Article

Comparison in muscle damage between maximal voluntary and electrically evoked isometric contractions of the elbow flexors

School of Exercise, Biomedical and Health Sciences, Edith Cowan University, 270 Joondalup Drive, Joondalup, WA 6027, Australia.
Arbeitsphysiologie (Impact Factor: 2.19). 05/2011; 112(2):429-38. DOI: 10.1007/s00421-011-1991-3
Source: PubMed

ABSTRACT

This study compared between maximal voluntary (VOL) and electrically stimulated (ES) isometric contractions of the elbow flexors for changes in indirect markers of muscle damage to investigate whether ES would induce greater muscle damage than VOL. Twelve non-resistance-trained men (23-39 years) performed VOL with one arm and ES with the contralateral arm separated by 2 weeks in a randomised, counterbalanced order. Both VOL and ES (frequency 75 Hz, pulse duration 250 μs, maximally tolerated intensity) exercises consisted of 50 maximal isometric contractions (4-s on, 15-s off) of the elbow flexors at a long muscle length (160°). Changes in maximal voluntary isometric contraction torque (MVC), range of motion, muscle soreness, pressure pain threshold and serum creatine kinase (CK) activity were measured before, immediately after and 1, 24, 48, 72 and 96 h following exercise. The average peak torque over the 50 isometric contractions was greater (P < 0.05) for VOL (32.9 ± 9.8 N m) than ES (16.9 ± 6.3 N m). MVC decreased greater and recovered slower (P < 0.05) after ES (15% lower than baseline at 96 h) than VOL (full recovery). Serum CK activity increased (P < 0.05) only after ES, and the muscles became more sore and tender after ES than VOL (P < 0.05). These results showed that ES induced greater muscle damage than VOL despite the lower torque output during ES. It seems likely that higher mechanical stress imposed on the activated muscle fibres, due to the specificity of motor unit recruitment in ES, resulted in greater muscle damage.

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    • "Chapman et al. 2008; Lau and Nosaka 2011). In Fig. 4, an example from our laboratory in which 60 maximal voluntary eccentric contractions of the elbow Xexors from a Xexed (90°) to a fully extended position (»180°) were performed by similar subjects to those used in the ES study (Jubeau et al. 2011) is shown. The changes in the MVC strength, muscle soreness and CK activity are similar to those following ES-evoked isometric contractions, but greater than those following maximal voluntary isometric contractions. "
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