It’s important to understand what happens physiologically when ambient temperatures plummet further and further toward zero.
Runners experienced in dealing with harsh winters don’t need to be told the basics about how to protect themselves from the elements when the temperature drops to uncomfortable or potentially dangerous values. The Internet abounds with articles and blog posts emphasizing the need to dress in layers, protect exposed skin and so on. For competitive runners, the idea is to wear just enough to be safe and be able to do a hard workout or race when the mercury tells a daunting tale.
Less often addressed, however, is the “why” of performance impairment in extremely or even moderately cold conditions. Clearly, few, if any, world or national records have been set in sub-freezing temperatures, and it’s not just because few big races are held in the bitter cold. Virtually no runners report having set any personal bests in really chilly weather (unless that’s the only conditions they ever face) and practically everyone has noticed a performance drop in hard workouts even when feeling great throughout a session.
So what exactly goes on physiologically with athletes as ambient temperatures plummet further and further toward zero degrees Fahrenheit? For one thing, one of your fuel lines essentially becomes clogged.
“There are differences in fat metabolism in the cold, as blood is shunted centrally, blood flow to adipose tissue is decreased and less fat is mobilized,” says Matthew Laye, Ph.D., and winner of the 2014 USATF 100-Mile Trail Championship. “This might contribute to the marathon times being slower.”
Laye adds that metabolic, contractile and all other enzymes are most efficient at temperatures slightly warmer than what is seen in resting skeletal muscle in “normal” temperatures. In suboptimal conditions, athletes recruit more muscle to compensate for lower ATP and power generation, placing a greater burden on the body as a whole at a given speed.
Greg McMillan, an exercise physiologist and head coach of McMillan Running, adds a few factors that are less easy to quantitate.
“With the McMillan Elite group in Flagstaff, the athletes did suffer in the cold,” McMillan says. “They suggested that they just couldn’t get warmed up and that they experienced more ‘pounding’ from each workout.”
McMillan notes cold-weather issues such the challenge of where to send the increased blood flow with exercise—some of this blood must go to the working muscles for running, but in chilly environments this is competing for blood shunted to the body’s center to maintain core temperature. Echoing Laye, he says that muscle temperature is suboptimal and that runners’ connective tissues “just feel more tight and less bouncy,” and points out that winter’s harder roads only amplify the latter woe.
McMillan adds that extra clothing seems to play a role in slowing people down despite the presence of great cold-weather apparel options. Finally, some speed inhibition arises from psychological factors.
“The cold created an extra stress that usually wasn’t there on a day when they were trying to really focus on training hard,” says McMillan.
Also, ample published research on this topic exists.
— According to a 2012 article in the British Journal of Sports Medicine, a possibly disproportionate number of elite runners suffer from exercised-induced asthma, or EIA. In runners with diagnosed and undiagnosed EIA, the contributing factors to this condition include water and heat loss through the increased respiration during exercise, leading to the release of substances called inflammatory mediators. This in turn results in inflammation of the airways, impeding breathing. (Different studies have established that runners who don’t have EIA in normal weather are not susceptible to this cascade of events.)
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— In the 1990 book Training for Sports and Fitness, authors Brent Rushall and Frank Pyke note that in very cold conditions, athletes are continually trying to prevent heat loss and a fall in the core body temperature. The two ways to cope with this problem are to produce more heat or reduce the amount being lost. Exercise per se addresses the first concern, while constriction of the skin blood vessels—along with proper attire and taking care not to overdress lest your clothing become saturated with sweat, which draws heat away from the body—addresses the second.
— As you might expect, running in the cold while it happens to be raining slows you down even more, and not just because of the mental misery factor. In a 2013 article in the International Journal of Sports Medicine, a team of Japanese researchers concluded that, all else being equal, running in the rain results in lower temperatures not only in your skin but even your esophagus, and that you breathe harder, use more oxygen and generate more adrenaline and lactic acid at the same speed compared to “merely” cold conditions.
The upshot? Realistically, just as in the heat, you can take steps to reduce the misery factor while your body does its best to adjust to the environmental insult of extreme cold. But you’ll never be able to run quite as fast as you can when it’s mild to cool, so you should account for this when scheduling sessions in sub-freezing temperatures.