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 On the first morning of a two-day study, researchers had nine men in
their 50s and 60s do a series of exercise tests involving
semi-recumbent cycling, in rooms heated to 40 degrees Celsius (104
degrees Fahrenheit). After the exercise tests, researchers had the
men simulate a 7.5-hour workday in the heat. Finally, on the second
day, they had the men repeat the same exercises they had done the
day before, in the same hot, dry conditions.
During both series of exercise tests, the researchers measured the
men's whole-body heat loss, or their ability to cool off.
Compared to the first morning's exercise results, which were
obtained before the prolonged day of exertion in the heat, on the
second day men retained more body heat during intense exercise, and
they had more difficulty sweating.
Overall, men retained 31 percent more body heat on the second day of
tests, the study found.
"Our findings indicate that prolonged work in the heat compromises
thermoregulatory function and may elevate the risk of heat-injury on
the following day in older workers," lead study author Sean Notley
of the University of Ottawa said by email.
"Although the mechanism explaining this impairment is likely
multi-factorial, it is possible that fluid depletion on day one led
to reduced sweat secretion on the next day, indicating that
participants were not inclined to replace fluid losses occurring on
day one," Notley added. "This outcome reinforces the need for better
education on the importance of fluid replacement during work as well
as prior to and following work."
Performing back-to-back days of prolonged, arduous work in the heat
is common for workers in many industries including mining, utility
work, firefighting, and military service, researchers note in
Medicine and Science in Sports and Exercise.
In a previous version of the current experiment done with men in
their 20s, participants didn't suffer any reduced ability to sweat
and cool their body temperatures in cycling tests done the day after
the long day of exertion in the heat, researchers note.
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These results, combined with the results from the new experiment in
older men, suggest that middle-aged workers need to take extra
precautions to stay hydrated in the heat, Notley said.
Men in the current study typically got 30 to 60 minutes of aerobic
exercise three to four days a week. They were chosen because they
had similar physical characteristics, activity levels and aerobic
fitness levels to a group of career firefighters researchers
examined in a previous study.
During the simulated workday, the men wore coveralls and short
sleeve shirts and walked on treadmills set at a 2 percent incline
for two hours straight in three separate sessions. In between
sessions, they got breaks for food and water and were able to sit
down.
Beyond its small size, another drawback of the experiment is that
the treadmill sessions might not be a good proxy for the type of
exertion men might actually do on the job, the study authors note.
Still, the results underscore the need for men to take precautions
to avoid heat related injuries or heat stroke, which in severe cases
can leave people unconscious or in a coma.
"There is a need for fluid consumption guidelines during work as
well as prior to and following work and/or refinement to existing
work place heat exposure guidelines to consider the carry-over
effects of working in the heat," Notley said.
SOURCE: http://bit.ly/2GX3JrF Medicine and Science in Sports and
Exercise, online April 21, 2018.
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