The effect of short-term dietary manipulation on gross efficiency during cycling

To assess the effect of short term dietary manipulation on gross efficiency, 14 trained male cyclists (V̇O2max 56.6 ± 7.2ml.kg-1.min-1, mean ± SD) completed three 2-hour tests at a steady-state submaximal exercise intensity (60% of Power at V̇O2max). In the 3-days preceding each test, participants consumed a diet (~4000kcal.day-1) that was either high in carbohydrate (High CHO, [70% carbohydrate, 20% fat, 10% protein]), low in carbohydrate (Low CHO, [70% fat, 20% carbohydrate, 10% protein]) or contained a moderate amount of carbohydrate (Mod CHO, [45% carbohydrate, 45% fat, 10% protein) in a randomised, crossover designed study. Gross efficiency (GE) along with blood lactate and glucose were assessed at regular intervals (~30mins) and heart rate was measured continuously at 5 second intervals throughout the test. Mean GE was significantly greater following the High CHO diet than the Mod CHO diet. (High CHO=20.1% ± 0.5%, Mod CHO=19.3 ± 0.6%, mean ± SD; P<0.05). More specifically, GE was significantly greater after 25mins, 85mins and 115mins of the test (P<0.05). Dietary manipulation had no effect on blood glucose, blood lactate or heart rate responses during exercise (P>0.05). In conclusion, significant differences in gross efficiency were obtained following alteration of participants’ diet in the 3-days preceding assessment. This suggests that before the measurement of gross efficiency takes place, participants’ diet should be carefully controlled and monitored to ensure the validity of the results obtained.