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 Lead author Ken Tokizawa and his research team at the National
Institute of Occupational Safety and Health in Kawasaki wanted to
examine the effect of sleep loss in work situations such as
construction sites.
“In the construction industry, falls are major safety problems,”
said Tokizawa in an email to Reuters Health. He added that heat
strokes may cause falls for workers.
Heat stroke itself is also a serious consideration, as it can result
in damage to the heart, brain, muscle and vital organs, said
Jonathan Moore, a lecturer in cardiovascular physiology at Bangor
University in Wales, in email to Reuters Health.
Tokizawa and colleagues recruited 14 men who were in good health and
had no sleep problems and studied them under four different
conditions: after a normal night of sleep with no nap, after a
normal night of sleep with a 30 minute nap after lunch, after
sleeping four hours in a night with no afternoon nap, and after four
hours of sleep, with the nap.
The lab test consisted of two 40-minute periods of walking in a
95-degree room, once in the morning and once in the afternoon. The
conditions were meant to simulate the construction and manufacturing
fields, so workers wore pants, jackets, boots and helmets during the
experiment.
The study team assessed the level of physical strain by measuring
participants’ rectal temperature, skin temperature and heart rate
throughout the experiment.
The participants also rated their own levels of sleepiness, mental
and physical fatigue, feelings of heat or cold, pleasantness and
thirst.
Lastly, the researchers measured the subjects’ reaction times.
They reported their findings in Occupational and Environmental
Medicine.
For the no-nap trials, people with restricted sleep had a higher
core temperature during the afternoon walking period. People with
less sleep also had higher skin temperature and sweating during the
afternoon.
The people with limited sleep also reported more sleepiness and
physical fatigue in the morning and afternoon and more unpleasant
feelings in the afternoon. They also had slower reaction times after
walking in the morning and in the beginning of the afternoon, though
this leveled out as the afternoon session went on.
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Taking a nap did not have an effect on core or skin temperature or
sweating for people with restricted sleep, but people who took naps
reported less sleepiness in the afternoon and felt less overheated
and fatigued.
People who had taken a nap also displayed faster reaction times at
the beginning of the afternoon session.
Moore noted in his email that napping seems to be beneficial for
vigilance, but it may increase the risk of heat injury.
Napping did not lower core body temperature and “participants
perceived themselves to be cooler than they really were during
exercise-heat stress,” Moore said.
He feels that this finding requires further investigation.
Tokizawa also said that while taking a nap while running on limited
sleep can recover some reduced alertness, it cannot protect against
heat stroke.
“Be careful about heat stroke when you have lack of sleep,
especially in the afternoon,” he advised.
SOURCE: http://bit.ly/1KFHMt7 Occupational and Environmental
Medicine, online April 23, 2015.
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