Abstract
Research background and hypothesis. We hypothesized that eccentric exercise (EE) would induce muscle fatigue and damage, which are dependent not only on muscle length tested but and on contraction type (eccentric vs. concentric vs. isometric) as well.Research aim was to test the hypothesis.Research methods. Healthy untrained men (mean ± SD: age = 24.8 ± 3.7 years, n = 10) performed 10 series of 12 repetitions of eccentric knee contractions at 160 deg/s. The maximal voluntary isometric contraction force (MVC) of the quadriceps muscle, the maximal rate of torque development (RTD) and isokinetic torque at 30 deg/s were established before and after EE. All measures were performed at different knee angles. Besides, the EMG of the quadriceps muscle was measured.Research results showed a significant change in absolute values of RTD after EE (before EE: 3695 ± 803 N∙m/s and 2360 ± 695 N∙m/s at SL and LL respectively; after EE: 2574 ± 843 N∙m/s and 1517 ± 476 N∙m/s at SL and LL respectively). A significant difference between EMG (rms) in MVC was found after EE at LL and SL, i. e. in v.lateralis 0.32 ± 0.12 mV and 0.24 ± 0.1 mV and in r.femoris 0.25 ± 0.11 mV and 0.17 ± 0.07 mV respectively. All criteria of voluntary performance changed significantly after EE except for R TD, i.e. it increased after EE.Discussion and conclusions. We observed more changes in isokinetic torque at shorter muscle length after eccentric exercise-induced muscle fatigue and damage. The changes in MVC and RTD after eccentric exercise did not depend on the length of the muscle tested. Besides, relative RTD did not change after exercise.Keywords: eccentric, concentric and isometric contraction; muscle fatigue and damage; muscle length, muscle force; rate of muscle torque development.
Highlights
The well documented symptoms of exerciseinduced muscle damage (EIMD) include prolonged impairment of muscle function as measured in voluntary and electrically-induced contractions (Warren et al, 1999; Byrne et al, 2004; Skurvydas et al, 2006)
The changes in maximal voluntary isometric contraction force (MVC) and rate of torque development (RTD) after eccentric exercise did not depend on the length of the muscle tested
The changes in isometric MVC and RTD after eccentric exercise did not depend on the length of the muscle tested
Summary
The well documented symptoms of exerciseinduced muscle damage (EIMD) include prolonged impairment of muscle function as measured in voluntary and electrically-induced contractions (Warren et al, 1999; Byrne et al, 2004; Skurvydas et al, 2006). It is generally agreed that there are two prominent signs of damage in the muscle immediately after it has been subjected to a series of eccentric contractions These are the presence of disrupted force-bearing structures and damage to excitation-contraction coupling system (Warren et al, 1999; Proske, Morgan, 2001). It has been established that muscle damaging exercise decreases muscle isometric, concentric and eccentric contraction force (Warren et al, 1999; Michaut et al, 2003; Byrne et al, 2004; Skurvydas et al, 2006; Hubal et al, 2008), rightward shift in the optimum joint angle for voluntary isometric (Proske, Morgan, 2001; Philipou et al, 2004; McHugh, Tetro, 2003; Chen et al, 2007) as well concentric strength The following issues, have not been cleared up, yet, namely: 1) what are length-dependent changes in quadriceps muscle torque during isometric as well as in concentric contraction, 2) are there differences between changes in maximal voluntary isometric contraction torque (MVC) and rate of torque development (RTD), what is the relationship between the changes in different muscle mechanical characteristics after muscle damaging eccentric exercise? The primary aim of the present study was to clarify these issues
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