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Quadriceps muscle use in the flywheel and barbell squat
Karolinska Institutet, Department of Physiology and Phamacology.
2011 (English)In: Aviation, Space and Environmental Medicine, ISSN 0095-6562, Vol. 82, no 1, 13-19 p.Article in journal (Refereed) Published
Abstract [en]

Background: Resistance exercise has been proposed as an aid to counteract quadriceps muscle atrophy in astronauts during extended missions in Orbit. While space authorities have advocated the squat exercise should be prescribed, no exercise system suitable for in-flight use has been validated with regard to quadriceps muscle use. We compared muscle involvement in the terrestrial “gold standard” squat using free weights and a non-gravity dependent flywheel resistance exercise device aimed at use in space. Methods: Ten strength-trained men performed five sets of 10 repetitions using the Barbell Squat (BS; 10 repetition maximum) or Flywheel Squat (FS; each repetition maximal), respectively. Functional magnetic resonance imaging (MRI) and surface electromyography (EMG) techniques assessed quadriceps muscle use. Exercise-induced contrast shift of MR images was measured by means of transverse relaxation time (T2). EMG root mean square (RMS) was measured during concentric (CON) and eccentric (ECC) actions and normalized to EMG RMS determined during maximal voluntary contraction. Results: The quadriceps muscle group showed greater exercise-induced T2 increase following FS compared with BS. Among individual muscles, the rectus femoris displayed greater T2 increase with FS (+24±14%) than BS (+8±4%). Normalized quadriceps EMG showed no difference across exercise modes. Discussion: Collectively, the results of this study suggest that quadriceps muscle use in the squat is comparable, if not greater, with flywheel compared with free weight resistance exercise. Data appears to provide support for use of flywheel squat resistance exercise as a countermeasures adjunct during spaceflight.

Place, publisher, year, edition, pages
Alexandria, VA: Aerospace Medical Association , 2011. Vol. 82, no 1, 13-19 p.
Keyword [en]
functional MRI, inertial resistance, knee extension, spaceflight, surface EMG
National Category
Physiology Sport and Fitness Sciences
URN: urn:nbn:se:kth:diva-42166DOI: 10.3357/ASEM.2867.2011ISI: 000285903500004PubMedID: 21235100OAI: diva2:446092
QC 20111116Available from: 2011-10-06 Created: 2011-10-06 Last updated: 2011-12-07Bibliographically 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.
electromyography, flywheel, magnetic resonance imaging, resistance exercise
National Category
urn:nbn:se:kth:diva-48477 (URN)
QC 20111206Available from: 2011-12-07 Created: 2011-11-18 Last updated: 2011-12-07Bibliographically approved

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