while back, we looked at some research on whether or not running while you
have a mild illness, like a cold, has any detrimental effect on your
it turns out, the research says no: moderate exercise, like easy running,
has no impact on the duration or severity of symptoms from a mild
what about more significant illnesses?
you’re not going to get out and run normally when you’re laid up in bed
with a fever and an unruly stomach, but what about after you’re over the
worst of the flu?
you need to be more careful when returning to running, or can you you ramp
back up to full training right away?
to Running After Flu and Fever
isn’t much direct research into this topic—although intentionally
infecting willing volunteers with the common cold for the sake of research
can pass muster with a university’s scientific ethics board, using
influenza or another serious viral or bacterial infection treads into the
given that more significant infections can take abrupt turns for the worse,
it’s also not tenable to actively encourage people who’ve contracted
these infections naturally to exercise for a scientific study.
left is animal studies, along with observational papers and retrospective
studies on the few hard-headed individuals (most often young men) who
undertake vigorous exercise despite suffering from an infection.
of exercise after being sick
effects of exercise on the course of a significant viral or bacterial
infection are unclear. The only study I could find which directly addressed
this issue was a 2005 paper by three researchers at the
at Urbana-Champaign and The Ohio State University.
study looked at the impact of moderate exercise, prolonged exercise, or no
exercise on the course of an influenza virus infection in mice. The mice
were injected with influenza virus, then induced to exercise on a treadmill
either for 20-30 min per day or 2.5 hours per day for the next four days.
course of the viral infection was compared among the exercising mice and a
control group which did no exercise. The severity and lethality of the
influenza infection in the mice broadly mimicked the immune response seen in
human athletes in other studies.
moderately-exercising mice had improved survival rates and less severe
infections when compared to the control group, while the mice who did
prolonged exercise had a marginally lower survival rate and significantly
well-documented impact of infections is their ability to interfere with your
body’s internal heat management.
healthy athlete is astoundingly good at tolerating exercise even in
oppressive heat: by increasing perceived fatigue, the brain is able to limit
heat buildup in the body during a long session of exercise in hot weather,
which usually makes running or racing in the heat a very safe, though
perhaps unpleasant, proposition.
when you’ve recently had a significant viral or bacterial infection, your
risk for serious heat illness rises markedly.
2007 review of 994 cases of heat stroke hospitalization in the US Army
concluded that “prior infection is a risk factor for heat illness,” and
Tim Noakes cites other research which supports the same conclusion in his
2012 book, Waterlogged.
what should your plan be if you come down with a significant illness like
Göran Friman and Lars Wesslén of
authored a 2000 article which provided guidelines for exercise and illness
in sick athletes.
the case of a fever over 100° F, Friman and Wesslén recommend complete
rest until the fever subsides.
also recommend that athletes use caution in the first three days of an
illness (even when fever is absent), because even quite significant
infections can appear mild for the first day or two. Your takeaway – once
completely better, run easy and short for at least 3 days
and Wesslén also advise being cautious with exercise in the week following
a bacterial infection treated with antibiotics. Once your symptoms clear up,
you should be cleared to ease back into training, but don’t jump into hard
workouts or racing just yet. Your takeaway – wait at least a week before
resuming hard workouts after a fever or the flu.
in mind, a recent illness predisposes you to developing heat illness, and
fast running is by far the most significant causal factor for heat stroke in
cool weather isn’t a guarantee of safety—Dr. William Roberts, the
long-time medical director for the Twin Cities Marathon, reported a case of
heatstroke in a well-trained marathoner on a cool 50° F day in
runner had suffered a viral infection in the days leading up to the race but
decided to run anyways: the decision landed him in the hospital for five
days with a core body temperature of over 105° F.
make the same mistake as him!
not do a hard, continuous run, or race until you’ve been fully recovered
for at least a week from a significant viral or bacterial infection,
especially if it included a fever.