Physiologic and performance effects of sago supplementation before and during cycling in a warm-humid environment

The present study determined whether 0.8g/kg bodyweight sago ingested before (Pre-Sago) or during (Dur-Sago) exercise under warm-humid conditions (30 ± 2°C, 78 ± 3 % RH; 20 km·h^-1 frontal airflow) conferred a performance and/or physiological benefit compared to a control (Control) condition. Eight trained, male cyclists/triathletes (45 ± 4 y, VO₂peak: 65 ± 10 ml·kg^-1·min^-1, peak aerobic power: 397 ± 71 W) completed 3 15-min time-trials (∼75% VO₂peak) pre-loaded with 45 min of steady-state (∼55% VO₂peak) cycling following > 24 h standardization of training and diet. Measures of work completed, rectal and mean skin temperatures, heart rate, expiratory gases and venous blood samples were taken. Compared to Control, Pre-Sago resulted in a smaller rise in rectal temperature (0.3 ± 0.5°C) while heart rate increased to a greater extent (6 ± 13 beats·min^-1) during exercise (both P < 0.05), however, compared to Control time-trial performance remained unaffected (Pre-Sago: -0.5 ± 4.0%, P > 0.05). During exercise, plasma glucose concentrations were maintained higher for Dur-Sago than Control (P < 0.05), however substrate oxidation rates remained similar (P > 0.05). Dur-Sago also resulted in a higher plasma sodium concentration (2 ± 2 mmol·l¹) and lower whole-body sweat loss (544 ± 636 g) and, therefore, reduced plasma volume contraction (all P < 0.05). Heart rate increased to a greater extent (5 ± 13 beats·min^-1) during Dur-Sago, yet compared to Control time-trial performance remained unaffected (+0.9 ± 2.3%, P > 0.05). Uniquely, these results indicate that during exercise heat stress feeding sago can result in some 'beneficial' physiological responses, however these do not translate to changes in exercise performance when performed in a post-prandial state.