A-42 Free Communication/Poster - Non-traditional Sports

Abstract

It has been proposed that III-IV muscle afferents (MA) from the working muscles are a major contributor to central fatigue (CF), i.e. exercise-induced reduction in voluntary activation (VA). However, in many studies, CF is not observed after high intensity dynamic exercise. This may be related to the relatively long time (∼2 min) between exhaustion on the exercising ergometer and the measurement of CF on the dynamometer. For this reason we developed a one leg dynamic exercise (OLDE) involving the knee extensors (active extension and passive flexion) on a dynamometer allowing a short delay (∼10 s) to assess i) the discharge of MA via post exercise muscle ischemia (PEMI, study 1) and ii) the extent of exercise-induced CF (study 2). PURPOSE: These studies aim to investigate the discharge of MA and extent of CF induced by OLDE to exhaustion. METHODS: Both studies consisted of 4 sessions performed on the right leg (1 familiarisation, 1 incremental test and 2 experimental time to exhaustion tests at 85% peak power). In study 1 (n=10), PEMI (300 mmHg) was performed on the exercising thigh and mean arterial pressure (MAP) was measured. In study 2 (n=8), VA, M-wave (M), cervicomedullary motor evoked potential (CMEP), motor evoked potential (MEP) and cortical silent period (CSP) were measured on the knee extensors. In both studies, measurements were performed pre and post exercise (at exhaustion or after 3 min). Two-way repeated ANOVAs were used for statistical analysis. Data are presented as change according to baseline ±SD. RESULTS: MAP during PEMI was higher at exhaustion (+18±17%, P<0.05) and recovered after 3 min (+7±11%). OLDE induced a decrease in VA (-11±10%, P<0.05) at exhaustion and after 3 min (-5±4%, P<0.05). CMEP/M area was lower at exhaustion (-39±11%, P<0.01) and recovered after 3 min (-6±17%). MEP/M area was higher at exhaustion (+28±27%, P<0.01) and after 3 min (+15±19%, P<0.01). CMEP/MEP area decreased at exhaustion (P<0.001) and recovered after 3 min. CSP was higher at exhaustion (+32±23%, P<0.01) and recovered after 3 min (+2±16%). CONCLUSION: These studies highlight the importance of minimising the time delay to assess exercise-induced CF. This is the first study to show increased intracortical inhibition and decreased spinal excitability associated with discharge of MA at exhaustion following dynamic contractions.