This study sought to determine whether afferent feedback associated with peripheral muscle fatigue inhibits central motor drive (CMD) and thereby limits endurance exercise performance. On two separate days, 8 males performed constant-load single-leg knee extensor exercise to exhaustion (85% of peak power) with each leg (Leg1 and Leg2). On another day, the performance test was repeated with one leg (Leg1) and consecutively (within 10-s) with the other/contralateral leg (Leg2-post). Exercise-induced quadriceps fatigue was assessed by reductions in potentiated quadriceps twitch-force from pre- to post-exercise (ΔQtw,pot) in response to supra-maximal magnetic femoral nerve stimulation. The output from spinal motoneurons, estimated from quadriceps electromyography (iEMG), was used to reflect changes in CMD. Rating-of-perceived-exertion (RPE) was recorded during exercise. Time to exhaustion (~9.3min) and exercise-induced ΔQtw,pot (~51%) were similar in Leg1 and Leg2 (P>0.5). In the consecutive leg trial, endurance performance of the first leg was similar to that observed during the initial trial (~9.3min, P=0.8); however, time to exhaustion of the consecutively exercising contralateral leg (Leg2-post) was shorter than the initial Leg2 trial (4.7±0.6min vs 9.2±0.4min, P<0.01). Additionally, ΔQtw,pot following Leg2-post was less than Leg2 (33±3% vs 52±3%, P<0.01). Although the slope of iEMG was similar during Leg2 and Leg2-post, end-exercise iEMG following Leg2-post was 26% lower compared to Leg2 (P<0.05). Despite a similar rate-of-rise, RPE was consistently ~28% higher throughout Leg2-post vs Leg2 (P<0.05). In conclusion, this study provides evidence that peripheral fatigue and associated afferent feedback limits the development of peripheral fatigue and compromises endurance exercise performance by inhibiting CMD.
- central motor drive
- neural feedback
- group III and IV afferents
- central fatigue
- Copyright © 2013, Journal of Applied Physiology