Reduced neuromuscular activity with carbohydrate ingestion during constant load cycling

The purpose of this study was to determine the effect of carbohydrate ingestion before and during intense constant load cycling to volitional fatigue on surface electromyographic (sEMG) activity from the vastus lateralis (VL) and vastus medialis (VM) muscles. After 24-h diet and training control, 8 well-trained subjects [maximal O2 uptake (VO2max) 66 ± 2 ml · kg-1 · min-1; mean ± SD] ingested 8 ml · kg-1 of either a 6.4% carbohydrate-electrolyte (CHO) or a placebo (PLA) solution immediately before, followed by 2 ml · kg-1 of the same solution every 15 min while cycling to exhaustion at 84 ± 1% of VO2max. Exercise time to fatigue was 13% longer with CHO ingestion compared to PLA (58:54 ± 8:48 vs. 51:18 ± 5:54 min:s, NS). VO2 (4.22 ± 0.11 vs. 4.20 ± 0.14 L · min-1), heart rate (172 ± 4 vs. 176 ± 4 beats · min-1), ratings of perceived effort (18 ± 0.1 vs. 19 ± 0.1), and rates of carbohydrate oxidation (314 ± 28 vs. 324 ± 26 ?mol · kg-1 · min-1) were similar for both PLA and CHO at exhaustion. There was no main treatment effect of CHO ingestion on blood glucose or lactate concentrations, nor plasma prolactin levels either during exercise or at fatigue. However, CHO ingestion attenuated the rise in EMG root mean square (RMS) activity during the latter stages (>45 min) of exercise and at the point of exhaustion for both VM (0.325 ± 0.010 vs. 0.403 ± 0.020 mV; p = .006) and VL (0.298 ± 0.011 vs. 0.370 ± 0.007 mV; p =.0004). We conclude that in well-trained subjects, the ingestion of carbohydrate attenuated the increase in surface electromyographic activity during intense, constant load cycling leading to exhaustion in ?1 h. The precise mechanism(s) underlying this effect cannot be attributed to alterations in CHO availability but, instead, may be linked to changes in afferent sensory input.