Time-Course of Neuromuscular Changes during and after Maximal Eccentric Contractions

Abstract

This study tested the relationship between the magnitude of muscle damage and both central and peripheral modulations during and after eccentric contractions of plantar flexors. Eleven participants performed 10 sets of 30 maximal eccentric contractions of the plantar flexors at 45°·s(-1). Maximal voluntary torque, evoked torque (peripheral component) and voluntary activation (central component) were assessed before, during, immediately after (POST) and 48 h after (48 h) the eccentric exercise. Voluntary eccentric torque progressively decreased (up to -36%) concomitantly to a significant alteration of evoked torque (up to -34%) and voluntary activation (up to -13%) during the exercise. Voluntary isometric torque (-48 ± 7%), evoked torque (-41 ± 14%) and voluntary activation (-13 ± 11%) decreased at POST, but only voluntary isometric torque (-19 ± 6%) and evoked torque (-10 ± 18%) remained depressed at 48 h. Neither changes in voluntary activation nor evoked torque during the exercise were related to the magnitude of muscle damage markers, but the evoked torque decrement at 48 h was significantly correlated with the changes in voluntary activation (r = -0.71) and evoked torque (r = 0.77) at POST. Our findings show that neuromuscular responses observed during eccentric contractions were not associated with muscle damage. Conversely, central and peripheral impairments observed immediately after the exercise reflect the long-lasting reduction in force-generating capacity.

Keywords: central activation ratio; evoked torque; muscle damage; plantar flexors; voluntary activation level.

Figure 1

Example of torque traces for maximal voluntary isometric contractions before and immediately after the exercise (A) and for maximal voluntary eccentric contractions during the exercise (B). Double arrows represent paired stimulations superimposed to contractions (superimposed doublet) and evoked on the resting muscle after isometric contractions (potentiated doublet) or during a passive dorsiflexion cycle (lengthening doublet). Superimposed doublets are enlarged in the top right corner of each panel. Two-way arrows correspond to superimposed torques between the evoked torque and voluntary isometric peak torque (A) or extrapolated eccentric torque (B).

Figure 2

Relative changes from baseline (mean ± SD) for voluntary isometric peak torque, potentiated evoked torque and voluntary activation level (VAL) after the exercise. ^*Significantly different from baseline (^* < 0.05; ^*** < 0.001).

Figure 3

Relative changes from set 1 (mean ± SD) for mean voluntary torque, lengthening evoked torque and central activation ratio (CAR) during the eccentric exercise. ^*Significantly different from set 1 (^* < 0.05; ^** < 0.01; ^*** < 0.001).