This study assessed fluid balance, sodium losses, and effort intensity during indoor tennis match play (17 ± 2 °C, 42% ± 9% relative humidity) over a mean match duration of 68.1 ± 12.8 min in 16 male tennis players. Ad libitum fluid intake was recorded throughout the match. Sweat loss from change in nude body mass; sweat electrolyte content from patches applied to the forearm, calf, and thigh, and back of each player; and electrolyte balance derived from sweat, urine, and daily food-intake analysis were measured. Effort intensity was assessed from on-court heart rate compared with data obtained during a maximal treadmill test. Sweat rate (M ± SD) was 1.1 ± 0.4 L/hr, and fluid-ingestion rate was 1.0 ± 0.6 L/hr (replacing 93% ± 47% of fluid lost), resulting in only a small mean loss in body mass of 0.15% ± 0.74%. Large interindividual variabilities in sweat rate (range 0.3–2.0 L/hr) and fluid intake (range 0.31–2.52 L/hr) were noted. Whole-body sweat sodium concentration was 38 ± 12 mmol/L, and total sodium losses during match play were 1.1 ± 0.4 g (range 0.5–1.8 g). Daily sodium intake was 2.8 ± 1.1 g. Indoor match play largely consisted of low-intensity exercise below ventilatory threshold (mean match heart rate was 138 ± 24 beats/min). This study shows that in moderate indoor temperature conditions players ingest sufficient fluid to replace sweat losses. However, the wide range in data obtained highlights the need for individualized fluid-replacement guidance.
Matthew J.E. Lott and Stuart D.R. Galloway
Stuart D.R. Galloway, Matthew J.E. Lott, and Lindsay C. Toulouse
The present study aimed to investigate the influence of timing of preexercise carbohydrate feeding (Part A) and carbohydrate concentration (Part B) on short-duration high-intensity exercise capacity. In Part A, 17 males, and in Part B 10 males, performed a peak power output (PPO) test, two familiarization trials at 90% of PPO, and 4 (for Part A) or 3 (for Part B) experimental trials involving exercise capacity tests at 90% PPO. In Part A, the 4 trials were conducted following ingestion of a 6.4% carbohydrate/electrolyte sports drink ingested 30 (C30) or 120 (C120) minutes before exercise, or a flavor-matched placebo administered either 30 (P30) or 120 (P120) minutes before exercise. In Part B, the 3 trials were performed 30 min after ingestion of 0%, 2% or 12% carbohydrate solutions. All trials were performed in a double-blind cross-over design following and overnight fast. Dietary intake and activity in the 2 days before trials was recorded and replicated on each visit. Glucose, lactate, heart rate, and mood/arousal were recorded at intervals during the trials. In Part A, C30 produced the greatest exercise capacity (mean ± SD; 9.0 ± 1.9 min, p < .01) compared with all other trials (7.7 ± 1.5 min P30, 8.0 ± 1.7 min P120, 7.9 ± 1.9 min C120). In Part B, exercise capacity (min) following ingestion of the 2% solution (9.2 ± 2.1) compared with 0% (8.2 ± 0.7) and 12% (8.0 ± 1.3) solutions approached significance (p = .09). This study provides new evidence to suggest that timing of carbohydrate intake is important in short duration high-intensity exercise tasks, but a concentration effect requires further exploration.