Bright light and thermoregulatory responses to exercise.
The thermoregulatory responses to morning exercise after exposure to different schedules of bright light were examined. At 07:00 h, six males ran on two occasions in an environmental chamber (temperature = 31.4 +/- 1.0 degrees C, humidity = 66 +/- 6 %) for 40 min at 60 % of maximal oxygen uptake. Participants were exposed to bright light (10,000 lux) either between 22:00 - 23:00 h (BT (low)) or 06:00 - 07:00 h (BT (high)). Otherwise, participants remained in dim light (< 50 lux). It was hypothesized that BT (low) attenuates core temperature during morning exercise via the phase-delaying properties of evening bright light and by avoiding bright light in the morning. Evening bright light in BT (low) suppressed (p = 0.037) the increase in melatonin compared to dim light (1.1 +/- 11.4 vs. 15.2 +/- 19.7 pg x ml (-1)) and delayed (p = 0.034) the core temperature minimum by 1.46 +/- 1.24 h. Core temperature was 0.20 +/- 0.17 degrees C lower in BT (low) compared to BT (high) during the hour before exercise (p = 0.036), with evidence (p = 0.075) that this difference was maintained during exercise. Conversely, mean skin temperature was 1.0 +/- 1.7 degrees C higher during the first 10 min of exercise in BT (low) than in BT (high) (p = 0.030). There was evidence that the increase in perceived exertion was attenuated in BT (low) (p = 0.056). A chronobiologically-based light schedule can lower core temperature before and during morning exercise in hot conditions.
Atkinson
G
G
Research Institute for Sport and Exercise Sciences, Liverpool John Moores University, Liverpool, United Kingdom. G.atkinson@ljmu.ac.uk
Barr
D
D
Chester
N
N
Drust
B
B
Gregson
W
W
Reilly
T
T
Waterhouse
J
J
D000328:Adult; D001831:Body Temperature; D002909:Chronobiology Phenomena; D015444:Exercise; D005080:Exercise Test; D006801:Humans; D008029:Lighting; D008297:Male; D008550:Melatonin / Q000032:analysis; D005082:Physical Exertion / Q000502:physiology; D012463:Saliva / Q000737:chemistry
D008550:Melatonin