Acute cross-education effect on force production and central/peripheral responses to unilateral eccentric and concentric resistance exercise in elbow flexors.

Abstract

The cross-education effect (CE) is the transference of neuromuscular adaptations from a single exercised limb to the contralateral nonexercised limb, which seems to differ between exercise modalities. We compared the acute CE of unilateral eccentric (ECC) and concentric (CONC) resistance exercises on neuromuscular function and force production changes of the nonexercised elbow flexors (EF). Healthy men were randomly allocated into ECC (n = 15) or CONC (n = 15) groups. The effects of control (CTRL_CONC or CTRL_ECC: 30 min of sitting) and exercise conditions (5 sets × 10 repetitions at 80% of either ECC or CONC 1-repetition maximum) of the dominant EF were measured. Maximal voluntary isometric contraction (MVIC), rate of torque development (RTD), corticospinal excitability (CSE), voluntary activation (VA), and peripheral factors were measured before and immediately after CTRL_CONC/CTRL_ECC or CONC/ECC. Surface electromyography amplitude integral (sEMG_i) from the biceps brachii (BB) muscle was monitored during exercise. Physical-mental demands (NASA-TLX) were assessed after exercise. ECC performed 26.2% greater exercise volume than CONC (P = 0.01). ECC showed lesser BB sEMG_i (P = 0.04) than CONC in the exercised EF; however, it induced threefold greater irradiated sEMG_i to the nonexercised BB than CONC (P = 0.04) during exercise. NASA-TLX was unchanged (P = 0.81). The nonexercised EF maintained MVIC, VA, cortical silent period, and peripheral factors after ECC and CONC (P > 0.05), but lower RTD was observed after ECC (23.5%-29.4%; P < 0.05) and CONC (10.8%; P < 0.05). Lower CSE at 75% of MVIC occurred after ECC (-17%; P = 0.02) compared with CTRL_ECC, which was correlated to RTD decreases (r = 0.45-0.56, P = 0.02-0.04). ECC induces acute contralateral reductions in CSE that are associated with decreases in RTD.NEW & NOTEWORTHY Unilateral eccentric and concentric resistance exercises can modulate the neuromuscular response differently, which influences the transference of the force production capacity to the contralateral nonexercised muscle. Unilateral eccentric exercise induced decreases in corticospinal excitability with associated reductions in the early phase of the rate of torque development, which differs from the changes observed after concentric exercise. Thus, both exercise modalities seem to change the excitability differently.