A
s a Toronto kid whose relatives on both
sides of the family hail from the prai-
ries, I often heard the familiar complaint
about eastern Canadian summers: “It’s not
the heat, it’s the humidity.” There’s some
truth to this for runners – but it’s not the
whole story. As the fall marathon season
approaches, you’ll be relieved to find that
changing weather conditions (accompanied,
of course, by improving fitness) will gradu-
ally make it easier for you to sustain your goal
marathon pace. Less heat and humidity play
a role, but there’s a third component that’s
often neglected: direct sunlight.
With concerns mounting over poten-
tially dangerous weather conditions for next
summer’s Olympic marathons in Tokyo,
researchers in Japan have been invest igat ing
which factors might play a role in over-
heating. At this year’s American College
of Sports Medicine (acsm) conference in
Orlando, scientists from Himeji Dokkyo
University and Hyogo University of Health
Sciences in Japan presented data on the role
of solar radiation – that is, the heat trans-
fer red f rom t he sun to your body in t he for m
of direct electromagnetic radiation, inde-
pendent of the air temperature.
They asked 10 volunteers to spend 45
minutes pedalling at a “somewhat hard ” pace
on a stationary bike outside. They repeated
this task three times, with an air temperature
of 31 C each time, but with varying degrees of
cloud cover: clear skies, with an average solar
power of 1,072 watts per square metre; thin
clouds, at 592 watts per square metre; and
thick clouds, at 306 watts per square metre.
Sure enough, even though the air tempera-
tures were identical, the cyclists felt hotter
and had higher skin temperatures when it was
sunnier, although their core temperatures
were unchanged. In the heat, they pedalled
more slowly and produced less power, with
the biggest differences found in the clear-
sky condition. That confirms previous results
from the same lab conducted with artificial
sun, which found that endurance time was
cut nearly in half when going from no sun
to full sun. The takeaway: yes, it’s the heat
and the humidity – and the sunlight. So be
grateful for the grey days of fall, and pray for a
cloudy marathon race day.Timing your iron
Keeping your iron levels high
is crucial for runners, since
iron plays a key role in ferrying
oxygen from your lungs to your
hard-working muscles. But even
if you k now you r levels a re low, it
can be challenging to raise them.
One reason is that exercise itself
triggers a long-lasting rise in a
hormone called hepcidin that
is linked to inflammation and
partially blocks iron absorption.
For runners logging lots of miles,
that means their best efforts to
choke down liver or iron supple-
ments might be going to waste.
Another presentation at the
acsm conference, this one from
an international team led by
researchers at the University of
Western Australia, tested two
different timing protocols. They
had 16 runners with low iron
levels go for a 90-minute run
either in the morning or after-
noon. Then, 30 minutes after
exercising, they had a stan-
dardized meal (either breakfast
or dinner) along with a liquid
iron supplement labelled with
special isotopes that allowed the
researchers to track its progress
through the volunteers’ bodies.
The results showed that
hepcidin levels were significantly
higher three hours after running,
and stayed high for another 12 .5
hours. But fortunately, there
was a window immediately after
exercise before hepcidin levels
started to rise, allowing the iron
to be absorbed. There was also a
circadian pattern: hepcidin levels
gradually rise throughout the day,
so the morning dosage resulted
in greater iron absorption than
the evening dosage. The bottom
line is that morning is better than
evening, and if you run in the
morning, take your iron supple-
ment soon after you finish.
Of course, not everyone
needs iron supplements. By
some estimates, about 15 to
35 per cent of female athletes
have low iron; it’s less common
among men, perhaps because
iron loss during menstruation
is a factor. And you shouldn’tThere goes the sun...
32 Canadian Running September & October 2019, Volume 12, Issue 6
Maxine^ GravinaThescienceofrunning
alex hutchinson rounds up the latest in endurance research