Do cool shirts make a difference? The effects of upper body garments on health, fluid balance and performance during exercise in the heat

Objectives Due to climate change and major sport events in hot climate, temperature regulation during exercise is gaining relevance in professional and amateur sports. This study compares the effects of an upper body garment with water-soaked inlays, of a synthetic- and of a cotton shirt on health, fluid balance and performance during a high intensity exercise session in the heat. Methods 32 healthy participants (age 25 ± 4 years; 15 women) were assigned to one of three upper body garments (cotton-shirt, synthetic-fiber-shirt, cooling-vest with water-soaked inlays) and underwent a high intensity steady state ergometer exercise test (Temperature 30.5 °C, frontal airflow 20 km/h, relative air-humidity 43 ± 13%). Time to exhaustion, physiologic parameters (inner ear temperature, heart rate, relative oxygen uptake, body weight, garment weight) and subjective data (perceived exertion, thermal sensation, skin wettedness, clothing humidity, feeling scale) were assessed. Time to exhaustion was analyzed using a survival time analysis. Other outcomes were evaluated using Kruskal-Wallis Tests and 95%-confidence-intervals. Results Time to exhaustion was not different between groups. Cooling-vests were heavier and led to lower inner ear temperature, lower thermal- and higher clothing-humidity-sensation at the start of exercise. Physiologic and subjective parameters showed no group differences at exercise termination. Conclusions In a realistic setting including frontal airflow, synthetic and cotton-fiber shirts reach comparable effects on health and thermoregulation and are perceived as equally comfortable. Although inducing a small pre-exercise cooling effect, a water-soaked garment induces a weight penalty and creates a less comfortable situation.