Effects of unilateral eccentric versus concentric training of nonimmobilized arm during immobilization

Introduction The present study tested the hypothesis that eccentric training (ET) of nonimmobilized arm would attenuate negative effects of immobilization and provide greater protective effects against muscle damage induced by eccentric exercise after immobilization, when compared with concentric training (CT). Methods Sedentary young men were placed to ET, CT, or control group (n = 12 per group), and their nondominant arms were immobilized for 3 wk. During the immobilization period, the ET and CT groups performed five sets of six dumbbell curl eccentric-only and concentric-only contractions, respectively, at 20%-80% of maximal voluntary isometric contraction (MVCiso) strength over six sessions. MVCiso torque, root-mean square (RMS) of electromyographic activity during MVCiso, and bicep brachii muscle cross-sectional area (CSA) were measured before and after immobilization for both arms. All participants performed 30 eccentric contractions of the elbow flexors (30EC) by the immobilized arm after the cast was removed. Several indirect muscle damage markers were measured before, immediately after, and for 5 d after 30EC. Results ET increased MVCiso (17% ± 7%), RMS (24% ± 8%), and CSA (9% ± 2%) greater (P \u3c 0.05) than CT (6% ± 4%, 9% ± 4%, 3% ± 2%) for the trained arm. The control group showed decreases in MVCiso (-17% ± 2%), RMS (-26% ± 6%), and CSA (-12% ± 3%) for the immobilized arm, but these changes were attenuated greater (P \u3c 0.05) by ET (3% ± 3%, -0.1% ± 2%, 0.1% ± 0.3%) than CT (-4% ± 2%, -4% ± 2%, -1.3% ± 0.4%). Changes in all muscle damage markers after 30EC were smaller (P \u3c 0.05) for the ET and CT than the control group, and ET than the CT group (e.g., peak plasma creatine kinase activity: ET, 860 ± 688 IU L-1; CT, 2390 ± 1104 IU L-1; control, 7819 ± 4011 IU L-1). Conclusions These results showed that ET of the nonimmobilized arm was effective for eliminating the negative effects of immobilization and attenuating eccentric exercise-induced muscle damage after immobilization