No Performance Effects of Altered Carbohydrate Distribution During Intense Cycling

This study examined the effects of different carbohydrate ingestion patterns on endurance cycling performance and gastrointestinal comfort. It was hypothesized that increasing carbohydrate availability in alignment with decreasing endogenous stores would optimize performance while minimizing gastrointestinal discomfort.

Twelve trained male cyclists completed three randomized trials involving a 180-min intermittent cycling preload, a 15-min all-out performance test, and a maximal sprint to exhaustion. Participants ingested 90 g/hr of carbohydrates in an increasing (INC), decreasing (DEC), or constant (CON) pattern. Performance, substrate oxidation, rate of perceived exertion, and gastrointestinal comfort were assessed.

Carbohydrate distribution during exercise had no effect on 15-min all-out performance test (mean [95% confidence limits]: INC-CON -0.1% [-9.9, 11]; INC-DEC 5.9% [-8.6, 23]; DEC-CON -5.4 [-17, 7.8]) or time to exhaustion (INC-CON -0.6 [-3.8, 2.7]; INC-DEC 0.1 [-4.0, 4.4]; DEC-CON -0.7 [-4.0, 2.6]) performance. Carbohydrate oxidation was higher in DEC versus CON (7.1%; 2.7, 11.7) and versus INC (5.8%; -4.1, 15). Conversely, fat oxidation was lower in DEC versus CON (13%; -23, -1.8), while other contrasts were unclear. RPE was lower, but increased more over time in INC than CON. Nausea (standardized difference 1.2; 0.04, 2.3), stomach fullness (0.55; -0.15, 1.27), and abdominal cramping (0.84; -0.03, 1.7) increased over time in INC versus DEC.

Carbohydrate intake distribution had little clear effect on performance, though a decreasing pattern may support oxidation and gut comfort later in exercise. Even intake remains advisable, but uneven patterns may be acceptable when needed.