Carbohydrate loading failed to improve 100-km cycling performance in a placebo-controlled trial

We evaluated the effect of carbohydrate (CHO) loading on cycling performanc e that was designed to be similar to the demands of competitive road racing . Seven well-trained cyclists performed two 100-km time trials (TTs) on sep arate occasions, 3 days after either a CHO-loading (9 g CHO kg body mass-l day-l) or placebo-controlled moderate-CHO diet (6 g CHO kg body mass-l day( -1)). A CHO breakfast (2 g CHO/kg body mass) was consumed 2 h before each T T, and a CHO drink (1 g CHO kg.body mass-l-h-l) was consumed during the TTs to optimize CHO availability. The 100-km TT was interspersed with four 4-k m and five l-km sprints. CHO loading significantly increased muscle glycoge n concentrations (572 +/- 107 vs. 485 +/- 128 mmol/kg dry mt for CRO loadin g and placebo, respectively; P < 0.05). Total muscle glycogen utilization d id not differ between trials, nor did time to complete the TIS (147.5 +/- 1 0.0 and 149.1 +/- 11.0 min; P = 0.4) or the mean power output during the TT s (259 +/- 40 and 253 +/-: 40 W; P = 0.4). This placebo-controlled study sh ows that CHO loading did not improve performance of a 100-km cycling IT dur ing which CHO was consumed. By preventing any fall in blood glucose concent ration, CHO ingestion during exercise may offset any detrimental effects on performance of lower preexercise muscle and liver glycogen concentrations. Alternatively, part of the reported benefit of CHO loading on subsequent a thletic performance could have resulted from a placebo effect.