Carbohydrate ingestion improves gross cycling efficiency and subsequent time-trial performance

Introduction:

Whilst many research studies monitor and report improvements in cycling efficiency (Coyle et al., 2005; Hopker et al., 2009), none state whether nutritional intake was controlled or recorded across the period of assessment. Also, improvements in gross efficiency potentially improve performance (Jeukendrup & Martin, 2001) yet little is known about the impact of carbohydrate ingestion on this. Therefore the aim of this study was to determine whether manipulation of carbohydrate intake would influence gross cycling efficiency and/or time trial performance.

Methods:

Six trained male cyclists (Age: 44 ± 5 years, Mass: 81.4 ± 2.3 kg, VO2max: 55.7 ± 8.3 ml.kg-1.min-1) completed two sets of two exercise tests at a steady-state submaximal exercise intensity (60% of Power at VO2max). In each set, participants were required to cycle for 2-hours and a day later, cycle for 1-hour followed by a 16.1km time-trial. These tests were repeated 1-week later. In a randomised cross-over design, participants consumed isocaloric diets (~4000kcal) that contained either a high (70%) or low (20%) proportion of carbohydrate in the 3-days preceding, and 24-h recovery period from, the first cycling tests. Additionally, participants were also provided with 300ml of either water (low) or a 6.4% carbohydrate solution (high) every 30mins during each test. During all submaximal tests, expired air was measured at 30 minute intervals in order to calculate gross efficiency (GE). Results: Mean GE across both days was significantly greater under high carbohydrate conditions (High Carbohydrate GE = 23.75 ± 1.86%; Low Carbohydrate GE = 22.64 ± 1.48%, p<0.001). Additionally, cyclists completed the performance time trial ~5% faster under high carbohydrate conditions (High Carbohydrate = 1490 ± 96secs; Low Carbohydrate = 1568 ± 128secs, p<0.05). Accordingly, when performance was corrected with workload as a covariate, ~49% of the variance in time trial time was explained by changes in performance efficiency. Discussion: Differences in gross efficiency were obtained following alteration of nutritional intake in the 3-days preceding, during and in recovery from, exercise. This suggests that careful control of nutritional intake is required to ensure the validity of gross efficiency measures. Also, the improvement in gross efficiency under high carbohydrate conditions enhanced time trial performance. This strengthens existing evidence that cyclists should increase carbohydrate availability to ensure optimal gross efficiency and performance