Physical Performance in the Cold – Helsingin urheilulääkäriasema

Competing, training, and operating in cold environments present unique physiological challenges that athletes, coaches, and military personnel must navigate to achieve peak performance. Tissue cooling during cold exposure can alter neuromuscular function, decrease movement economy, and activate cold-defence mechanisms that preserve core temperature. By understanding these effects and implementing effective strategies exposed individuals can support physical performance and mitigate cold-induced detriments and hazards.

Acute Effects of Cold Exposure

Humans strive to maintain a core temperature of approximately 37 °C. During cold stress, heat loss may surpass heat production, leading to a drop in body temperature. The extent of this change is determined by the heat balance equation, which consists of heat exchange with the environment (radiation, convection, conduction, and evaporation) and metabolic heat production (physical activity, shivering, and non-shivering thermogenesis).

With decreasing body temperature, the human body activates cold-defence mechanisms to increase heat production and minimize heat loss. Peripheral vasoconstriction is the body’s first line of defence, reducing blood flow to the extremities to preserve core temperature. As blood circulation to the arms and legs decreases, their temperature drops, narrowing the temperature gradient between the skin and the surrounding environment. This process effectively decreases heat loss and helps to maintain core temperature in cold conditions.¹ This is followed by the increase in heat production via shivering thermogenesis and non-shivering thermogenesis: the production of heat by involuntary muscle contractions and increasing metabolic activity. While shivering thermogenesis can increase metabolic rate up to fivefold, the increase in metabolic activity has a more modest effect.²

In addition to these involuntary cold-defence mechanisms, humans employ behavioural adjustments to generate heat. Individuals exposed to cold naturally increase physical activity, whether through exercise, fidgeting, or other spontaneous movement, to further boost metabolic heat production.¹ For reference, intense exercise can raise metabolic rate 15- to 20-fold, making it the most effective way to generate heat in cold environments.²

Physical Performance in the Cold

When heat loss exceeds heat production, the body begins to cool down, leading to physiological impairments in cardiovascular function, energy delivery, nerve conduction speed, skeletal muscle contraction, and perception of effort, ultimately reducing both aerobic and anaerobic performance, and limiting strength, endurance, as well as coordination in cold environments.³

Endurance Performance

Endurance performance is noticeably influenced by environmental temperature, when temperatures shift away from a commonly considered temperate environment (~20 °C) toward hot or cold extremes. While a moderate decline in environmental temperature can actually enhance endurance performance by preventing the excessive increase in core temperature, a more drastic drop in temperature hinders it as oxygen consumption at a given work rate increases and time to exhaustion decreases.^4,5

One contributing factor is the decline in movement economy when muscles are cooled. This increases submaximal oxygen consumption, placing greater metabolic demand and need for oxygen on the body, ultimately limiting endurance capacity.⁸ Maintaining heat with extra clothing poses its own challenges, as each additional kilogram of clothing increases energy cost by ~3 % and each additional layer by ~4 %.⁹ Finding the right balance between insulation and mobility is crucial for sustaining endurance performance in cold conditions. Laboratory research suggests that individuals wearing shorts and t-shirts can achieve optimal endurance performance at around 10 °C⁴, while those dressed in a light skiing suit with long-sleeved undergarments performed best at -4 °C.⁵ Thus it is clear that temperature alone does not dictate performance outcomes — clothing, exercise intensity, modality, and additional environmental factors such as wind speed, humidity, and precipitation all play a critical role in shaping physiological responses, thermal balance, and overall performance in cold conditions.

Endurance athletes should stay warm enough to maintain movement efficiency while preventing excessive increase in core temperature. Higher-intensity exercise generates more heat, allowing for lighter clothing, whereas lower-intensity efforts require additional insulation to maintain thermal balance. When temperatures are low, staying in warm indoor conditions and minimizing exposure before exercise helps prevent unnecessary muscle cooling, which would otherwise reduce efficiency and increase energy demands¹⁰. If avoiding exposure is not possible, external heating methods – such as insulative or heated clothing and warming packs – can be used to maintain muscle temperature before exercise begins. Additionally, a structured and extended warm-up period can play a crucial role in counteracting the negative effects of cold exposure and preparing the body for peak performance¹⁰.

Strength, Power, and Coordination

The effect of environmental temperature on muscle force and power production is well-documented: exposure to cool and cold environments lowers tissue temperature, leading to decreased muscle force output. Even a modest drop in muscle temperature – whether systemic or localized – can negatively impact strength and power.³ To compensate for the impaired mechanical and contractile properties of muscles, the body recruits more muscle fibers to perform the same amount of work, increasing energy expenditure and reducing efficiency. Efficiency is further reduced by the increased co-activation of agonist and antagonist muscle pairs, where both the recruited muscle and the one creating an opposing force will be activated. Cold muscle tissue is also characterized by a leftward shift in the force-velocity curve: less force can be produced at a given contraction velocity, thereby reducing power.³ Beyond strength and power, coordination and balance also decline in the cold, increasing both performance limitations and injury risk.³ To maximize performance and safety in strength and power sports, maintaining muscle heat through proper warm-ups, passive heating, and insulative clothing should be a key focus when competing in cool or cold conditions.

Cold temperatures decrease both endurance and strength performance as cold muscles produce less force and power, and movement economy is decreased increasing energy demands.

Increased air or water flow over the skin accelerates heat loss through convection. This effect can be due to environmental factors (e.g., increase in wind speed) or a change in movement speed (e.g., running or swimming faster). Wind-chill index can be used to estimate the combined effect of environmental temperature and wind, but this is significantly influenced by the individuals clothing choices (e.g., windproof garments).

Rainy weather can significantly increase heat loss even in moderately cool temperatures as the insulative properties of wet skin and clothes are decreased. Staying dry is crucial for maintaining heat. Moisture from sweating can also significantly influence the temperature of the skin.

Limiting cold exposure before exercise to prevent unnecessary muscle cooling can support performance. When warm indoor conditions are unavailable, wearing additional insulating layers and/or heat packs can help maintain muscle temperature and support heat balance before exercise begins and heat production is enhanced.

Insulative layers help reduce heat loss, but added layers and weight negatively impact movement efficiency and energy expenditure, especially for heavy protective equipment. The key is balancing enough, but not too much, insulation with mobility to optimize performance. Clothing plays a crucial role in thermoregulation during cold-weather exercise, particularly when fabrics become wet. To maintain warmth and performance, the following fabric qualities are recommended: efficient moisture wicking, fast drying rate, high moisture regain capacity, minimal insulation loss when wet.

Higher-intensity exercise generates more heat, reducing the need for excessive clothing. Lower-intensity activities require more insulation to maintain heat balance. Carrying heavy equipment can increase intensity and heat production even if moving at walking speeds.

The type of exercise can affect thermal balance by affecting factors of heat transfer. Sports where movement speed is high (e.g., cycling or skiing) have increased heat loss through convection. Heat loss is also increased when exercising in cold or cool water as water has ~25 times the thermal conductivity of air.

In cold conditions, a longer and more intense warm-up may be necessary to increase heat production and fully prepare the body for peak performance. Standard warm-up durations used in temperate environments may be insufficient, requiring adjustments to both duration and intensity to ensure proper physiological readiness.

Cold-Related Injuries

The decline in physical performance is not the only concern in cold environments – cold-related injuries, ranging from mild frostbite to life-threatening hypothermia, pose significant risks. Proper preparation is essential to manage these hazards and to ensure safety during cold exposure. With appropriate clothing, suitable equipment, and the right knowledge, cold exposure can be done safely. However, it is important to recognize that individual responses to cold vary, and even with identical clothing and gear, some individuals may be more susceptible to cold-related injuries than others⁷. Especially children and the elderly as well as those suffering from vascular dysfunctions may be susceptible to cold-related injuries.

Frostbite is the most common health hazard for athletes and soldiers during cold exposure, occurring when skin temperature drops below -0.5°C, causing tissue to freeze. Fingers, toes, nose, and ears are particularly vulnerable, as they are far from the body’s core and highly affected by cold-induced vasoconstriction, which reduces blood flow and heat supply. The primary causes of frostbite include inadequate clothing and equipment, as well as a lack of knowledge about cold exposure.⁶ An additional risk is contact cooling, which occurs when gripping highly conductive materials such as metal in cold environments, accelerating heat loss and increasing frostbite risk.⁷ Warming of the affected area should be done when the risk of refreezing is minimised, as refreezing can further contribute to the injury. Using warm water (~37 °C) is recommended for the rewarming process.⁶

Hypothermia is defined as the decrease in core temperature below 35,0 °C, and it can be categorized as mild (35—32 °C), moderate (32—28 °C) or severe (< 28 °C). Mild hypothermia is characterized by intensive shivering, social withdrawal, and other behavioural changes. During moderate hypothermia shivering decreases and finally stops entirely and the individual becomes confused or loses consciousness. A risk of arrythmias is present. Finally, when reaching severe hypothermia heart arrythmias and death become more likely.⁶ Early recognition and preparation are key to preventing hypothermia. If hypothermia occurs, mild cases can be managed by passive rewarming—allowing the body to generate heat through shivering in a warm, dry environment. More severe cases may require active heating strategies, but caution is necessary, as sudden movements can trigger arrhythmias, and rapid rewarming may worsen the situation in moderately and severely hypothermic individuals.⁶ While reaching hypothermia during intense exercise is unlikely in most situations, events with significantly increased heat loss, such as open-water swimming, pose a high risk for participants¹¹. The risk for hypothermia can be increased in land-based sports as well, especially when low temperatures are combined with rain, high movement or wind speeds, and prolonged exposure.

Cold Acclimation

The body’s adaptation to prolonged cold exposure is not entirely clear, but research has identified three distinct acclimation responses: habituation, metabolic adaptation, and insulative adaptation. Habituation is the most common response, where shivering and vasoconstriction responses become blunted after repeated cold exposure. This reduces discomfort and increases tolerance to cold, but it also allows for a faster drop in core temperature due to increased heat loss and reduced heat production. Metabolic adaptation involves an increased metabolic response, particularly through enhanced non-shivering thermogenesis (NST) to generate more heat. Insulative adaptation refers to an increased vasoconstrictive response, which further reduces blood flow to the extremities to minimize heat loss and better preserve core temperature. The type of acclimation response may depend on the extent of deep body heat loss and whether the cold stress is metabolically compensable – meaning if shivering and non-shivering thermogenesis can adequately defend core temperature. However, metabolic and insulative adaptations are generally small and may not play a major role in long-term survival and success in cold conditions.¹ A daily one-hour exposure to cold-water (14 C°) immersion for seven consecutive days has been shown to be enough to elicit reduced shivering and increased NST.¹² Research on cold acclimation’s effect on physical performance is limited, and there is no strong evidence to suggest that any form of cold acclimation significantly enhances physical performance in cold environments.

Most commonly observed acclimation response is habituation, where body’s cold-defence mechanisms (shivering, vasoconstriction) are blunted but thermal comfort and manual dexterity may be increased.

Both metabolic acclimation response, where heat production is increased through shivering and non-shivering thermogenesis, and insulative response, where heat preservation is increased, have been suggested by some researchers, but their effects on whole body thermal balance in the cold may be small. The type of acclimation response may depend on the extent of deep body heat loss and whether the cold stress is metabolically compensable – meaning if shivering and non-shivering thermogenesis can adequately defend core temperature.

Decreased vasoconstrictive response allows the body’s extremities to maintain a higher temperature increasing thermal comfort and manual dexterity. This in turn increases the thermal gradient and allows for greater heat loss during exposure.

A delayed shivering response to cold is commonly observed in individuals who are cold acclimated. This may increase comfort but reduces heat production.

Decrease in vasoconstriction and shivering may help the exposed individual feel more comfortable in the cold environment.

An insulative acclimation response has been suggested, where increased vasoconstriction with cold exposure decreases the thermal gradient between the skin and the surrounding air/water decreasing heat loss.

Increased non-shivering thermogenesis (NST) through brown adipose tissue has been suggested as an acclimation response to repeated cold exposure, but its’ effects may be negligible as under 1 % of human body mass and under 1 % of whole body heat production are accounted for by BAT. Other body tissues, such as muscle, may be largely responsible for the increased NST.

Cold environments present unique challenges for athletes, coaches, and military personnel, impacting physical performance, injury risk, and overall physiological function. Though cold acclimation may improve comfort and tolerance, its impact on performance remains unclear. However, with proper clothing, training, and knowledge individuals can minimize cold-related risks and maintain performance in extreme conditions. EP2 FINLAND brings the aid and assistance of field experts to your disposal. Utilizing these resources to guide you through cold exposure can increase your chance of success.

References:

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Authors:

Jere Borgenström, MSc;
Juha Peltonen, PhD, Adjunct Professor
Dominique Gagnon, PhD, Adjunct Professor