By Alex Hutchinson, November 3, 2013
When University of British Columbia exercise physiology researcher
Luisa Giles noticed some tightness and wheeziness in her chest a few
years ago, she quickly zeroed in on a possible culprit.
avid cycle commuter and really, really embrace physical activity and its
importance,” she says. But she couldn’t help wondering whether her
daily rides, an hour each way along Vancouver’s busy streets, were doing
more harm than good. So she decided to look into it.
The results of her study, presented at the annual conference of the
Canadian Society for Exercise Physiology in Toronto last month, offer a
surprising twist in an ongoing debate. When it comes to mixing the
benefits of exercise with the health risks associated with breathing
polluted air, you may actually be better off when you’re pushing harder
and breathing more deeply.
No one doubts that clean air is better
than dirty air. Breathing particulate-laden air triggers a cascade of
inflammation and oxidative damage that spreads from the lungs throughout
You can track the daily rise and fall of air quality
readings by looking at the number of people admitted to hospital for
respiratory problems and other serious issues such as stroke and heart
On the surface, exercise takes that bad situation and
makes it worse, because you’ll be sucking in more bad air. But
trade-offs in the real world are often less clear: exercising in dirty
air versus not exercising at all; or commuting by bike versus sitting on
a bus travelling along the same traffic-clogged roads.
question that Giles and her adviser, Dr. Michael Koehle, at UBC’s
Environmental Physiology Lab tackled was the effect of prior exposure to
polluted air before exercising in clean air – a situation that might
occur if you respond to an air-quality alert by driving or busing to a
gym instead of exercising outdoors.
They found that pre-workout
exposure to polluted air raised heart rates during the workout by six or
seven beats, showing that the body was still struggling with
after-effects of the pollution.
Another important consideration is
the fact that exercise itself has powerful anti-inflammatory and
antioxidant properties that accumulate over time – something that
short-term experiments miss if they simply evaluate the effects of a
single bout of exercise in polluted air.
For example, in a study
published last year in Medicine & Science in Sports & Exercise,
Brazilian researchers exposed mice to diesel exhaust particles for five
weeks. Those that didn’t exercise showed high levels of lung
inflammation and oxidative stress, as expected. But those that exercised
five times a week in the diesel fumes were almost completely protected
from the negative effects.
Of course, not all exercise has the
same effects. In her latest study, Giles had 18 healthy volunteers cycle
in an environmental chamber for 30 minutes at a time, at either low or
high intensity, while breathing either clean air or air containing
levels of diesel exhaust you might experience when cycling along a busy
At the lower exercise intensity, diesel fumes increased the
amount of energy needed to maintain pace and forced the subjects to
breathe more heavily. The total volume of air inhaled per minute
increased from 39.9 litres in clean air to 44.5 litres with diesel
added. But at the higher exercise intensity, which corresponded to a
moderate but sustainable effort, there were no differences in
respiratory or metabolic response between the clean air and the dirty
Why would pollution cause problems during easy but not hard
exercise? The study isn’t able to answer this question, but Giles
suggests that different patterns of airflow within the lungs may play a
role. Heavier breathing may speed the diesel particulates past irritant
receptors in the central airways without triggering them.
findings may be particularly important for people with heart and lung
conditions that prevent them from exercising at higher intensities,
Giles notes. People with breathing problems also tend to be the most
sensitive to pollution, and should consider minimizing outdoor exercise
when air conditions are bad.
For healthy people, Giles’s research
adds to an increasingly complex picture that doesn’t lend itself to
absolute statements about when you should or shouldn’t exercise in
The best approach, she emphasizes, is to minimize
your exposure to pollution during workouts whenever possible. For
example, the air tends to be cleaner early in the morning than later in
the day, and on parallel side streets even just a block away from major
But if you find yourself biking down a busy street and
wondering whether you should stop, don’t panic. The best option of all,
it turns out, may be to pedal even harder.