Fatigue Mechanisms During Repeated Exercise

Abstract

Little is known about fatigue mechanisms in a repeated exercise bout or the potential for protein in the restoration of exercise capacity. PURPOSE: To examine metabolic responses in the late stages of repeated exhaustive exercise when a carbohydrate-protein (CHO-P) supplement is ingested during short-term recovery. METHODS: Six runners (VO2max 64 ± 4 ml·kg-1·min-1) completed an initial treadmill run to exhaustion at 70% VO2max (Run-1) and repeated this 4 h later (Run-2). At 30 min intervals during recovery, a carbohydrate (CHO; 1.2 g sucrose·kg-1·h-1) or an isocaloric CHO-P solution (0.8 g sucrose·kg-1·h-1 and 0.4 g whey protein hydrolysate·kg-1·h-1) was ingested. Blood, muscle biopsy (analysis pending) and expired gas samples were taken at time-points necessary to explore the onset of fatigue. Data are mean ± SD unless otherwise stated. RESULTS: Run time to exhaustion with CHO and CHO-P was 81 ± 17 versus 84 ± 19 min in Run-1 (p=0.37) and 51 ± 13 versus 49 ± 15 min in Run-2 (p=0.43). The insulinemic response during recovery was higher in CHO-P than CHO (47 ± 18 versus 31 ± 7 nmol·240 min·l-1; p=0.05). Plasma glucose concentrations during Run-2 were similar in CHO and CHO-P and no differences were shown at the point of fatigue (CHO: 4.5 ± 0.8 and CHO-P: 4.4 ± 0.3 mmol·l-1; p=0.84). Plasma non-esterified fatty acid (NEFA) concentrations were also similar throughout Run-2 in both treatments with CHO (0.55 ± 0.25 mmol·l-1) and CHO-P (0.43 ± 0.26 mmol·l-1; p=0.29). Whole-body CHO oxidation was 3.1 ± 1.1 g·min-1 at fatigue with CHO; similar to CHO-P at the same absolute time-point (2.8 ± 0.9 g·min-1; p=0.34). Moreover, no differences were observed in fat oxidation between CHO (0.2 ± 0.3 g·min-1) and CHO-P (0.3 ± 0.4 g·min-1; p=0.36). CONCLUSION: Despite an increased insulinemic response with CHO-P ingestion during recovery, the restoration of exercise capacity and substrate utilization was similar between treatments. Thus, substituting a fraction of carbohydrate for protein in a recovery solution may be beneficial for other protein-mediated processes. Funder: Saudi Arabian Ministry of Higher Education.