were matched for age, weight, height, and involvement in physical activity, one with normal hemoglobin, hematocrit, and ferritin levels and another suffering from mild iron deficiency anemia (10 < (Hb) < 12 g/dL, 34 < Hct < 37%, ferritin < 15 μg/L). They cycled to exhaustion under normoxia and hypoxia (FIO2 0.21 and 0.14), and their physiological responses were compared at 40, 80, and 100% VO2max of the specific condition. The two groups differed (p < 0.05) mainly at the higher exercise intensities; the anemic participants exhibited similar heart rate but lower oxygen pulse than their control counterparts, as well as a larger drop in maximal oxygen uptake. However, they sustained maximal effort by employing the anaerobic metabolism to a larger extent, which stimulated a greater ventilatory response. It appears that iron deficiency anemia of mild severity, which is commonly observed in young athletic females, impacts physiological responses during whole-body exercise in the presence of moderate hypoxia.

NEW FINDINGS: What is the central question of this study? Does a 35-day horizontal bedrest impair thermoeffector responses during whole-body submaximal exercise performed in temperate conditions? What is the main finding and its importance? Cardiovascular and muscular deconditioning ensued from prolonged recumbency, seems to augment, at least to a degree, the exercise-induced increase in body core temperature, most likely due to an impairment in non-evaporative heat loss. The response is a function of the absolute exercise intensity imposed.

ABSTRACT: We examined the effects of a 35-day horizontal bedrest on thermoregulation during whole-body exercise. Fifteen healthy men were randomly assigned to either a bedrest (BR; n = 10), or a control (CON; n = 5) group. Prior to bedrest, both groups performed a 40-min constant-load upright cycling at 30% of their peak workload (W_peak ; PRE). One and two days after bedrest, the BR group performed, in a randomised counterbalanced order, two 40-min trials at 30% of: (i) the pre-bedrest W_peak (i.e., at a fixed absolute intensity; POST-A), and (ii) the post-bedrest W_peak (i.e., at a fixed relative intensity; POST-R). The CON group conducted only the POST-A trial, at the same time intervals. During the trials, rectal (T_rec ) and skin temperatures, and the forehead sweating rate (SwR) were monitored. In the CON group, no differences were observed between the trials. Bedrest potentiated moderately the T_rec elevation during the latter part of POST-A (∼0.10°C; P≤0.05), but not of POST-R (∼0.04°C; P = 0.11). In both post-bedrest trials, was attenuated by ∼1.5-2.0^° C throughout (P<0.01), whereas the forehead SwR was not modulated. T_rec and were similar in POST-A and POST-R; yet the forehead SwR was more dependent on the relative workload imposed (P = 0.04). Present findings therefore suggest that the cardiovascular and muscular deconditioning ensued from a 35-day bedrest may aggravate the exercise-induced increase in body core temperature when working at a given absolute intensity, most likely due to an impairment in non-evaporative heat loss. This article is protected by copyright. All rights reserved.

Background: Echocardiography is usually performed with the subject/patient lying in the left lateral position (LLP), because the acoustic window is better in this than in the supine position (SP). The aim was to investigate cardiac responses to rotational changes of position in the transversal plane, from SP to LLP while horizontal, and from leaning on the back (HUT-LB) to leaning on the left side (HUT-LL) while tilted 60° head-up from the horizontal. Methods: Healthy men (n = 12) underwent 10-min HUT provocations. Cardiac variables were measured using two-dimensional echocardiography, Doppler, tissue Doppler imaging and arterial pressures using a volume-clamp method. Results: In horizontal posture, cardiac volumes were smaller in SP than in LLP: end-diastolic volume (EDV) by 14%, end-systolic volume (ESV) by 13%, stroke volume (SV) by 14%, and cardiac output (CO) by 16% (P<0·03). In addition, the mitral annular plane systolic excursion (MAPSE) was 11% smaller (P = 0·001) and the left ventricle isovolumic relaxation time (IVRT) 27% longer in SP than in LLP. The ejection fraction, heart rate, arterial pressure and pulmonary ventilation were similar in SP and LLP. During HUT, EDV, SV, CO and MAPSE were smaller, and IVRT was longer, in HUT-LB than in HUT-LL, by −19%, −20%, −17%, −18% and +35%, respectively (P<0·04). Conclusions: Cardiac performance is enhanced in LLP versus SP and in HUT-LL versus HUT-LB, which can be attributed to improved venous return, conceivably, wholly or in part, due to increased hydrostatic pressure gradients between the caval veins and the heart in the LLP and HUT-LL positions.

Background: Underwater rugby is a team sport where players try to score points with a negatively buoyant ball while submerged in a swimming pool. Reports of syncope incidents at the Swedish Championships led to us to investigate end-tidal oxygen and carbon dioxide levels during simulated match play. Methods: Eight male underwater rugby club players of varying experience participated. Repetitive measurements were made while players were defending during simulated match play. Each time a player surfaced they exhaled through a mouthpiece connected to a flow meter and a gas analyzer to measure tidal volume, PETO2 and PETCO2. Results: Measurements were made over 12 dives, with an average dive duration of 18.5 seconds. The mean maximal PETCO2 across the eight participants was 10.0 kPa (similar to 75 mmHg) (range, 9.1-11.7 [-68-88]). The corresponding mean minimum PETO2 was 7.6 kPa (similar to 57 mmHg) (6.3-10.4 [similar to 47-78)). PETCO2 drifted upward, with the mean upward change from the first to last dive for each participant being +1.8 (similar to 13.5 mmHg) (SD 1.74) kPa. A similar trend for PETO2 was not detected, with a mean change of similar to 0.1 (similar to 0.75 mmHg) (SD 3.79) kPa. Conclusion: Despite high PETCO2 values that were close to narcotic being recorded, these players seemed to regulate their urge to breathe based on hypoxia rather than hypercapnia.

This study assessed the influence of a 10-day hypoxic bed rest on cartilage biomarkers and subchondral bone density across the patellofemoral joint (PFJ). Within clinical settings hypoxic tissue may arise in several types of disorders. Furthermore, a hypoxic environment is being considered for space flight habitats in the near future. Female participants (N = 12) participated in this study comprising three 10-day interventions: hypoxic ambulation (HAMB), normoxic bed rest (NBR), and hypoxic bed rest (HBR). Venous samples were collected prior to (day -2: Pre) and during the intervention (days 2 and 5), immediately before reambulation (D11) and 24 hr post intervention (R1). Blood samples were analyzed for: aggrecan, hyaluronan, Type IIA procollagen amino terminal propeptide (PIIANP), and cartilage oligomeric matrix protein (COMP). Total bone mineral density (BMD) in eight regions (2 mm × 10 mm) across the PFJ was determined. The three interventions (HAMB, HBR, and NBR) did not induce any significant changes in the cartilage biomarkers of hyaluronan or PIIANP. Aggrecan increased during the HAMB trial to 2.02 fold the Pre value. COMP decreased significantly in both NBR & HBR compared to HAMB on D5. There were significant differences in BMD measured across the PFJ from cortical patellar bone (735 to 800 mg/cm³ ) to femur trabecular (195 to 226 mg/cm³ ). However, there were no significant changes in BMD from Pre to Post bed rest. These results indicate that there were no significant detectable effects of inactivity/unloading on subchondral bone density. The biomarker of cartilage, COMP, decreased on D5, whereas the addition of hypoxia to bed rest had no effect, it appears that hypoxia in combination with ambulation counteracted this decrease.

Due to the observations of weight loss at high altitude, normobaric hypoxia has been considered as a method of weight loss in obese individuals. With this regard, the aim of the present study was to determine the effect of hypoxia per se on metabolism in men with excess weight. Eight men living with excess weight (125.0 ± 17.7 kg; 30.5 ± 11.1 years, BMI: 37.6 ± 6.2 kg⋅m^-2) participated in a randomized cross-over study comprising two 10-day confinements: normobaric (altitude of facility ≃ 940 m) normoxia (NORMOXIA; P _I O₂ = 133 mmHg), and normobaric hypoxia (HYPOXIA). The P _I O₂ in the latter was reduced from 105 (simulated altitude of 2,800 m) to 98 mmHg (simulated altitude of 3,400 m over 10 days. Before, and at the end of each confinement, participants completed a meal tolerance test (MTT). Resting energy expenditure (REE), circulating glucose, GLP-1, insulin, catecholamines, ghrelin, peptide-YY (PYY), leptin, gastro-intestinal blood flow, and appetite sensations were measured in fasted and postprandial states. Fasting REE increased after HYPOXIA (+358.0 ± 49.3 kcal⋅day^-1, p = 0.03), but not after NORMOXIA (-33.1 ± 17.6 kcal⋅day^-1). Postprandial REE was also significantly increased after HYPOXIA (p ≤ 0.05), as was the level of PYY. Furthermore, a tendency for decreased energy intake was concomitant with a significant body weight reduction after HYPOXIA (-0.7 ± 0.2 kg) compared to NORMOXIA (+1.0 ± 0.2 kg). The HYPOXIA trial increased the metabolic requirements, with a tendency toward decreased energy intake concomitant with increased PYY levels supporting the notion of a hypoxia-induced appetite inhibition, that could potentially lead to body weight reduction. The greater postprandial blood-glucose response following hypoxic confinement, suggests the potential development of insulin resistance.

BACKGROUND: Fatigue of air force pilots has become an increasing concern due to changes in mission characteristics. In the current study we investigated fatigue, emotions, and cognitive performance in a simulated 11-h mission in the 39 Gripen fighter aircraft. METHODS: A total of 12 subjects were evaluated in a high-fidelity dynamic flight simulator for 12 consecutive hours. Perceived fatigue was measured by the Samn-Perelli Fatigue Index (SPFI). Emotions were assessed with the Circumplex Affect Space. Cognitive performance was assessed by five cognitive tasks. RESULTS: Significant increase in self-reported fatigue, general decrease in two positive emotional states, as well increase of one negative emotional state occurred after approximately 7 h into the mission. Self-reported fatigue negatively correlated with enthusiasm and cheerfulness (r' = -0.75; -0.49, respectively) and positively correlated with boredom and gloominess (r' = -0.61; r' = -0.30, respectively). Response time in the low-order task negatively correlated with enthusiasm, cheerfulness and calmness (r' = -0.44; r' = -0.41; r' = -0.37, respectively) and positively correlated with boredom and anxiousness (r' = 0.37; r' = 0.28, respectively). Mission duration had an adverse impact on emotions in these environmental conditions, particularly after 7 h. DISCUSSION: These results contribute to the understanding of fatigue development in general and of emotion-cognition relationships. These findings emphasize that both emotional states and the type of cognitive tasks to be performed should be considered for planning long-duration missions in single-piloted fighter aircrafts as to increase the probability of missions' success.

Purpose: It is speculated that diving might be harmful to the nervous system. The aim of this study was to determine if established markers of neuronal injury were increased in the blood after diving. Methods: Thirty-two divers performed two identical dives, 48 h apart, in a water-filled hyperbaric chamber pressurized to an equivalent of 42 m of sea water for 10 min. After one of the two dives, normobaric oxygen was breathed for 30 min, with air breathed after the other. Blood samples were obtained before and at 30–45 and 120 min after diving. Concentrations of glial fibrillary acidic, neurofilament light, and tau proteins were measured using single molecule array technology. Doppler ultrasound was used to detect venous gas emboli. Results: Tau was significantly increased at 30–45 min after the second dive (p < 0.0098) and at 120 min after both dives (p < 0.0008/p < 0.0041). Comparison of matching samples showed that oxygen breathing after diving did not influence tau results. There was no correlation between tau concentrations and the presence of venous gas emboli. Glial fibrillary acidic protein was decreased 30–45 min after the first dive but at no other point. Neurofilament light concentrations did not change. Conclusions: Tau seems to be a promising marker of dive-related neuronal stress, which is independent of the presence of venous gas emboli. Future studies could validate these results and determine if there is a quantitative relationship between dive exposure and change in tau blood concentration.

This retrospective study was designed to analyze the interindividual variability in the responses of different variables characterizing the skeletal muscle oxidative function to normoxic (N-BR) and hypoxic (H-BR) bed rests and to a hypoxic ambulatory confinement (H-AMB) of 10 and 21 days. We also assessed whether and how the addition of hypoxia to bed rest might influence the heterogeneity of the responses. In vivo measurements of O-2 uptake and muscle fractional O-2 extraction were carried out during an incremental one-leg knee-extension exercise. Mitochondrial respiration was assessed in permeabilized muscle fibers. A total of 17 subjects were included in this analysis. This analysis revealed a similar variability among subjects in the alterations induced by N-BR and H-BR both in peak O2 uptake (SD: 4.1% and 3.3% after 10 days; 4.5% and 8.1% after 21 days, respectively) and peak muscle fractional O2 extraction (SD: 5.9% and 7.3% after 10 days; 6.5% and 7.3% after 21 days), independently from the duration of the exposure. The individual changes measured in these variables were significantly related (r = 0.66, P = 0.004 after N-BR; r = 0.61, P = 0.009 after H-BR). Mitochondrial respiration showed a large variability of response after both N-BR (SD: 25.0% and 15.7% after 10 and 21 days) and H-BR (SD: 13.0% and 19.8% after 10 and 21 days); no correlation was found between N-BR and H-BR changes. When added to bed rest, hypoxia altered the individual adaptations within the mitochondria but not those intrinsic to the muscle oxidative function in vivo, both after the short- and medium-term exposures.

Skeletal muscle oxidative function was evaluated in 11 healthy males (mean +/- SD age 27 +/- 5years) prior to (baseline data collection, BDC) and following a 21day horizontal bed rest (BR), carried out in normoxia (P-IO2=133 mmHg; N-BR) and hypoxia (P-IO2=90 mmHg; H-BR). H-BR was aimed at simulating reduced gravity habitats. The effects of a 21day hypoxic ambulatory confinement (P-IO2=90 mmHg; H-AMB) were also assessed. Pulmonary O-2 uptake (<(V) over dot>O-2), vastus lateralis fractional O-2 extraction (changes in deoxygenated haemoglobin+myoglobin concentration, Delta[deoxy(Hb+Mb)]; near-infrared spectroscopy) and femoral artery blood flow (ultrasound Doppler) were evaluated during incremental one-leg knee-extension exercise (reduced constraints to cardiovascular O-2 delivery) carried out to voluntary exhaustion in a normoxic environment. Mitochondrial respiration was evaluated ex vivo by high-resolution respirometry in permeabilized vastus lateralis fibres. <(V) over dot>(O2peak) decreased (P<0.05) after N-BR (0.98 +/- 0.13 L min(-1)) and H-BR (0.96 +/- 0.17 L min(-1)) vs. BDC (1.05 +/- 0.14 L min(-1)). In the presence of a decreased (by similar to 6-8%) thigh muscle volume, <(V) over dot>(O2peak) normalized per unit of muscle mass was not affected by both interventions. Delta[deoxy(Hb+Mb)](peak) decreased (P<0.05) after N-BR (65 +/- 13% of limb ischaemia) and H-BR (62 +/- 12%) vs. BDC (73 +/- 13%). H-AMB did not alter <(V) over dot>(O2peak) or Delta[deoxy(Hb+Mb)](peak). An overshoot of Delta[deoxy(Hb+Mb)] was evident during the first minute of unloaded exercise after N-BR and H-BR. Arterial blood flow to the lower limb during both unloaded and peak knee extension was not affected by any intervention. Maximal ADP-stimulated mitochondrial respiration decreased (P<0.05) after all interventions vs. control. In 21day N-BR, a significant impairment of oxidative metabolism occurred downstream of cardiovascular O-2 delivery, affecting both mitochondrial respiration and presumably the intramuscular matching between O-2 supply and utilization. Superposition of H on BR did not worsen the impairment induced by BR alone.

The aim was to compare the musculoskeletal load distribution and muscle activity in two types of maximal flywheel leg-extension resistance exercises: horizontal leg press, during which the entire load is external, and squat, during which part of the load comprises the body weight. Nine healthy adult habitually strength-training individuals were investigated. Motion analysis and inverse dynamics-based musculoskeletal modelling were used to compute joint loads, muscle forces, and muscle activities. Total exercise load (resultant ground reaction force; rGRF) and the knee-extension net joint moment (NJM) were slightly and considerably greater, respectively, in squat than in leg press (p <= 0.04), whereas the hip-extension NJM was moderately greater in leg press than in squat (p = 0.03). Leg press was performed at 11 degrees deeper knee-flexion angle than squat (p = 0.01). Quadriceps muscle activity was similar in squat and leg press. Both exercise modalities showed slightly to moderately greater force in the vastii muscles during the eccentric than concentric phase of a repetition (p <= 0.05), indicating eccentric overload. That the quadriceps muscle activity was similar in squat and leg press, while rGRF and NJM about the knee were greater in squat than leg press, may, together with the finding of a propensity to perform leg press at deeper knee angle than squat, suggest that leg press is the preferable leg-extension resistance exercise, both from a training efficacy and injury risk perspective.

It is anticipated that flywheel-based leg resistance exercise will be implemented in future long-duration space missions, to counter deconditioning of weight-bearing bones and postural muscles. The aim was to examine low back loads and muscle engagements during flywheel leg press (FWLP) and flywheel squat (FWS) and, for comparisons, free-weight barbell back squat (BBS). Eight resistance-trained subjects performed 8 repetition maximums of FWLP, FWS, and BBS. Motion analysis and inverse dynamics-based musculoskeletal modeling were used to compute joint loads and muscle forces. Muscle activities were measured with electromyography (EMG). At the L4–L5 level, peak vertebral compression force was similarly high in all exercise modes, whereas peak vertebral posteroanterior shear force was greater (p < 0.05) in FWLP and BBS than in FWS. Among the back-extensor muscles, the erector spinae longissimus exerted the greatest peak force, with no difference between exercises. Peak force in the lumbar multifidus was lower (p < 0.05) during FWLP than during FWS and BBS. Peak EMG activity in the lumbar extensor muscles ranged between 31 and 122% of maximal voluntary isometric contraction across muscles and exercise modes, with the greatest levels in the lumbar multifidus. The vertebral compression forces and muscle activations during the flywheel exercises were sufficiently high to presume that when implementing such exercise in space countermeasure regimens, they may be capable of preventing muscle atrophy and vertebral demineralization in the lumbar region.

What is the central question of this study? Controlled-hyperthermia heat acclimation protocols induce an array of thermoregulatory and cardiovascular adaptations that facilitate exercise in hot conditions. We investigated whether this ergogenic potential can be transferred to thermoneutral normoxic or hypoxic exercising conditions. What is the main finding and its importance? We show that heat acclimation did not affect maximal cardiac output or maximal aerobic power in thermoneutral normoxic/hypoxic conditions. Heat acclimation augmented the sweating response in thermoneutral normoxic conditions. The cross-adaptation theory according to which heat acclimation could facilitate hypoxic exercise capacity is not supported by our data. ABSTRACT: Heat acclimation (HA) mitigates heat-induced decrements in maximal aerobic power (V̇O_2peak ) and augments exercise thermoregulatory responses in the heat. Whether this beneficial effect of HA is observed in hypoxic or thermoneutral conditions remains unresolved. We explored the effects of HA on exercise cardiorespiratory and thermoregulatory responses in normoxic, hypoxic, and hot conditions. Twelve males (V̇O_2peak 54.7(5.7) mL·kg^-1 ·min^-1 ) participated in a HA protocol comprising 10 daily 90-min controlled-hyperthermia (target rectal temperature, T_re  = 38.5 °C) exercise sessions. Before and after HA, we determined V̇O_2peak in thermoneutral normoxic (NOR), thermoneutral hypoxic (13.5% F_i O₂ ; HYP) and hot (35 °C, 50% RH; HE) conditions in a randomized and counterbalanced order. Preceding each maximal cycling test, a 30-min steady-state exercise at 40% of the NOR peak power output (W_peak ) was employed to evaluate thermoregulatory responses. HA induced the expected adaptations in HE: reduced T_re and submaximal heart rate (HR), enhanced sweating response and expanded plasma volume. However, HA did not affect V̇O_2peak or maximal cardiac output (CO_max ) (P = 0.61). W_peak was increased post-HA in NOR (P < 0.001) and HE (P < 0.001) by 41 ± 21 and 26 ± 22 W, respectively but not in HYP (P = 0.14). Gross mechanical efficiency was higher (P = 0.004) whereas resting T_re and sweating thresholds were lower (P < 0.01) post-HA across environments. Nevertheless, the gain of the sweating response decreased (P = 0.05) in HYP. In conclusion, our data do not support a beneficial cross-over effect of HA on V̇O_2peak in normoxic or hypoxic conditions. This article is protected by copyright.

Hypoxia and confinement have both been shown to influence emotional state. It is envisaged that the inhabitants of future planetary habitats will be exposed to concomitant confinement, reduced gravity and hypoxia. We examined the independent and combined effects of a 21-day inactivity/unloading and normobaric hypoxia under confined conditions on various psychological factors. Eleven healthy men participated in three 21-day experimental campaigns designed in a cross-over manner (1) Normobaric hypoxic ambulatory confinement, (2) Normobaric hypoxic bed rest and (3) Normobaric normoxic bed rest. The Profile of Mood States, and the Positive and Negative Affect Schedule were employed to assess the participants' psychological responses before (Pre), during (Day 7, Day 14, and Day 21) and after (Post) the confinements. The most negative psychological profile appeared on days 14 and 21 of the hypoxic bed rest campaign. A significant increase in depression, tension, and confusion was noted on days 14 and 21 of the hypoxic bed rest condition. Concomitantly, a decrease, albeit not statistically significant, in positive psychological responses was observed. The psychological profile returned to the initial level at Post following all confinements. These data suggest that the combined effect of hypoxia and bed rest induced the most negative effects on an individual's mood. However, significant intra- and inter-individual differences in psychological responses were noted and should be taken into consideration.

Adenosine plays a role in the energy supply of cells and provokes differential, hormone-like functions in circulating cells and various tissues. Its release is importantly regulated by oxygen tension. This renders adenosine and its kinetics interesting to investigate in humans subjected to low oxygen conditions. Especially for space exploration scenarios, hypoxic conditions - together with reduced gravity - represent two foreseen living conditions when planning manned long-duration space missions or planetary habitats. The PlanHab study investigated microgravity through inactivity in bed rest and normobaric hypoxia to examine their independent or combined effect on adenosine and its kinetics. Healthy male subjects (n = 14) completed three 21-day interventions: hypoxic bed rest (HBR); hypoxic ambulatory confinement (HAMB); normoxic bed rest (NBR). The interventions were separated by 4 months. Our hypothesis of a hypoxia-triggered increase in adenosine was confirmed in HAMB but unexpectedly also in NBR. However, the highest adenosine levels were noted following HBR. Furthermore, the percentage of hemolysis was elevated in HBR whereas endothelial integrity markers stayed low in all three interventions. In summary, these data suggest that neocytolysis accounts for these effects while we could reduce evidence for microcirculatory changes.

BACKGROUND: During a simulated coordinated turn in a gondola centrifuge, experienced pilots show a substantial inter-individual variability in visual measures of perceived roll tilt. Because of the centrifuge's small radius, the pattern of stimuli to the semicircular canals during acceleration of the centrifuge differs in certain respects from that of an aircraft entering a turn.

OBJECTIVE: To explore whether these differences may be of significance for the pilot's roll- plane orientation and whether individual characteristics revealed in the centrifuge correspond to those during real flight.

METHOD: 8 fixed-wing air-force pilots were tested in a centrifuge and a high-performance aircraft. The centrifuge was accelerated to 2 G (gondola inclination 60°) within 10 s. The duration at 2 G was 6 minutes. Similar profiles were created in the aircraft. The subjective visual horizontal (SVH) was measured using an adjustable luminous line in darkness. Each pilot was tested on three occasions: centrifuge (2 runs), aircraft (2 turns), centrifuge (2 runs). For each 2-G exposure, initial and final SVH values were established via curve fitting.

RESULT: Despite a large inter-individual variability (±SD), group means were similar in the aircraft (initial: 43.0±20.6°; final: 22.5±14.8°) and centrifuge (initial: 40.6±17.0°; final: 20.5±16.0°). Further, individual peculiarities in response patterns were similar in the two conditions. For both the initial and final SVH tilt there was a high correlation between centrifuge and aircraft.

CONCLUSION: The correspondence between conditions suggests that the centrifuge is an adequate means for demonstrating the fundamental motion pattern of coordinated flight and also for establishing the individual pilot's ability to perceive an aircraft's roll attitude.Findings are discussed in connection with vestibular learning and the possibility of underlying differences between pilots in the keenness for semicircular canal and somatosensory cues.