Psychometric and Physiological Responses to a Preseason Competitive Camp in the Heat With a 6-Hour Time Difference in Elite Soccer Players

PURPOSE: To examine in elite soccer players after traveling across 6 time zones some psychometric and physiological responses to a competitive camp in the heat. METHODS: Data from 12 elite professional players (24.6 ± 5.3 y) were analyzed. They participated in an 8-d preseason summer training camp in Asia (heat index 34.9°C ± 2.4°C). Players' activity was collected during all training sessions and the friendly game using 15-Hz GPS. Perceived training/playing load was estimated using session rating of perceived exertion (RPE) and training/match duration. Psychometric measures of wellness were collected on awakening before, during, and after the camp using simple questionnaires. Heart-rate (HR) response to a submaximal 4-min run (12 km/h) and the ratio between velocity and force-load (accelerometer-derived measure, a marker of neuromuscular efficiency) response to four ~60-m runs (22-24 km/h) were collected before, at the end of, and after the camp. RESULTS: After a large increase, the RPE:m/min ratio decreased substantially throughout the camp. There were possible small increases in perceived fatigue and small decreases in subjective sleep quality on the 6th day. There were also likely moderate (~3%) decreases in HR response to the submaximal run, both at the end of and after the camp, which were contemporary to possible small (~8%) and most likely moderate (~19%) improvements in neuromuscular efficiency, respectively. CONCLUSIONS: Despite transient increases in fatigue and reduced subjective sleep quality by the end of the camp, these elite players showed clear signs of heat acclimatization that were associated with improved cardiovascular fitness and neuromuscular running efficiency.