Neuromuscular responses to mild-muscle damaging eccentric exercise in a low glycogen state

The aim of this study was to examine the effect of low muscle glycogen on the neuromuscular responses to maximal eccentric contractions. Fourteen healthy men (22 +/- 3 years) performed single-leg cycling (20 min at similar to 75% maximal oxygen uptake ((V) over dotO(2) max); eight 90 s sprints at a 1:1 work-to-rest ratio (5% decrements from 90% to 55% (V) over dotO(2) max until exhaustion) the evening before 100 eccentric (1.57 rad s(-1)) with reduced (RED) and normal glycogen (NORM). Neuromuscular responses were measured during and up to 48 h after with maximal voluntary and involuntary (twitch, 20 Hz and 50 Hz) isometric contractions. During eccentric contractions, peak torque decreased (RED: -16.1 +/- 2.5%; NORM: -6.2 +/- 5.1%) and EMG frequency increased according to muscle length. EMG activity decreased for RED only. After eccentric contractions, maximal isometric force was reduced up to 24 h for NORM (-13.5 +/- 5.8%) and 48 h for RED (-7.4 +/- 10.9%). Twelve hours after eccentric contractions, twitch force and the 20: 50 Hz ratio were decreased for RED but not for NORM. Immediate involuntary with prolonged voluntary force loss suggests that reduced glycogen is associated with increased susceptibility to mild muscle-damaging eccentric exercise with contributions of peripheral and central mechanisms to be different during recovery. (C) 2014 Elsevier Ltd. All rights reserved.