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  Latest update: 9/22/2022

Temperature and riding at the extremes.

All our cells are powered by temperature dependent chemical reactions, and the enzymes that catalyze these reactions are temperature sensitive. These enzymes function optimally in a narrow temperature range around 98.6 degrees Fahrenheit. Lower the the temperature of a cell and these chemical reactions slow. Heat the cell above the optimum temperature for these enzyme dependent chemical reactions and the cell's metabolic machinery starts to fail.

The body's temperature reflects the balance between heat production (ATP formation and muscle cell contraction) and heat dissipation from sweating (evaporation) and radiation of heat from the blood flow to the skin. With normal activity, heat production is relatively stable and modification of heat loss is the major factor that changes to maintain a stable body temperature in the "normal" range of 98.6 degrees Fahrenheit.

High ambient temperature decreases heat radiation. Add humid conditions which decrease evaporative heat loss from sweating and the problem of dissipating heat from exercise is magnified. At the other extreme is the challenged to minimize heat loss. Wind effects will increase skin cooling and increase heat loss from radiation. And the return of colder blood to the core from the extremities will add to the challenge of core temperature at the physiologic optimum.

Is there an ideal temperature for aerobic sports? This study of marathon race results suggests an optimum ambient temperature of around 10 degrees or 50 degrees Fahrenheit for endurance events with a definite drop off at higher temperatures.

Numerous additional studies confirm that riding at temperature extremes impacts performance. This article documents the negative effects of both high and low ambient temperatures. To quote "The optimal aerobic endurance performance wearing a cross-country ski racing suit was found to be -4 and 1C, while performance was reduced under moderate warm (10 and 20C) and cold (-14 and -9C) ambient conditions." Since it is unlikely the temperature had an impact on equipment, this reflects a decrease in the power developed by athlete. If there was any question, this study provides the documentation of a decrease in performance at high ambient temperatures, which then improved when the body's core temperature was decreased with cold fluids.

And this cycling specific study "demonstrates .... a clear effect of temperature on exercise capacity....following an inverted U relationship."

The optimal environmental temperature for endurance exercise performance is almost certainly within the range of (10 - 17 degrees Centigrade / 50 - 63 degrees Fahrenheit)

Then there are equipment impacts to consider, especially in colder weather. This website shows the impact of low ambient temperature on both air resistance and the rolling resistance of your tires to slow times compared to a similar power output on a summer outing.

As the body is quite good at maintaining a stable "cell operating temperature" of 98.6 F it is unlikely that all these changes are due to the impact of temperature extremes on the cells' energy producing metabolic pathways. What other factors might lower power output in extreme temperatures?

Mitigation of Extreme Heat and Humidity

A number of techniques have been shown to be of benefit. In competition a number of studies have shown the benefit of precooling so the athlete starts the event at the lower end of their ideal core temperature.

For those of us doing recreational riding, drinking a cold beverage provides the easiest solution. delay a rise in core temperature. And it did increase time to exhaustion performance, but just shy of the level defined as "statistically significant". A second study supported the benefit of drinking cold beverages and again demonstrated an increase in performance (this time statistically significant) as did this third study documenting improved performance at high ambient temperatures when the body's core temperature was lowered with cold fluids. Bottom line? I add ice to my water bottle, and if I remember, actually put the bottle, partially filled, in the freezer the night before to form an internal "ice cube".

This article provides a nice summary of the various approaches to core cooling. It points out that cooling during an event is superior to pre event cooling in enhancing performance (original study) and provides a clear indication that maintaining an ideal core temperature has moved into the mainstream as another tool for professional athletes.

Training and competing in the heat.

I recently had a personal encounter with the effects of riding without adequate acclimatization to the heat. I train in the NW (Seattle) but was riding in the Sierras in California. On day 2 of a multi-day ride I had my first cramps (ever) while on the bike. Quad cramps that almost kept me from finishing. It was 95 degrees, we were climbing Emigrant Pass (8000 feet), my gloves were white with salt, and I'm sure I was not drinking enough. Fortunately they had electrolyte powder at the next rest stop, and I took 10 minutes to drink a couple of water bottles or rehydration fluid. And I slowed down. Lesson learned. As I read this recently published article, it definitely resonated. I'll quote a few pertinent sentences.

Indoor training.

Indoor training on rollers or a dedicated bicycle trainer present similar heat challenges. This article summarizes the concern as well as offering reasonable adaptations when it is the only training choice available.

Mitigation of Extreme Cold

Does riding in cold weather increase the odds of cycling injury? This blog suggests joint injury as a possibility. What does the literature have to say

Interestingly there is very little science which suggest that aside from frostbite from skin exposure (especially on the face and feet) and decreased performance in "cooled" muscles - the opposite of the warm up effect we have all experienced. Falling on an icy spot or from being distracted by the cold are reasonable possibilities, but are really indirect cold injuries.

For those of you that might be worried about long term harm, such as arthritis, there are no anecdotes or data. This suggests (to me) that long term physical issues resulting from winter riding are not an issue, and riding in the cold is no riskier physically than any other time of the year. And if you are in the group that experiences knee discomfort after riding, a pair of tights or knee warmers is an easy solution.

Proper clothing provides the best option, although there is still the overall impact of the general heat loss from breathing cold air as well as the breathability of most fabrics. Put on a windproof barrier and the challenge now becomes prevention of sweating and damp clothing that increases the clamminess with any slowing of pace and internal heat production.

All questions and suggestions are appreciated and will be answered.

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