Less fatiguability in eccentric than concentric repetitive maximal muscle contractions.

Abstract

Changes in elbow flexion torque and biceps brachii electromyogram (EMG) activity over 30 repetitive maximal voluntary concentric-only (CON-only), eccentric-only (ECC-only), and alternative concentric and eccentric (CON-ECC, 30 concentric + 30 eccentric) contractions were examined to compare their muscle fatigue profiles. Fifteen healthy young men performed CON-only, ECC-only and CON-ECC in their maximal effort between 10° and 100° elbow flexion on an isokinetic dynamometer at an angular velocity of 30°/s with a 3-s rest between contractions in a randomised order with ≥ 3days between conditions. Changes in torque and EMG over the repeated contractions and maximal voluntary isometric contraction (MVC-ISO) torque with EMG before the first contraction and immediately after the last contraction were compared among conditions by two-way repeated measures analysis of variance. The torque decreased (p < 0.01) from the first to 30th contraction in CON-only (-49.5 ± 11.0%), ECC-only (-32.2 ± 7.4%), and concentric (-62.3 ± 8.7%) as well as eccentric phase (-58.9 ± 9.3%) in CON-ECC (-46.0 ± 12.3% overall). The magnitude of the decrease in the torque was greater (p < 0.01) for the CON-only than ECC-only, and the concentric than an eccentric phase in the CON-ECC. However, MVC-ISO torque decreased (p < 0.01) similarly after CON-only (-42.9 ± 13.8%) and ECC-only (-40.1 ± 9.2%), which was smaller (p < 0.01) than CON-ECC (-56.8 ± 9.2%). EMG over contractions decreased (p < 0.01) for all conditions similarly from the first to the last contraction (-28.5 ± 26.8%), and EMG in MVC-ISO also decreased similarly for all conditions (-24.7 ± 35.8%). These results suggest greater fatigue resistance in repetitive maximal eccentric than concentric contractions, but the fatigue assessed by MVC-ISO does not show it.