Eccentrically-Induced Fatigue in Voluntary Muscle Performance: the Effect of Muscle Length and Contraction Type

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 RTD, 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.