Cycling At The Extremes Of Temperature

For the athlete, actual muscle temperature (which can vary from our core temperature) plays a role in performance. Looking at Muscle Power Output vs. Muscle Temperature

• From 86°F (30°C) to about 102°F (39°C), power output steadily increases.
• Peak power output occurs around 102°F to 104°F (39–40°C).
• Beyond 104°F, power begins to plateau or slightly decline due to overheating.

At rest, extremity temperature is generally lower than core temperature which explains the rationale of "warming up" to bring the muscle temperature closer to 102F.

Our core temperature reflects the balance between heat production (from ATP formation as well as muscle cell contraction) and heat dissipation from sweating (evaporation) and radiation of heat from the skin. With normal activity, heat production is relatively stable and modification of heat loss is the major factor maintaining a stable body temperature.

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 challenge of minimizing heat loss in cold conditions. Wind (and the airflow from riding) increase skin cooling and heat loss from radiation.

Is there an ideal ambient (external) temperature for aerobic sports? This study of marathon race results suggests an optimum temperature of around 10 degrees C 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?

• For the cold, there is clear evidence that skin temperature (and presumably extremity muscles as well) are impacted. To quote: "During the time course mean skin temperature decreased significantly with reduced ambient temperatures ..." And as your body cools (in this example) it seems likely that there is an effect on the contractile performance of the muscles directly as well as the blood flow to provide oxygen and nutrients. The net effect is a significant impact on power out put as demonstrated in this study - which again noted the association of a decrease in power output with the decrease in skin temperature.

• More likely the temperature/power relationship is based on the protective response of the "internal governor. A central, anticipatory, subconscious change in performance to assure a normal core temperature. This study is about heat effects (but I think we can assume a similar process to protect core temperature takes place with excessive cold temperature). To quote: "This adaptation appears to form part of an anticipatory response which adjusts muscle recruitment and power output to reduce heat production, thereby ensuring that thermal homeostasis is maintained during exercise in the heat."

Mitigation of Extreme Heat and Humidity

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.

• Only training in the heat will do the trick. "Although regular exercise in temperate conditions elicits partial heat acclimatization, it cannot replace the benefits induced by consecutive days of training in the heat."

• It will take 1 to 2 weeks for maximum acclimatization. "Most adaptations (ie, decreases in heart rate, skin and rectal temperature, increases in sweat rate and work capacity) develop within the first week of heat acclimatization and more slowly in the subsequent 2 weeks...(even trained athletes) may require 6-10 days to achieve near complete cardiovascular and as much as 2 weeks to optimize aerobic performance (ie, cycling time trial) in hot ambient conditions."

• Hot and humid is more stressful than hot and arid. "Although scientific support for this practice is still lacking, it may potentially be beneficial for athletes to train in humid heat at the end of their acclimatization sessions to dry heat to further stress the cardiovascular and thermoregulatory systems."

• If you are going to a hot climate, it may be time to move the trainer into the sauna. "Athletes who do not have the possibility to travel to naturally hot ambient conditions (so-called 'acclimatization') can train in an artificially hot indoor environment (so-called 'acclimation')."

• And finally, hydration is essential. Even though I have, on other pages, quoted a few studies that suggest hydration is too highly stressed, if you are competing in hot temperatures, are not hydrated, and are not sweating, the effects of heat are multiplied. And you need to take salt (electrolytes) as well as plain water.
  • Before training and competition in the heat, athletes should drink 6 mL of fluid per kg of body mass every 2-3 h, in order to start exercise euhydrated.
  • Athletes training in the heat have higher daily sodium (ie, salt) requirements than the general population. Sodium supplementation might also be required during exercise.
  • For competitions lasting several days (i.e., cycling stage race, tennis/team sports tournament), simple monitoring techniques such as daily morning body mass and urine specific gravity can provide useful insights into the hydration state of the athlete.
  • Adequately rehydrating after exercise-heat stress by providing plenty of fluids with meals is essential. If aggressive and rapid replenishment is needed, then consuming fluids and electrolytes to offset 100-150% of body mass losses will allow for adequate rehydration.
  • Recovery hydration regimens should include sodium, carbohydrates and protein.

Core Temperature Sensors - a tool to optimize temperature training

These sensors provide a continuous and accurate measurement of core body temperature during training and racing. Traditional methods are often invasive (e.g., rectal thermometers, ingestible e-pills) and if not, only measure skin temperature which isn't a reliable indicator of core temperature.

While research on the specific use of core temperature sensors in biking is still evolving, here's a summary of the available data and potential benefits.

Modern sensors use a thermal energy transfer sensor placed on the skin (typically attached to a heart rate monitor strap or with adhesive patches) to estimate core temperature using algorithms which may also incorporate skin temperature and heart rate data. They typically connect via Bluetooth or ANT+ to cycling computers, smartwatches, and smartphone apps for real-time data display and recording.

Potential Benefits for Biking:

• Heat Training
  • Allows for safer and more effective heat acclimation by monitoring your core temperature in real-time and staying within specific heat training zones.
  • Heat training can lead to physiological adaptations such as increased blood plasma volume, improved VO2 max, and enhanced lactate threshold, potentially improving performance in both hot and cool conditions.
  • Helps athletes understand their individual heat response and tolerance.
• Avoiding Overheating
  • Provides awareness of when your core temperature is rising to a level that could negatively impact performance or lead to heat-related issues.
  • Allows athletes to assess the effectiveness of different cooling strategies during training to optimize race-day cooling plans.
  • Can help with pacing strategies and decisions about when to implement cooling techniques (e.g., ice vests, hydration).
• Optimizing Performance
  • Core temperature responses can vary significantly between individuals. Monitoring helps athletes understand their unique individual physiology in thermal regulation.
  • Helps understand the relationship between core temperature, effort level (power, heart rate), and performance.
  • May aid in determining optimal warm-up and cooling strategies.

Are core temperate systems accurate?

They do provide reproducible measurements during repeated tests. However, the validity (accuracy compared to a gold standard like rectal temperature) has been debated in some research. Some studies suggest potential overestimation at moderate temperatures and underestimation at higher temperatures compared to rectal measurements.

The accuracy of non-invasive sensors may be influenced by factors like sensor placement, skin temperature, and activity level. Ongoing research and algorithm improvements are likely to enhance the accuracy of these devices over time.

Core temperature sensors offer a novel way to monitor physiological response to exercise and environmental conditions in cycling. While the technology is still relatively new and ongoing research is important for confirming accuracy and optimal use cases, it holds promise for elite athletes looking to optimize their training, particularly for heat adaptation and performance in challenging conditions.

For those of us who are not committed to a rigorous training program, at the moment a significant investment with questionable benefit.

Indoor training.

Mitigation of Extreme Cold

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.