Exercising in the cold might reduce your body’s immune function, which could make you more susceptible to illness, according to research published in PLoS ONE. However, when research subjects went through a pre-exercise protocol that induced low-intensity shivering, their immune response was boosted after performing moderate intensity exercise.

Researchers found that when subjects exercised in "thermoneutral" conditions (22 degrees Celsius, or about 72 degrees Fahrenheit), their bodies had a strong response on a wide range of tests measuring immune and endocrine function. However, when they exercised in the cold (0 degrees Celsius, 32 degrees Fahrenheit), that response was suppressed.

The study did not look at how long after exercise these immune responses lasted, which would have a significant effect on the practical implications of the study’s findings. However, if you find yourself shivering out in the cold as you wait for your next mass-participation race to begin, think of the silver lining: it’s possible that you’ll be less likely to get sick high-fiving strangers along the route.

The study’s nine participants, all men, exercised on a treadmill at the two temperatures. They wore shorts and a t-shirt in both conditions.

Researchers took blood samples to measure participants’ immunological and endocrine changes while walking (50 percent of VO2 max) and running (70 percent of VO2 max, what most runners would consider to be a recovery run). To induce the proper level of low-intensity shivering, participants sat in the cold chamber for 40 minutes to two hours before working out.

Researchers believe that the increased norepinephrine response elicited by pre-exercise shivering is likely responsible for the boost to the immune system that they observed. Norepinephrine is a neurotransmitter released by the adrenal gland that contributes to the fight-or-flight response, helping the body brace itself for an attack. Researchers emphasized that they studied only the effects of low-intensity shivering, and that moderate- and high-intensity shivering would likely have different effects.

Lead author Dr. Dominique Gagnon said in an email to Runner’s World Newswire findings in her earlier work also bear notice. Her research has shown increased fat utilization when exercising in the cold; this should mean that it's easier to preserve your muscle glycogen stores, which are limited, when running long in the cold.

“Plainly said, sugar is your fast easy-go-to fuel during exercise but it is present in much lower quantity than fat," Gagnon wrote. "Therefore if you can enhance the use of fat as fuel, you are saving some of the sugar for later and can prevent early fatigue during exercise. In [an] ideal world, we would only use fat and consequently could run for weeks.”

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