Laboratory Simulated Duathlon Performance: Effects of Pre-Exercise Meals

Aim: To determine the effects of a pre-exercise meal on simulated duathlon time-trial performance. Methods: Nine well trained male participants (age 28.6±5.9 yrs, body mass 77.4±8.2 kg, height 1.81±0.1 m, running VO2peak 4.8±0.5 l·min-1 and cycling VO2peak 4.3±0.6 l·min-1) performed simulated duathlon time trials following three pre-exercise dietary conditions. Participants fasted overnight and were randomly given isoenergetic meals of either high carbohydrate (HCHO) or high fat (HF) which contained 214.8g or 50g of carbohydrate respectively, or fasted (FAST) at breakfast 3.5h prior to exercise. Respiratory gas analysis took place at the start and end of each run and at the start, mid-point and end of the cycle stage to determine carbohydrate and fat oxidation rates. Venous blood samples were taken prior to and after each exercise modality to determine metabolite and hormonal responses. Results: Duathlon performance was not significantly affected by the meals ingested (101.9±6.7, 101.0±7.7, and 102.4±7.2 min for FAST, HCHO, and HF respectively). The meals caused alterations to substrate availability, resulting in higher carbohydrate and lower fat oxidation rates after HCHO (p<0.01), and this was mirrored by reduced levels of fat metabolites, glycerol (p=0.004) and NEFA (p<0.001). Conclusions: These data emphasize that the provision of carbohydrate before exercise has an effect of substrate oxidation and availability of fat metabolites but does not impinge on performance compared with a meal high in fat.