Solar Heating Effect on Human Body
High solar radiation has been recognised as a contributing factor to
exertional heat-related illness in individuals exercising outdoors
in the heat.
Although solar radiation intensity has been known to have similar
time-of-day variation as body temperature, the relationship between
fluctuations in solar radiation associated with diurnal change in
the angle of sunlight and thermoregulatory responses in individuals
exercising outdoors in a hot environment remains largely unknown.
The present study therefore investigated the time-of-day effects
of variations in solar radiation associated with changing solar
elevation angle on thermoregulatory responses during moderate-intensity
outdoor exercise in the heat of summer.
Eight healthy, high school baseball players, heat-acclimatised male
volunteers completed a 3-h outdoor baseball trainings under the
clear sky in the heat. The trainings were commenced at 0900 h in
AM trial and at 1600 h in PM trial each on a separate day.
Solar radiation and solar elevation angle during exercise continued
to increase in AM (672–1107 W/m2 and 44–69°) and decrease in PM
(717–0 W/m2 and 34–0°) and were higher on AM than on PM (both P < 0.001).
Although ambient temperature (AM 32–36°C, PM 36–30°C) and wet-bulb
globe temperature (AM 31–33°C, PM 34–27°C) also continued to increase
in AM and decrease in PM, there were no differences between trials in
these (both P > 0.05).
Tympanic temperature measured by an infrared tympanic thermometer
and mean skin temperature were higher in AM than PM at 120 and 180
min (P < 0.05). Skin temperature was higher in AM than PM at the
upper arm and thigh at 120 min (P < 0.05) and at the calf at 120
and 180 min (both P < 0.05).
Body heat gain from the sun was greater during exercise in AM
than PM (P < 0.0001), at 0–60 min in PM than AM (P < 0.0001) and
at 120–180 min in AM than PM (P < 0.0001).
Dry heat loss during exercise was greater at 0–60 min (P < 0.0001),
and lower at 60–120 min (P < 0.05) and 120–180 min (P < 0.0001) in
AM than PM.
Evaporative heat loss during exercise was greater in PM than AM
at 120–180 min (P < 0.0001). Total (dry + evaporation) heat loss
at the skin was greater during exercise in PM than AM (P < 0.0001),
at 0–60 min in AM than PM (P < 0.0001) and at 60–120 and 120–180
min in PM than AM (P < 0.05 and 0.0001).
Heart rate at 120–150 min was also higher in AM than PM (P < 0.05).
Neither perceived thermal sensation nor rating of perceived
exertion was different between trials (both P > 0.05).
The current study demonstrates a greater thermoregulatory strain
in the morning than in the afternoon resulting from a higher
body temperature and heart rate in relation to an increase in
environmental heat stress with rising solar radiation and solar
elevation angle during moderate-intensity outdoor exercise in
the heat.
This response is associated with a lesser net heat loss at the
skin and a greater body heat gain from the sun in the morning
compared with the afternoon.
...
...
...woah...
...i guess we combine that with our solar maximum knowledge...
...yes...
...then time we do...
...i'm in...!...
...ehhh...
...heyy...!...
Comments