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  • 1. Aberg, A. C.
    et al.
    Thorstensson, A.
    Tarassova, O.
    Halvorsen, Kjartan
    KTH, Skolan för teknik och hälsa (STH).
    Calculations of mechanisms for balance control during narrow and single-leg standing in fit older adults: A reliability study2011Ingår i: Gait & Posture, ISSN 0966-6362, E-ISSN 1879-2219, Vol. 34, nr 3, s. 352-357Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    For older people balance control in standing is critical for performance of activities of daily living without falling. The aims were to investigate reliability of quantification of the usage of the two balance mechanisms M(1) 'moving the centre of pressure' and M(2) 'Segment acceleration' and also to compare calculation methods based on a combination of kinetic (K) and kinematic (Km) data, (K-Km), or Km data only concerning M(2). For this purpose nine physically fit persons aged 70-78 years were tested in narrow and single-leg standing. Data were collected by a 7-camera motion capture system and two force plates. Repeated measure ANOVA and Tukey's post hoc tests were used to detect differences between the standing tasks. Reliability was estimated by ICCs, standard error of measurement including its 95% Cl, and minimal detectable change, whereas Pearson's correlation coefficient was used to investigate agreement between the two calculation methods. The results indicated that for the tasks investigated, M(1) and M(2) can be measured with acceptable inter- and intrasession reliability, and that both Km and K-Km based calculations may be useful for M(2), although Km data may give slightly lower values. The proportional M(1) :M(2) usage was approximately 9:1, in both anterio-posterior (AP) and medio-lateral (ML) directions for narrow standing, and about 2:1 in the AP and of 1:2 in the ML direction in single-leg standing, respectively. In conclusion, the tested measurements and calculations appear to constitute a reliable way of quantifying one important aspect of balance capacity in fit older people.

  • 2.
    Burenius, Magnus
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), Datorseende och robotik, CVAP.
    Sullivan, Josephine
    KTH, Skolan för datavetenskap och kommunikation (CSC), Datorseende och robotik, CVAP.
    Carlsson, Stefan
    KTH, Skolan för datavetenskap och kommunikation (CSC), Datorseende och robotik, CVAP.
    Halvorsen, Kjartan
    KTH, Skolan för datavetenskap och kommunikation (CSC), Datorseende och robotik, CVAP.
    Human 3D Motion Computation from a varying Number of Cameras2011Ingår i: Image Analysis, Springer Berlin / Heidelberg , 2011, s. 24-35Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper focuses on how the accuracy of marker-less human motion capture is affected by the number of camera views used. Specifically, we compare the 3D reconstructions calculated from single and multiple cameras. We perform our experiments on data consisting of video from multiple cameras synchronized with ground truth 3D motion, obtained from a motion capture session with a professional footballer. The error is compared for the 3D reconstructions, of diverse motions, estimated using the manually located image joint positions from one, two or three cameras. We also present a new bundle adjustment procedure using regression splines to impose weak prior assumptions about human motion, temporal smoothness and joint angle limits, on the 3D reconstruction. The results show that even under close to ideal circumstances the monocular 3D reconstructions contain visual artifacts not present in the multiple view case, indicating accurate and efficient marker-less human motion capture requires multiple cameras.

  • 3. Crommert, M. E.
    et al.
    Halvorsen, Kjartan
    KTH, Skolan för teknik och hälsa (STH).
    Ekblom, M. M.
    Trunk muscle activation at the initiation and braking of bilateral shoulder flexion movements of different amplitudes2015Ingår i: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 10, nr 11, artikel-id e0141777Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The aim of this study was to investigate if trunk muscle activation patterns during rapid bilateral shoulder flexions are affected by movement amplitude. Eleven healthy males performed shoulder flexion movements starting from a position with arms along sides (0°) to either 45°, 90° or 180°. EMG was measured bilaterally from transversus abdominis (TrA), obliquus internus (OI) with intra-muscular electrodes, and from rectus abdominis (RA), erector spinae (ES) and deltoideus with surface electrodes. 3D kinematics was recorded and inverse dynamics was used to calculate the reactive linear forces and torque about the shoulders and the linear and angular impulses. The sequencing of trunk muscle onsets at the initiation of arm movements was the same across movement amplitudes with ES as the first muscle activated, followed by TrA, RA and OI. All arm movements induced a flexion angular impulse about the shoulders during acceleration that was reversed during deceleration. Increased movement amplitude led to shortened onset latencies of the abdominal muscles and increased level of activation in TrA and ES. The activation magnitude of TrA was similar in acceleration and deceleration where the other muscles were specific to acceleration or deceleration. The findings show that arm movements need to be standardized when used as a method to evaluate trunk muscle activation patterns and that inclusion of the deceleration of the arms in the analysis allow the study of the relationship between trunk muscle activation and direction of perturbing torque during one and the same arm movement © 2015 Eriksson Crommert et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

  • 4.
    Eriksson, Martin
    et al.
    KTH, Skolan för teknik och hälsa (STH), Medicinsk teknik.
    Halvorsen, Kjartan A.
    KTH, Skolan för teknik och hälsa (STH), Medicinsk teknik.
    Gullstrand, Lennart
    Immediate effect of visual and auditory feedback to control the running mechanics of well-trained athletes2011Ingår i: Journal of Sports Sciences, ISSN 0264-0414, E-ISSN 1466-447X, Vol. 29, nr 3, s. 253-262Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The correlation between mechanical factors of running and running economy as measured by metabolic cost is a subject of much interest in the study of locomotion. However, no change in running technique has been shown to result in an immediate improvement in running economy on an intra-individual basis. To evaluate the effect of a modified running technique, it is probably necessary that the individual trains with the new technique for a longer period using a feedback system to control the new kinematics. In this study, we examine the feasibility of using visual and auditory feedback to adapt running technique according to a simplistic model of the mechanical cost of running. The model considers only the mechanical work against gravity, which is the product of the magnitude of the vertical displacement of the runner's centre of mass and the step-frequency. In the experiments reported here, 18 trained runners, running at 16km center dot h-1 on a treadmill, were given feedback on these parameters together with indicated target levels. In almost all cases, the runners were able to adjust their technique accordingly.

  • 5.
    Eriksson, Martin
    et al.
    KTH, Skolan för teknik och hälsa (STH), Medicinska sensorer, signaler och system (MSSS).
    Sturm, Dennis
    KTH, Skolan för teknik och hälsa (STH), Medicinska sensorer, signaler och system (MSSS).
    Halvorsen, Kjartan
    KTH, Skolan för teknik och hälsa (STH), Medicinska sensorer, signaler och system (MSSS).
    Gullstrand, Lennart
    Swedish Sports Confederation.
    Wireless Vertical Displacement Measurement during Running using an Accelerometer and a Mobile Phone2011Konferensbidrag (Refereegranskat)
    Abstract [en]

    The purpose of this study was to investigate in the usability of a wireless accelerometer linked to a mobile phone via Bluetooth radio for measuring vertical displacement in running athletes. Five experienced runners were monitored during lactate threshold testing at three to five different velocities. Accelerometer data was received, processed and stored on the phone to be compared to simultaneous position transducer (ground truth) recordings after data collection. A paired t-test and statistical analysis show no significant differences in the reliability of the recordings. While further investigations are encouraged, the accelerometer and algorithm (running in J2ME on the mobile phone) proof as aflexible, easy-to-use tool for out-of-the-lab monitoring and to provide real-time feedback for running technique experiments.

  • 6.
    Frohm, Anna
    et al.
    Karolinska Institute.
    Halvorsen, Kjartan
    Swedish School of Sports and Helath Sciences.
    Thorstensson, Alf
    Swedish School of Sports and Health Sciences.
    A new device for controlled eccentric overloading in training and rehabilitation2005Ingår i: European Journal of Applied Physiology, ISSN 1439-6319, E-ISSN 1439-6327, Vol. 94, nr 1-2, s. 168-174Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The aim of this work was to evaluate a device that allows for eccentric overload to be applied under controlled and safe conditions and it is applicable in exercises commonly used in training and rehabilitation. The machine contains a barbell, which is lowered and raised by a motor, following a predetermined velocity profile. It is capable of handling heavy loads (> 500 kg) and is instrumented with a sensor to measure the velocity of the barbell and two scales to measure the vertical component of the ground reaction force. The velocity recordings of the built-in displacement sensor were found to correspond well with those obtained using a motion-capture system. Applying known weights on each scale demonstrated linearity with respect to magnitude and independence regarding location of application. The velocity of the barbell was found to be dependent on the load on the barbell and on the resisting force produced by the individual training in the machine. The combined man-machine reliability was tested using a group of habitually active males (n = 13, 2855 years) performing squats. Peak voluntary resisting force and position at peak resistance were recorded on two occasions, showing no significant differences and a coefficient of variation of 9% and 22%, respectively. Preliminary observations from training in the machine have been positive both for increasing performance in top athletes and for causing pain relief in patients with diffuse knee problems. The possibility of feedback of the force under each foot makes individual dosage of training load possible, which is valuable, e.g. in rehabilitation of a unilateral injury.

  • 7.
    Frohm, Anna
    et al.
    Karolinska Institute.
    Halvorsen, Kjartan
    Swedish School of Sports and Health Sciences.
    Thorstensson, Alf
    Swedish School of Sports and Health Sciences.
    Patellar tendon load in different types of eccentric squats2007Ingår i: Clinical Biomechanics, ISSN 0268-0033, E-ISSN 1879-1271, Vol. 22, nr 6, s. 704-711Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Background. Differences in mechanical loading of the patellar tendon have been suggested as a reason for varying effects in rehabilitation of patellar tendinopathy using different eccentric squat exercises and devices. The aim was to characterize the magnitude and pattern of mechanical load at the knee and on the patellar tendon during four types of eccentric squat. Methods. Subjects performed squats with a submaximal free weight and with maximal effort in a device for eccentric overloading (Bromsman), on a decline board and horizontal surface. Kinematics was recorded with a motion-capture system, reaction forces with force plates, and electromyography from three leg muscles with surface electrodes. Inverse dynamics was used to calculate knee joint kinetics. Findings. Eccentric work, mean and peak patellar tendon force, and angle at peak force were greater (25-30%) for squats on decline board compared to horizontal surface with free weight, but not in Bromsman. Higher knee load forces (60-80%), but not work, were observed with Bromsman than free weight. Angular excursions at the knee and ankle were larger with decline board, particularly with free weight, and smaller in Bromsman than with free weight. Mean electromyography was greater on a decline board for gastrocnemius (13%) and vastus medialis (6%) with free weight, but in Bromsman only for gastrocnemius (7%). Interpretation. The results demonstrated clear differences in the biomechanical loading on the knee during different squat exercises. Quantification of such differences provides information that could be used to explain differences in rehabilitation effects as well as in designing more optimal rehabilitation exercises for patellar tendinopathy.

  • 8.
    Frohm, Anna
    et al.
    Karolinska Institute.
    Saartok, Tönuu
    Karolinska Institute.
    Halvorsen, Kjartan
    Swedish School of Sports and Health Sciences.
    Renström, Per
    Karolinska Institute.
    Eccentric treatment for patellar tendinopathy: a prospective randomised short-term pilot study of two rehabilitation protocols2007Ingår i: British Journal of Sports Medicine, ISSN 0306-3674, E-ISSN 1473-0480, Vol. 41, nr 7, s. e7-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Objective: To compare the efficacy and safety of two eccentric rehabilitation protocols for patients with symptomatic patellar tendinopathy. A new eccentric overload training device was compared with the present standard eccentric rehabilitation programme on a decline board.Design: Prospective, randomised clinical trial.Setting: Sports rehabilitation clinic, university sports laboratory, supplemented with home exercises.Patients: 20 competitive and recreational athletes, all with clinical diagnosis of patellar tendinopathy, verified by MRI or ultrasound imaging.Interventions: A 12-week rehabilitation period, either with bilateral eccentric overload strength training using the Bromsman device twice a week or with unilateral eccentric body load training using a decline board twice a week, supplemented with daily home exercises.Outcome measures: The primary outcome was pain and function, assessed by the Swedish Victorian Institute of Sport Assessment for Patella (VISA-P) score. Secondary outcome measures were isokinetic muscle torque, dynamic function and muscle flexibility, as well as pain level estimations using visual analogue scale ( VAS). Side effects were registered.Results: Both treatment groups improved in the short term according to the VISA-P scores during the 12-week rehabilitation period. However, there were no significant differences between the groups in terms of pain and function. After a 3-month rehabilitation period, most patients could be regarded as improved enough to be able to return to training and sports. No serious side effects were detected in either group.Conclusion: In patients with patellar tendinopathy pain, two-legged eccentric overload training twice per week, using the new device ( Bromsman), was as efficient and safe as the present standard daily eccentric one-legged rehabilitation-training regimen using a decline board.

  • 9. Frykberg, Gunilla E.
    et al.
    Aberg, Anna Cristina
    Halvorsen, Kjartan
    KTH, Skolan för teknik och hälsa (STH), Medicinsk teknik.
    Borg, Jorgen
    Hirschfeld, Helga
    Temporal Coordination of the Sit-to-Walk Task in Subjects With Stroke and in Controls2009Ingår i: Archives of Physical Medicine and Rehabilitation, ISSN 0003-9993, E-ISSN 1532-821X, Vol. 90, nr 6, s. 1009-1017Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Objectives: To explore events and describe phases for temporal coordination of the sit-to-walk (STW) task, within a semi standardized set up, in subjects with stroke and matched controls. In addition, to assess variability of STW phase duration and to compare the relative duration of STW phases between the 2 groups. Design: Cross-sectional. Setting: Research laboratory. Participants: A convenience sample of persons with hemiparesis (n=10; age 50-67y) more than 6 months after stroke and 10 controls matched for sex, age, height, and body mass index. Interventions: Not applicable. Main Outcome Measures: Relative duration of STW phases, SE of measurement in percentage of the mean, and intraclass correlation coefficients (ICCs). Results: Four STW phases were defined: rise preparation, transition, primary gait initiation, and secondary gait initiation. The Subjects with stroke needed 54% more time to complete the STW task than the controls did. ICCs ranged from .38 to .66 and .22 to .57 in the stroke and control groups, respectively. SEs of measurement in percentage of the mean values were high, particularly in the transition phase: 54.1% (stroke) and 50.4% (controls). The generalized linear model demonstrated that the relative duration of the transition phase was significantly longer in the stroke group. Conclusions: The present results extend existing knowledge by presenting 4 new phases of temporal coordination of STW, within a semistandardized set-up, in persons with stroke and in controls. The high degree of variability regarding relative STW phase duration was probably a result of both the semistandardized Set up and biological variability. The significant difference in the transition phase across the 2 groups requires further study.

  • 10. Frykberg, Gunilla E.
    et al.
    Thierfelder, Tomas
    Aberg, Anna Cristina
    Halvorsen, Kjartan
    KTH, Skolan för teknik och hälsa (STH), Medicinska sensorer, signaler och system (MSSS).
    Borg, Jorgen
    Hirschfeld, Helga
    Impact of stroke on anterior-posterior force generation prior to seat-off during sit-to-walk2012Ingår i: Gait & Posture, ISSN 0966-6362, E-ISSN 1879-2219, Vol. 35, nr 1, s. 56-60Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Force generation during sit-to-walk (STW) post-stroke is a poorly studied area, although STW is a common daily transfer giving rise to a risk of falling in persons with disability. The purpose of this study was to describe and compare strategies for anterior-posterior (AP) force generation prior to seat-off during the STW transfer in both subjects with stroke and in matched controls. During STW at self-selected speed, AP force data were collected by 4 force plates, beneath the buttocks and feet from eight subjects with stroke '(>6 months after onset) and 8 matched controls. Subjects with post-stroke hemiparesis and matched controls generated a similar magnitude of total AP force impulses (F-1.71 = 0.67; p = 0.42) beneath buttocks and feet prior to seat-off during STW. However, there were significant group differences in AP force impulse generation beneath the stance buttock (i.e. the non-paretic buttock in the stroke group), with longer duration (F-1.71 = 8.78; p <0.005), larger net AP impulse (F-1.71 = 6.76; p < 0.05) and larger braking impulse (F-1.71 = 7.24; p <0.05) in the stroke group. The total braking impulse beneath buttocks and feet was about 4.5 times larger in the stroke group than in the control group (F-1.71 = 8.84; p < 0.005). An intra-and inter-limb dys-coordination with substantial use of braking impulses was demonstrated in the stroke group. This motor strategy differed markedly from the smooth force interaction in the control group. These results might be important in the development of treatment models related to locomotion post-stroke.

  • 11.
    Frykberg, Gunilla
    et al.
    Uppsala University.
    Åberg, Anna Cristina
    The Swedish School of Sport and Health Sciences.
    Halvorsen, Kjartan
    The Swedish School of Sports and Health Sciences.
    Hirschfeld, Helga
    Karolinska Institute.
    Temporal characteristics of the sit-to-walk task in subjects with stroke and in controls: Preliminary results2007Ingår i: Proceedings of the 16th annual meeting of ESMAC, 2007Konferensbidrag (Refereegranskat)
  • 12.
    Halvorsen, Kjartan
    KTH, Skolan för teknik och hälsa (STH), Medicinsk teknik.
    Comments on "The equations of motion for a standing human reveal three mechanisms for balance" (A. Hof, Vol. 40, pp. 451-457)2010Ingår i: Journal of Biomechanics, ISSN 0021-9290, E-ISSN 1873-2380, Vol. 43, nr 16, s. 3244-3247Artikel i tidskrift (Refereegranskat)
  • 13.
    Halvorsen, Kjartan
    et al.
    The Swedish School of Sport and Health Sciences.
    Arndt, Anton
    Karolinska Institute.
    Lundberg, Arne
    Karolinska Institute.
    Estimating the directions of the talar and subtalar axes2007Ingår i: Proceedings of the International Society of Biomechanics XXI Congress, 2007Konferensbidrag (Refereegranskat)
  • 14.
    Halvorsen, Kjartan
    et al.
    The Swedish School of Sport and Health Sciences.
    Arndt, Anton
    The Swedish School of Sport and Health Sciences.
    Rosdahl, Hans
    The Swedish School of Sport and Health Sciences.
    Thorstensson, Alf
    The Swedish School of Sport and Health Sciences.
    Evaluation of three different models of the shoulder kinematics: application to kayak paddling2004Ingår i: Proceedings of ISB VIII International Symposium on the 3D Analysis of Human Movement, 2004Konferensbidrag (Refereegranskat)
  • 15.
    Halvorsen, Kjartan
    et al.
    KTH, Skolan för teknik och hälsa (STH), Medicinska sensorer, signaler och system (MSSS).
    Brechbühl, Simon
    ETH Zurich, Switzerland.
    Minimal set of markers for center of mass estimation in gravitational fall2009Ingår i: Proceedings of the ISB XXII Congress, 2009Konferensbidrag (Refereegranskat)
  • 16.
    Halvorsen, Kjartan
    et al.
    KTH, Skolan för teknik och hälsa (STH), Medicinsk teknik.
    Eriksson, Martin
    KTH, Skolan för teknik och hälsa (STH), Medicinsk teknik.
    Gullstrand, Lennart
    Swedish Sports Confederation.
    Acute Effects Of Reducing Vertical Displacement And Step Frequency On Running Economy2012Ingår i: Journal of Strength and Conditioning Research, ISSN 1064-8011, E-ISSN 1533-4287, Vol. 26, nr 8, s. 2065-2070Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This work studies the immediate effects of altering the vertical displacement of CoM (VD) and step frequency (SF) on the metabolic cost of level treadmill running at 16 km·h on sixteen male runners. Alterations of VD, SF and the product VD SF was induced using a novel feedback system which presents target and current values to the runner by visual or auditory display. Target values were set to 5 and 10% reductions from individual baseline values. Results were expressed as relative changes from baseline values.Alterations led to an increase in metabolic cost in most cases, measured as VO2 uptake per minute and kg body mass. Correlations were weak. Still, linear multiple regression revealed a positive coefficient (0.28) for the relationship between VD SF and VO2. Separate rank correlation tests showed negative correlation (τ = -0.19) between SF and VO2 and positive correlation (τ = -0.16) between VD and VO2. There is a coupling between VD and SF caused by the mechanics of running, hence isolated reduction of either factor was hard to achieve. The linear model also showed a negative coefficient for the relationship between the height of center of mass above ground (CoMh) and VO2.The effect size was small (multiple R-squared 0.07 and 0.12). Still the results indicate that reducing VD SF by reducing vertical displacement can have a positive effect on running economy, but a concurrent reduction in CoMh may reduce or diminish the positive effect. Mid- and long-term effects of altering the technique should also be studied.

  • 17.
    Halvorsen, Kjartan
    et al.
    KTH, Skolan för teknik och hälsa (STH), Medicinsk teknik.
    Eriksson, Martin
    KTH, Skolan för teknik och hälsa (STH), Medicinsk teknik.
    Gullstrand, Lennart
    Tinmark, Fredrik
    Nilsson, Johnny
    Minimal marker set for center of mass estimation in running2009Ingår i: Gait & Posture, ISSN 0966-6362, E-ISSN 1879-2219, Vol. 30, nr 4, s. 552-555Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The purpose was to study the validity of a recently proposed method [Forsell C, Halvorsen K. A method for determining minimal sets of markers for the estimation of center of mass, linear and angular momentum. journal of Biomechanics 2009;42(3):361-5] for estimating the trajectory of the whole-body center of mass (CoM) in the case of running at: velocities ranging from 10 to 22 km h(-1). The method gives an approximation to the CoM using the position of fewer markers on the body than the standard method of tracking each segment of the body. Fourteen male athletes participated. A standard method for determining the CoM from a model of 13 segments and using the position of 36 markers was used as reference method. Leave-one-out cross-validation revealed errors that decreased with increasing number of markers used in the approximative method. Starting from four markers, the error in absolute position of the CoM decreased from 15 mm to 3 mm in each direction. For the velocity of the CoM the estimation bias was neglectable, and the random error decreased from 0.15 to 0.05 m s(-1). The inter-subject and intra-subject variability in the estimated model parameters increased with increasing number of markers. The method worked well also when applied to running at velocities outside the range of velocities in the data used to determine the model parameters. The results indicate that a model using 10 markers represents a good trade-off between simplicity and accuracy, but users must take into account requirements of their specific applications.

  • 18.
    Halvorsen, Kjartan
    et al.
    KTH, Skolan för teknik och hälsa (STH), Medicinska sensorer, signaler och system (MSSS).
    Eriksson, Martin
    KTH, Skolan för teknik och hälsa (STH), Medicinska sensorer, signaler och system (MSSS).
    Nilsson, Johnny
    The Swedish School of Sport and Health Sciences.
    Tinmark, Fredrik
    The Swedish School of Sport and Health Sciences.
    Gullstrand, Lennart
    The Swedish Sport Confederation.
    The antero-posterior movement of the sacrum as an indicator of the antero-posterior movement of center of mass in running2011Ingår i: Proceedings of ECSS 16th Congress, 2011Konferensbidrag (Refereegranskat)
  • 19.
    Halvorsen, Kjartan
    et al.
    The Swedish School of Sport and Health Sciences.
    Frohm, Anna
    Karolinska Institute.
    Thorstensson, Alf
    The Swedish School of Sport and Health Sciences.
    The influence of declined support surface on the biomechanics of eccentric overload in squats2005Ingår i: Proceedings of the ISB XX Congress, 2005Konferensbidrag (Refereegranskat)
  • 20.
    Halvorsen, Kjartan
    et al.
    Swedish School of Sports and Health Sciences.
    Johnston, Christopher
    Swedish University of Agricultural Sciences.
    Back, Wim
    Utrecht University.
    Stokes, Virgil
    Uppsala University.
    Lanshammar, Håkan
    Uppsala University.
    Tracking the motion of hidden segments using kinematic constraints and Kalman filtering2008Ingår i: Journal of Biomechanical Engineering, ISSN 0148-0731, E-ISSN 1528-8951, Vol. 130Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Motion capture for biomechanical applications involves in almost all cases sensors or markers that are applied to the skin of the body segments of interest. This paper deals with the problem of estimating the movement of connected skeletal segments from 3D position data of markers attached to the skin. The use of kinematic constraints has been shown previously to reduce the error in estimated segment movement that are due to skin and muscles moving with respect to the underlying segment. A kinematic constraint reduces the number of degrees of freedom between two articulating segments. Moreover kinematic constraints can help reveal the movement of some segments when the 3D marker data otherwise are insufficient. Important cases include the human ankle complex and the phalangeal segments of the horse, where the movement of small segments is almost completely hidden from external observation by joint capsules and ligaments. This paper discusses the use of an extended Kalman filter for tracking a system of connected segments. The system is modeled using rigid segments connected by simplified joint models. The position and orientation of the mechanism are specified by a set of generalized coordinates corresponding to the mechanism's degrees of motion. The generalized coordinates together with their first time derivatives can be used as the state vector of a state space model governing the kinematics of the mechanism. The data collected are marker trajectories from skin-mounted markers, and the state vector is related to the position of the markers through a nonlinear function. The Jacobian of this function is derived The practical use of the method is demonstrated on a model of the distal part of the limb of the horse. Monte Carlo simulations of marker data for a two-segment system connected by a joint with three degrees of freedom indicate that the proposed method gives significant improvement over a method, which does not make use of the joint constraint, but the method requires that the model is a good approximation of the true mechanism. Applying the method to data on the movement of the four distal-most segments of the horse's limb shows good between trial consistency and small differences between measured marker positions and marker positions predicted by the model.

  • 21.
    Halvorsen, Kjartan
    et al.
    Swedish School of Sports and Health Sciences.
    Söderström, Torsten
    Uppsala University.
    Stokes, Virgil
    Uppsala University.
    Lanshammar, Håkan
    Uppsala University.
    Using an extended Kalman filter for rigid body pose estimation2005Ingår i: Journal of Biomechanical Engineering, ISSN 0148-0731, E-ISSN 1528-8951, Vol. 127, s. 475-483Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Rigid body pose is commonly represented as;he rigid body transformation from one (often reference) pose to another. This is usually computed for each frame of data without any assumptions or restrictions on the temporal change of the pose. The most common algorithm was proposed by Soderkvist and Wedin (1993, "Determining the Movements Of the Skeleton Using Well-configured Markers," J. Biomech., 26, pp. 1473-1477), and implies the assumption that measurement errors are isotropic and homogenous. This paper describes an alternative method based on a state space formulation and the application of an extended Kalman filter (EKF). State space models are formulated, which describe the kinematics of the rigid body. The state vector consists of six generalized coordinates (corresponding to the 6 degrees of freedom), and their first time derivatives. The state space models have linear dynamics, while the measurement function is a nonlinear relation between the state vector and the observations (marker positions). An analytical expression for the linearized measurement function is derived Tracking the rigid body motion using an EKF enables the use of a priori information on the measurement noise and type of motion to tune the filter. The EKF is time variant, which allows for a natural way of handling temporarily missing marker data. State updates are based on all the information available at each time step, even when data from fewer than three markers are available. Comparison with the method of Soderkvist and Wedin on simulated data showed a considerable improvement in accuracy with the proposed EKF method when marker data was temporarily missing. The proposed method offers an improvement in accuracy of rigid body pose estimation by incorporating knowledge of the characteristics of the movement and the measurement errors. Analytical expressions for the linearized system equations are provided, which eliminate the need for approximate discrete differentiation and which facilitate a fast implementation.

  • 22.
    Harringe, Marita
    et al.
    Karolinska Institute.
    Halvorsen, Kjartan
    Swedish School of Sports and Health Sciences.
    Renström, Per
    Karolinska Institute.
    Werner, Suzanne
    Karolinska Institute.
    Postural control measured as the center of pressure excursion in young female gymnasts with low back pain or lower extremity injury2008Ingår i: Gait & Posture, ISSN 0966-6362, E-ISSN 1879-2219, Vol. 28, s. 38-45Artikel i tidskrift (Refereegranskat)
  • 23.
    Jönhagen, Sven
    et al.
    Karolinska Institute.
    Halvorsen, Kjartan
    Swedish School of Sports and Health Sciences.
    Benoit, Daniel L
    Karolinska Institute.
    Muscle activation and length changes during two lunge exercises: implications for rehabilitation2009Ingår i: Scandinavian Journal of Medicine and Science in Sports, ISSN 0905-7188, E-ISSN 1600-0838, Scand J Med Sc Sports, Vol. 19, s. 561-568Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Eccentric exercises are commonly used as a treatment for various muscle and tendon injuries. During complex motions such as the forward lunge, however, it is not always clear which muscles may be contracting eccentrically and at what time. Because this exercise is used during rehabilitation, the purpose of this investigation was to determine what type of contractions take place during two different types of forward lunge and assess the implications for rehabilitation. Five experienced athletes performed five cycles for each of the walking and jumping forward lunges. Motion analysis was used to calculate the shortening or elongation of each muscle based on the change of position of their origin and insertion points during the lunge. Electromyography of the lateral hamstrings, rectus femoris and lateral gastrocnemius was combined with the muscle length change data to determine when isometric, concentric and eccentric activations occur during the lunge. Eccentric contractions in both the quadriceps and gastrocnemius were observed during the lunge. No hamstring eccentric contractions were found; however, the hamstrings showed isometric contractions during the first part of the stance phase.

  • 24. Nilsson, Johnny
    et al.
    Tinmark, Fredrik
    Halvorsen, Kjartan
    KTH, Skolan för teknik och hälsa (STH), Medicinska sensorer, signaler och system (MSSS).
    Arndt, Anton
    Kinematic, kinetic and electromyographic adaptation to speed and resistance in double poling cross country skiing2013Ingår i: European Journal of Applied Physiology, ISSN 1439-6319, E-ISSN 1439-6327, Vol. 113, nr 6, s. 1385-1394Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This study incorporated variations in speed and the horizontal resistance acting upon elite female skiers during double poling (DP) on a treadmill and specifically analyzed biomechanical adaptations to these variations. Whole body kinematics and pole force data were recorded and used to calculate the moment of force acting on the shoulder and elbow joints. Data were obtained with a 3D optoelectronic system using reflective markers at given anatomical landmarks. Forces along the long axis of the right pole were measured with a piezoelectric force transducer. Surface electrodes were used to record EMG activity in the rectus femoris, rectus abdominis, latissimus dorsi and triceps brachii muscles. In a first set of recordings, the participants double poled with zero elevation at five different speeds from 8 to 17 km h(-1). In a second set of recordings, horizontal resistance was added by weights (0.4-1.9 kg) attached to a pulley system pulling the skier posteriorly during DP at 14 km h(-1). Results showed increasing relative duration of the thrust phase with increasing resistance, but not with speed. Significant kinematic differences occurred with increase in both speed and resistance. The mean (+/- SD) horizontal force components ranged between 1.7 (+/- 1.3) and 2.8 (+/- 1.1) percent (%) bodyweight (BW) in the speed adaptation and 3.1 (+/- 0.6) and 4.0 (+/- 1.3) % BW in the adaptation to horizontal resistance. Peak muscle activity showed a central to peripheral (proximo-distal) activation sequence. The temporal cycle phase pattern in the adaptation to speed and horizontal resistance differed.

  • 25.
    Sturm, Dennis
    et al.
    KTH, Skolan för teknik och hälsa (STH), Medicinska sensorer, signaler och system (MSSS) (Stängd 20130701).
    Yousaf, Khurram
    KTH, Skolan för teknik och hälsa (STH), Medicinska sensorer, signaler och system (MSSS) (Stängd 20130701).
    Brodin, Lars-Åke
    KTH, Skolan för teknik och hälsa (STH), Medicinsk teknik.
    Halvorsen, Kjartan
    KTH, Skolan för teknik och hälsa (STH), Medicinska sensorer, signaler och system (MSSS) (Stängd 20130701). Uppsala University, Uppsala, Sweden .
    Wireless kayak on-water ergometry - Part 1: Paddle blade force2013Ingår i: Sports Technology, ISSN 1934-6182, E-ISSN 1934-6190, Vol. 6, nr 1, s. 29-42Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The aim of this work was to present a new wireless paddle force measurement system and to evaluate this measurement system. The system is redeveloped from a previous design and includes inertial motion sensors, which allows for the movement and inertia of the paddle to be taken into account. The system consists of two sensor nodes, designed for quick attachment to virtually any kayak paddle and an Android phone or tablet. Each sensor node measures the bending of the shaft in one plane. We derive the expressions necessary for computing the force on the paddle blade in two directions, ignoring the force in the direction of the shaft. Two different schemes for calibrating the system are presented. The accuracy and reliability of the system is evaluated in a laboratory setting using a material testing machine. An average error of 0.4% can be achieved for force measurements following directly after calibration. When the sensors are removed and reattached between calibration and measurements, average error between loading and measured force increased to 2.0% (linear model) and 1.8% (quadratic model). The limits of agreement depend on the position of the sensor nodes along the shaft and the feather angle if transverse sensitivity of the sensors is used to determine two-dimensional force on the paddle blade. On-water stroke force is presented, averaged over 10 strokes for each side with force levels >200 N to show the applicability of the study. The accuracy of the measurement is affected by the calibration method, placement of the paddle nodes and the shaft's properties.

  • 26.
    Sturm, Dennis
    et al.
    KTH, Skolan för teknik och hälsa (STH), Medicinska sensorer, signaler och system (MSSS).
    Yousaf, Khurram
    KTH, Skolan för teknik och hälsa (STH), Medicinska sensorer, signaler och system (MSSS).
    Eriksson, Martin
    KTH, Skolan för teknik och hälsa (STH), Medicinska sensorer, signaler och system (MSSS).
    Tornberg, Åsa B.
    Halvorsen, Kjartan
    KTH, Skolan för teknik och hälsa (STH), Medicinska sensorer, signaler och system (MSSS).
    Validation of a novel wireless Force Measurement System for Kayak Paddle ShaftsManuskript (preprint) (Övrigt vetenskapligt)
  • 27.
    Sturm, Dennis
    et al.
    KTH, Skolan för teknik och hälsa (STH), Medicinska sensorer, signaler och system (MSSS).
    Yousaf, Khurram
    KTH, Skolan för teknik och hälsa (STH), Medicinska sensorer, signaler och system (MSSS).
    Halvorsen, Kjartan
    KTH, Skolan för teknik och hälsa (STH), Medicinska sensorer, signaler och system (MSSS).
    Eriksson, Martin
    KTH, Skolan för teknik och hälsa (STH), Medicinska sensorer, signaler och system (MSSS).
    Håkansson, Paul
    Lund University.
    Segerström, Åsa
    Lund University.
    Measuring Kayak Paddle Performance with Wireless Strain Sensors on the Shaft: A Validation Study2011Konferensbidrag (Refereegranskat)
  • 28.
    Tinmark, Fredrik
    et al.
    The Swedish School of Sport and Health Sciences.
    Hellström, John
    The Swedish School of Sport and Health Sciences.
    Halvorsen, Kjartan
    The Swedish School of Sport and Health Sciences.
    Thorstensson, Alf
    The Swedish School of Sport and Health Sciences.
    Analysis of elite golfers' kinematic sequence in full-swing and partial swing shots2009Ingår i: Proceedings of ISBS 27 International Conference on Biomechanics in Sports, 2009Konferensbidrag (Refereegranskat)
    Abstract [en]

    Proximal-to-distal sequencing (PDS) has been observed in full-swing golf shots as in most throwing and striking skills, where the main goal is to maximize speed in the most distal segment of an open-link system (Zheng et al., 2007). Although PDS primarily is associated with mechanical advantage when the speed requirement is high, this temporal order has also been found and ascribed various merits in relatively slow multi-joint movements (Furuya & Kinoshita, 2007). However, no research to date has examined the sequencing pattern in partial golf shots to submaximal distances. The purpose here was to investigate whether PDS is a common characteristic also in partial swing shots of skilled golf players. METHODS: A total of 47 golfers were investigated, 11 male tournament professionals, 23 male amateurs (HCP 0 ± 2 strokes), and 13 female amateurs (HCP -2 ± 2 strokes) performed partial shots with a wedge to targets at three discrete distances (40, 55 and 70 m), and full-swing shots with a five iron as well as a driver in the same direction for maximal distance. Pelvis, upper torso, and hand movement were recorded in 3D with an electromagnetic tracking system (Polhemus) at 240 Hz. The magnitude of the resultant angular velocity vector of each segment was used to examine the sequencing pattern and the angular speed of segment motions. Movement onset, peak amplitude and time for peak amplitude were analyzed in separate repeated-measure ANOVAs with pre-planned Bonferroni corrected pairwise comparisons.

  • 29. Tinmark, Fredrik
    et al.
    Hellström, John
    Halvorsen, Kjartan
    KTH, Skolan för teknik och hälsa (STH), Medicinsk teknik.
    Thorstensson, Alf
    Elite golfers' kinematic sequence in full-swing and partial-swing shots2010Ingår i: SPORT BIOMECH, ISSN 1476-3141, Vol. 9, nr 4, s. 236-244Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The aim of this study was to investigate whether kinematic proximal-to-distal sequencing (PDS) and speed-summation are common characteristics of both partial and full-swing shots in golf players of different skill levels and genders. A total of 45 golfers participated, 11 male tournament professionals, 21 male and 13 female elite amateurs. They performed partial shots with a wedge to targets at three submaximal distances, 40, 55 and 70m, and full-swing shots with a 5 iron and a driver for maximal distance. Pelvis, upper torso and hand movements were recorded in 3D with an electromagnetic tracking system (Polhemus Liberty) at 240Hz and the magnitude of the resultant angular velocity vector of each segment was computed. The results showed a significant proximal-to-distal temporal relationship and a concomitant successive increase in maximum (peak) segment angular speed in every shot condition for both genders and levels of expertise. A proximal-to-distal utilization of interaction torques is indicated. Using a common PDS movement strategy in partial and full-swing golf shots appears beneficial from mechanical and control points of view and could serve the purpose of providing both high speed and accuracy.

  • 30.
    Tinmark, Fredrik
    et al.
    The Swedish School of Sport and Health Sciences.
    Hellström, John
    Örebro University.
    Thorstensson, Alf
    The Swedish School of Sport and Health Sciences.
    Halvorsen, Kjartan
    KTH, Skolan för teknik och hälsa (STH), Medicinska sensorer, signaler och system (MSSS).
    Contributions to endpoint velocity in a bimanual striking task2011Ingår i: Proceedings of ISB XXIII Congress, 2011Konferensbidrag (Refereegranskat)
  • 31.
    Zetterberg, Lena
    et al.
    Uppsala University.
    Aquilonius, Sten-Magnus
    Uppsala University.
    Lindmark, Birgitta
    Uppsala University.
    Lundström, Erik
    Uppsala University.
    Stokes, Virgil
    Uppsala University.
    Färnstrand, Catarina
    Uppsala University.
    Halvorsen, Kjartan
    The Swedish School of Sport and Health Sciences.
    Objective assessment in cervical dystonia2004Ingår i: Proceedings from ESMAC 13th Annual Meeting of European Society of Movement Analysis of Adult and Children, 2004Konferensbidrag (Refereegranskat)
  • 32.
    Zetterberg, Lena
    et al.
    Uppsala University.
    Halvorsen, Kjartan
    Swedish School of Sports and Health Sciences.
    Färnstrand, Catarina
    Uppsala University.
    Aquilonius, Sten-Magnus
    Uppsala University.
    Lindmark, Birgitta
    Uppsala University.
    Physiotherapy in cervical dystonia: six experimental single-case studies2008Ingår i: Physiotherapy Theory and Practice, ISSN 0959-3985, E-ISSN 1532-5040, Vol. 24, nr 4, s. 275-290Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The aim of the study was to explore the outcome of a physiotherapy program targeted to improve the quality of life of people with cervical dystonia (CD) by reducing pain, improving awareness of postural orientation, increasing muscle strength, and reducing the effort of moving the head and neck. In six single case studies, the primary outcome measure for each case was the Cervical Dystonia Questionnaire (CDQ) to measure the impact of the program on the individuals' quality of life. Secondary outcome measures were identified for the different components of the physiotherapy program: Visual Analogue Scale (pain); Postural Orientation Index (postural orientation awareness); and Movement Energy Index (effort of moving head and neck). Each of the cases had the severity of their problems scored on the Toronto Western Spasmodic Torticollis Scale. The study period was 26 weeks: 2 weeks' baseline period, 4 weeks' treatment period, and 20 weeks' follow-up. All measures except the Movement Energy Index (MEI) and CDQ-24 were taken three times per week for the first 6 weeks of the study and then once at 3 and 6 months. The MEI was taken once a week during the pretreatment and the treatment periods and during the first 2 weeks of follow-up and also after 3 and 6 months of follow-up. The CDQ-24 was taken once in the pretreatment period, once after completion of treatment, once 2 weeks after treatment, and once at 3 and 6 months of follow-up. Five of the six case studies reported an increase in quality of life at 6-month follow-up, as measured on the CDQ-24. Three of the six cases reported a reduction in pain and severity of the dystonia and had improved scores on the postural orientation measure at 6-month follow-up. All six patients had a reduction in the movement energy scores, but this was not significant. The outcomes of the six case studies would suggest that further investigation is required to show the effectiveness of physiotherapy programs in the management of CD.

  • 33.
    Zetterberg, Lena
    et al.
    Uppsala University.
    Halvorsen, Kjartan
    Swedish School of Sports and Health Sciences.
    Färnstrand, Catarina
    Uppsala University.
    Lundström, Erik
    Uppsala University.
    Lindmark, Birgitta
    Uppsala University.
    Aquilonius, Sten-Magnus
    Uppsala University.
    Objective assessment of cervical dystonia: a pilot study2005Ingår i: Acta Neurologica Scandinavica, ISSN 0001-6314, E-ISSN 1600-0404, Vol. 112, nr 4, s. 248-253Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Objectives - The aims were to characterize the movements in cervical dystonia (CD) by using an estimate of the mechanical power and work involved in the movements and to describe this through a movement energy index (MEI). Materials and methods - The subjects (patients n = 6, controls n = 6) were seated in front of a screen with a laser pointer attached to a headband while they performed standardized movements. A three-dimensional motion capture system was used and a test-retest was performed. Results - The mean value of MEI was significantly higher for the patients than for the controls. There was no significant difference between MEI from test to retest for the patients but there was a significant difference between MEI from test to retest for the controls. Conclusion - This study suggests that MEI could be a useful measure for the quantification of movement dysfunction in CD and thus an objective outcome measure in comparison of different therapies.

  • 34.
    Åberg, Anna Cristina
    et al.
    Swedish School of Sports and Health Sciences.
    Frykberg, Gunilla
    Uppsala University.
    Halvorsen, Kjartan
    The Swedish School of Sport and Health Sciences, Stockholm, Sweden.
    Medio-lateral stability of sit-to-walk performance in older individuals with and without fear of falling2010Ingår i: Gait & Posture, ISSN 0966-6362, E-ISSN 1879-2219, Vol. 31, nr 4, s. 438-443Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Most falls in older people are due to loss of balance during everyday locomotion, e.g., when initiating walking from sitting; sit-to-walk (STW). It has been considered that the broader stride width in walking that is seen in many people with fear of falling (FoF) does not increase stability, but could be predictive of future falls because of increased medio-lateral (ML) velocity of the body centre of mass (CoM). This study was aimed to examine step-, velocity- and stability-related parameters, focusing on ML stability, in STW performance of people with and without FoF. Ten subjects with FoF and 10 matched controls, aged >= 70 years, were included. Kinematic and kinetic data were collected in a laboratory. Stability parameters were calculated from a formula implying that the vertical projection of the CoM extrapolated by adding its velocity times a factor root l/g (height of inverted pendulum divided by gravity) should fall within the base of support (BoS). A related spatial margin of stability (SMoS), defined as the minimum distance from the extrapolated CoM (XCoM) to the boundaries of the BoS, was also calculated. In the phase 'seat-off-second-toe-off, the FoF group had significantly (p < 0.05) shorter and broader steps, lower forward but similar ML CoM velocity, and broader CoM and XCoM widths. The FoF group therefore exhibited a disproportionately large sideways velocity compared to the controls. This indicates that STW may be a hazardous transfer for older people with FoF, which should be relevant in assessment and training aimed at preventing falls.

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