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We sought to investigate the role of group III/IV muscle afferents in limiting endurance exercise performance, independently of their role in optimizing locomotor muscle O delivery. While breathing 100% O to assure a similar arterial O content (CO) in both trials, 8 male cyclists performed 5-km time trials under control conditions (H) and with lumbar intrathecal fentanyl (H) impairing neural feedback from the lower limbs. After each time trial, common femoral artery blood flow (FBF) was quantified (Doppler ultrasound) during constant-load cycling, performed at the average power of the preceding time-trial. The assessment of end-tidal gases, hemoglobin content and saturation, and FBF facilitated the calculation of leg O delivery. Locomotor muscle activation during cycling was estimated from vastus lateralis EMG. Using electrical femoral nerve stimulation, peripheral and central fatigue were quantified by pre/post-exercise decreases in quadriceps twitch torque (ΔQ) and voluntary activation (ΔVA), respectively. FBF (~16 ml.min.W; =0.6), CO (~24 mlO.dl; =0.9) and leg O delivery (~0.38 mlO.min.W; =0.9) were not different during H and H. Mean power output and time-to-completion were significantly improved by 9% (~310W vs ~288W) and 3% (~479s vs ~463s), respectively, during H compared to H. Quadriceps muscle activation was 9±7% higher during H compared to H (<0.05). ΔQ was significantly greater in H compared to H (54±8% vs 39±9%), while ΔVA was not different (~5%; =0.3) in both trials. These findings reveal that group III/IV muscle afferent feedback limits whole body endurance exercise performance and peripheral fatigue by restricting neural activation of locomotor muscle.
This article was published in the following journal.
Name: Journal of applied physiology (Bethesda, Md. : 1985)
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