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Muscle-fiber conduction velocity during concentric and eccentric actions on a flywheel exercise device
Karolinska Institutet.ORCID iD: 0000-0003-3470-5175
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2006 (English)In: Muscle and Nerve, ISSN 0148-639X, E-ISSN 1097-4598, Vol. 34, no 2, 169-177 p.Article in journal (Refereed) Published
Abstract [en]

A gravity-independent flywheel exercise device (FWED) has been proven effective as a countermeasure to loss of strength and muscle atrophy induced by simulated microgravity. This study assessed muscle-fiber conduction velocity (CV) and surface EMG instantaneous mean power spectral frequency (iMNF) during brief bouts of fatiguing concentric (CON) and eccentric (ECC) exercise on a FWED in order to identify electromyographic (EMG) variables that can be used to provide objective indications of muscle status when exercising with a FWED. Multichannel surface EMG signals were recorded from vastus lateralis and medialis muscles of nine men during: (1) isometric, 60-s action at 50% of maximum voluntary action (MVC); (2) two isometric, linearly increasing force ramps (0-100% MVC); and (3) dynamic CON/ECC coupled actions on the FWED. Muscle-fiber CV and iMNF were computed over time during the three tasks. During ramps, CV, but not iMNF, increased with force (P < 0.001). Conduction velocity and iMNF decreased with the same normalized rate of change in constant-force actions. During CON/ECC actions, the normalized rate of change over time was larger for CV than iMNF (P < 0.05). These results suggest that, during fatiguing, dynamic, variable-force tasks, changes in CV cannot be indirectly inferred by EMG spectral analysis. This underlines the importance of measuring both CV and spectral variables for muscle assessment in dynamic tasks.

Place, publisher, year, edition, pages
2006. Vol. 34, no 2, 169-177 p.
Keyword [en]
concentric and eccentric actions, flywheel ergometer, muscle-fiber conduction velocity, surface electromyography
National Category
Physiology
Identifiers
URN: urn:nbn:se:kth:diva-45793DOI: 10.1002/mus.20574ISI: 000239397800006PubMedID: 16688721OAI: oai:DiVA.org:kth-45793DiVA: diva2:452922
Note
QC 20111102Available from: 2011-10-31 Created: 2011-10-31 Last updated: 2017-12-08Bibliographically approved
In thesis
1. Acute and early chronic responses to resistance exercise using flywheel or weights
Open this publication in new window or tab >>Acute and early chronic responses to resistance exercise using flywheel or weights
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Resistance exercise using weights typically offers constant external load during coupled shortening (concentric) and lengthening (eccentric) muscle actions in sets of consecutive repetitions until failure. However, the constant external load and the inherent capability of skeletal muscle to produce greater force in the eccentric compared with the concentric action, would infer that most actions are executed with incomplete motor unit involvement. In contrast, use of the inertia of flywheels to generate resistance allows for maximal voluntary force to be produced throughout the concentric action, and for brief episodes of greater eccentric than concentric loading, i.e. “eccentric overload”. Thus, it was hypothesized that acute flywheel resistance exercise would induce greater motor unit and muscle use, and subsequent fatigue, compared with traditional weight stack/free weight resistance exercise. Furthermore, it was hypothesized that flywheel training would induce more robust neuromuscular adaptations compared with training using weights.

A total of 43 trained and untrained men were investigated in these studies. Knee extensor muscle activation, fatigue response and muscle use were assessed during exercises by recording electromyographic signals and by means of functional magnetic resonance imaging, respectively. Flywheel resistance exercise provoked maximal or near maximal muscle activation from the first repetition, induced robust fatigue, and prompted more substantial motor unit and muscle use than weight stack/free weight resistance exercise in both novice and resistance trained men. Both prior to and following five weeks of unilateral knee extension training, the eccentric muscle activation was greater with flywheel than weight stack training. Furthermore, weight stack training generated greater increases of dynamic strength and neural adaptations, while flywheel training generated more prominent hypertrophy of individual quadriceps muscles and greater improvement of maximal isometric strength.

Hence, due to the preferential metabolic cost of the concentric rather than eccentric actions, the maximal activation through the entire range of the concentric action within each repetition of a set during flywheel resistance exercise probably evoked the marked fatigue, and prompted more substantial muscle use than resistance exercise using weights. Furthermore, while any cause-effect relationship remains to be determined, results of the present study suggest that brief episodes of “eccentric overload” amplify muscular adaptations following concentric-eccentric resistance training.

Place, publisher, year, edition, pages
Östersund: Mittuniversitetet, 2010. 50 p.
Keyword
electromyography, flywheel, magnetic resonance imaging, resistance exercise
National Category
Physiology
Identifiers
urn:nbn:se:kth:diva-48477 (URN)
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Note
QC 20111206Available from: 2011-12-07 Created: 2011-11-18 Last updated: 2011-12-07Bibliographically approved

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