here’s no more vivid image of
the heat’s impact on running
performance than Scotsman
Callum Hawkins’ dramatic
collapse at the 2018
Commonwealth Games. Hawkins was
leading the marathon by two minutes,
with less than two miles to go, when
he collapsed with heat exhaustion.
On Australia’s Gold Coast, where
the race was held, temperatures had
tipped over 30C. That is not the norm
for UK runners, but with last summer
being the joint hottest on record and
the thermometer hitting 34C in June
this year, it’s not unusual for us to face
tough summer conditions.
In winter, we imagine running in the
summer sun as an idyllic affair; in
reality, every step can be a sweaty
effort; it leaves you fatigued, increases
your recovery time and affects the
intensity and volume of your next run.
A far from enjoyable experience and a
serious threat to your autumn PB.
Thankfully, there are measures you
can take to counteract the increased
effects of our local star. But first, you
need to understand what’s going on in
your body when things heat up. ‘It’s
really down to core temperature and
its impact on a variety of systems,’
says Professor Stephen Cheung,
head of the environmental
ergonomics laboratory at
Brock University,
Ontario, Canada.
When running in
the heat, our core
temperature will climb
from its optimal 37-38Cto 39-40C and possibly beyond, with
heat exhaustion likely between 40C
and 41C. ‘As a snapshot, this rise in
temperature alters brain chemistry
and impairs cognitive function,’ says
Cheung. ‘It also changes gut blood
flow, causing leakage into the system;
it increases free radical damage...it’s
not simply a case of core temperature
rises and you feel uncomfortable.’
The best way to combat these effects
is also the simplest: run more. As your
fitness grows, you experience a host
of adaptations that are conducive to
running better in the heat. These
include an improved sweat response
to dissipate heat quickly and greater
sensitivity of sweating response to a
rise in core temperature.
‘Improved aerobic capacity also
leads to elevated plasma volume and
cardiac output,’ says Cheung. ‘This
minimises the competition for blood
distribution between skeletal muscle
and skin.’ Racking up the miles helps
your body to develop both a greater
capacity for, and a slower rate of, heat
storage. But the latest science tells
us there are other ways to play it
cool besides just
putting the
miles in.T
ACCLIMATISING to the
heat is your best strategy.
This is where you train in
high temperatures to
stimulate heat-friendly
physiological adaptations.
‘The most significant is that
core body temperature
drops by around 0.3C,
resulting in less-impaired
performance,’ says
Cheung. ‘Acclimatisation
also decreases your skin
temperature, resulting in a
larger evaporative cooling
effect, and sweat rate rises
sharply, sooner – again for
cooling. Heart rate comes
in lower, too, which is
another sign of adaptation.’
Cheung has broken
acclimatisation down into:
short-term (fewer than
seven days exposed to the
hot environment); medium-
term (eight to 14 days); and
long-term (over 14 days).
If it’s not sun-lounger
weather, you can simulate
hot conditions to trigger
acclimatisation by wearing
extra layers, says Cheung.
‘It won’t be as effective at
raising core temperature,
but it will deliver partial
heat stimulus.’
Or you could take a
bath. ‘Research shows
that having a hot bath
straight after running in
“normal” temperatures
realises a small adaptation,’
says Cheung. The specifics
come from a study by
Neil Walsh of Bangor
University, Wales, which
found that moderate
exercise followed by a
15-minute bath in 40C
water over six days,
where bathing time rose
by five minutes each
day, resulted in a four
per cent improvement
in a 5K a time trial in
hot conditions. Walsh
reckons that the
improvement is likely to
be the result of ‘the joint
elevation of core body
temperature and skin
temperature’.FRIENDLY
FIRE
042 RUNNERSWORLD.COM/UK SEPTEMBER 2019