Neuromuscular fatigue profile in endurance-trained and power-trained athletes

Purpose: This study examined the effects of training background on the relationship between the neuromuscular fatigue profile and maximal voluntary torque production in isometric, concentric, and eccentric contraction modes. Methods: Before and after three sets of 31 isokinetic concentric knee extensions at 60°·s-1, voluntary and electrically induced contractions were recorded in 14 endurance-trained (ENDU) men (seven cyclists: age 25 ± 2 yr, mass 70 ± 8 kg, height 175 ± 5 cm; and seven triathletes: age 27 ± 4 yr, mass 71 ± 5 kg, height 179 ± 6 cm) and seven explosive power-trained men (EXPLO: age 24 ± 1 yr, mass 73 ± 5 kg, height 179 ± 4 cm). Maximal knee-extension torque, activation level (twitch interpolation technique), electromyographic activity of agonist and antagonist muscles, and twitch contractile properties were assessed. Results: At preexercise, the maximal voluntary isometric and concentric torques of EXPLO were greater than those of ENDU (P < 0.05). After the fatiguing exercise, significant isometric (18%; P < 0.01) and concentric (25%; P < 0.05) torque decreases in EXPLO were associated with, respectively, twitch torque (Pt) and maximal rate of twitch development (+dPt/dt) reductions (P < 0.01) and with an increase in the antagonist coactivation level (P < 0.01). No modification was observed for ENDU. Interestingly, the coactivation level was also increased (P < 0.01) in eccentric contraction for EXPLO, although the maximal eccentric torque decrease (P < 0.01) could not be specifically attributed to any group. Conclusion: The fatiguing exercise induced central and peripheral adaptations, but the mechanisms differed regarding the contraction mode. At pre- and postfatiguing exercise, it seems that the neuromuscular profile depends on the subject's training background and the contraction modes used to assess fatigue