The impact of making weight on physiological and cognitive processes in elite jockeys

Purpose: To examine the impact of making weight on aerobic work capacity and cognitive processes in a group of professional jockeys. Methods: Nine male jockeys and 9 age-, gender-, and BMI-matched controls were recruited to take part in two experimental trials, conducted 48 hr apart. The jockeys were asked to reduce their body mass by 4% in the 48 hr between trials, and controls maintained usual dietary and physical activity habits between trials. Aerobic work capacity was assessed by performance during an incremental cycle ergometer test. Motor response, decision making, executive function, and working memory were assessed using a computerized cognitive test battery. Results: The jockey group significantly reduced their body mass by 3.6 ± 0.9% (p < .01). Mean urine specific gravity (Usg) readings increased from 1.019 ± 0.004-1.028 ± 0.005 (p < .01) following this reduction in body mass. Peak work capacity was significantly reduced between trials in the jockey group (213 ± 27 vs. 186 ± 23 W, p < .01), although VO2peak (46.4 ± 3.7 vs. 47.2 ± 6.3 ml·kg·min^-1) remained unchanged. No changes were identified for any cognitive variable in the jockey group between trials. Conclusion: Simulation of race day preparation, by allocating a weight that is 4% below baseline body mass caused all jockeys to report for repeat testing in a dehydrated state, and a reduction in aerobic work capacity, both of which may impact on racing performance.