Gonzales, BR, Hagin, V, Guillot, R, Placet, V, and Groslambert, A. Effects of polyester jerseys on psycho-physiological responses during exercise in a hot and moist environment. J Strength Cond Res 25(12): 3432-3438, 2011-With the general acceptance that extreme environments have a detrimental effect on thermoregulation and human performance, the aim of this study was to investigate the influence of 3 polyester jerseys with knits of different sizes on physiological and perceptual responses in trained cyclists during exercise performed in a hot and moist environment. Ten trained male cyclists (mean ± SD, age: 29.1 ± 8 years, height: 177.12 ± 5 cm, body mass: 70.10 ± 6 kg), performed 3 tests of 15 minutes at 150 W on a calibrated home trainer by randomly wearing jerseys with small knits (SK), medium knits, and large knits (LK). While exercising, the jersey and torso skin temperatures, perceived exertion and hotness, and heart rate (HR) were continuously recorded. The major results of this study showed that perceived hotness with LK was significantly lower (p < 0.05) than with SK at minutes 10 (effect size [ES] = 1.18) and 12 (ES = 1.04) of exercise. The torso skin temperature with LK was significantly lower (p < 0.05) than with SK at minute 10 (ES = 0.84) and at minute 14 (ES = 0.81) of exercise, and the LK jersey temperature was significantly lower (p < 0.05) than with SK jerseys at minutes 12 (ES = 0.83) and 14 (ES = 0.90) of exercise. However, no significant difference was found in perceived exertion or HR. These results suggest that the use of polyester jerseys with larger knits could limit the drift of skin temperature and therefore increase the thermal comfort of cyclists during exercise performed in a hot and moist environment. Therefore, coaches are encouraged to take particular care that their athletes wear exercise-appropriate clothing in hot temperatures.