GUIDE TO ESTIMATING WIND-CHILL TEMPERATURE
Assessing current and forecast weather conditions is the first step in managing cold injury risk. Aside from air temperature, there are several other factors that can influence wind-chill temperature, such as wind and rain. The Wind-Chill Temperature Index is a measure that accounts for air temperature and wind speed when gauging cold weather conditions. Figure 1 can be used to provide a quick and simple gauge of how to approach matches or training under given weather conditions. To use the graph:
- Read along the vertical axis to find the air temperature that accurately reflects the recorded air temperature
- Once air temperature is identified, read along to find the diagonal line that reflects the wind speed and if rain is present
- The shaded zone where the two lines cross reflects the recommended approach to playing under those conditions
Milder Wind-Chill temperatures require raising awareness of the possibility of cold injury and increasing vigilance of cold injury symptoms among players and coaches, while colder wind-chill temperatures may require players to increase the number of clothing layers to wear, or that events need to be modified to limit inactivity or exposure to cold weather. Consideration for cancelling events should be given when Wind-Chill Temperatures are severely cold. Further guidance on managing events under varying cold weather conditions is available later in the document (see ‘Implement Controls’).
For example, an air temperature of 1°C, light breeze, and no rain suggests that players should be made aware of the possibility of cold injury and be vigilant to symptoms of cold injury amongst each other. However, if it was raining, the same air temperature and wind speed may mean that matches need to be shortened and training sessions altered to reduce time spent stationary or inactive.
Based on the Wind-Chill Temperature Index, it is recommended that events be postponed, or suspended if ongoing, when air temperature falls below -15°C (5°F), regardless of wind speed or rain.
Figure 1. Wind-Chill Temperature Index Gauge
With rugby played in the winter months across varying climates, players will encounter diverse but generally tolerable weather. Severe cold weather is infrequent but can provide a source of discomfort, impair sporting performance, and predispose to cold injury if ill-prepared for. Despite these challenges, cold conditions should not be considered a barrier to playing rugby, which can be done safely if players and coaches are aware of the risks of cold injury and adopt suitable risk management controls.
Heat loss to the environment occurs when surrounding temperatures fall below body temperature, through radiation, evaporation, conduction, and convection. The greater the difference between surrounding temperature and body temperature, the greater possible heat loss from the body. Wet and windy conditions can increase the rate at which heat is lost.
The human body maintains an internal temperature between 37-38°C and regulates this narrow temperature range in several ways. When faced with a fall in core temperature, the body responds by shunting blood away from the extremities to minimise heat loss while generating heat by increasing physical activity. By reducing blood flow to the limbs, heat loss to the environment can be reduced by using muscle and fat tissue in the limbs to insulate the trunk region. Reduced blood flow begins with only a ~2-3°C drop in skin temperature at rest, but reaches a limit once skin temperature reaches 26-31°C. The main drawbacks of reducing blood flow to the limbs are:
- Increased risk of freezing injury to the hands and feet because of increased heat-loss
- Reduced dexterity in the hands and fingers
- Reduced effectiveness if exercising as muscles will still receive blood flow to support metabolism
While looking to reduce heat loss, the human body also responds to the cold by increasing heat production through remaining physically active. This increased heat production could either be done consciously through increasing physical activity or unconsciously through shivering, which involves repeated involuntary muscle contractions that begin in the torso and spread to the limbs. The degree and intensity of shivering relates to the extent of heat loss and can start immediately after the body is exposed to the cold. The main drawback of shivering is that its effectiveness can be blunted if the body is fatigued or short of fuel to continue work.
Individuals may acclimate if regularly exposed to cold weather over time, but the effects can be unpronounced, slow to develop, and thought to provide little practical benefit with balancing heat loss and production in cold conditions. Acclimatisation to cold weather is not thought to be useful in improving performance or preventing injury for these reasons, but may help with developing a tolerance to cold conditions.
Although individuals respond differently when exposed to the same conditions, cold injury sets in when heat loss to the surrounding environment overtakes internal heat production. Medical complications typically begin to occur when core body temperature falls below 35°C (95°F), with complications progressing as core temperature continues to decline. Being exposed to cold environments can cause medical complications either through cold-induced injury or worsening existing conditions.
The main cold injuries are broadly classified as hypothermia, direct freezing injuries, and non-direct freezing injuries, while medical conditions that can be worsened with exposure to cold weather include exercise-induced bronchospasm, cold urticaria, and cardiovascular disease. Hypothermia is defined as a core temperature that falls below 35°C (95°F), indicating a 2-3°C decrease from normal core temperature range. Because only a mild decrease in core temperature is required for hypothermia to set in, temperatures do not necessarily need to be freezing for individuals to become hypothermic. This has been supported by accounts of individuals suffering with hypothermia after competing in temperatures ranging between 10-24°C (50-76°F). Symptoms can vary from person-to-person at similar core temperatures, with early symptoms of Mild hypothermia (core temperature 32-35°C / 90-95°F) including shivering and behaviour changes such as apathy and social withdrawal. Moderate hypothermia (core temperature 28-32°C / 82-90°F) can involve confusion, slurred speech, sleepiness, while shivering will stop. Severe hypothermia (core temperature below 28°C / 82°F) affects heart rhythm and can render the individual unconscious.
Frostbite occurs when temperatures fall slightly below freezing point, commonly in exposed skin (nose, face, wrists) but also hands and feet if blood flow has been shunted away from the limbs. The first sign of frostbite is numbness in the affected area, usually when skin temperature falls below 10°C (50°F). As well as frostbite, chilblain is a more superficial freezing injury that can occur after just one-to-five hours’ exposure to cold and wet conditions at 16°C (60°F) and below. Chilblain is characterised by small red-coloured papules appearing on the skin surface with the fingers, ears, face and other exposed skin are commonly at risk, but there are no lasting effects from chilblain beyond some inflammation, and an itching or burning sensation once rewarmed.
Aside from directly causing injury, exposure to the cold can also trigger or worsen associated medical conditions. Among these, cold urticaria is an allergic disorder when the skin becomes itchy, red, and inflamed within minutes of exposure to the cold. This can lead to anaphylactic shock in some extreme circumstances. Exercising in the cold can also cause temporary narrowing of the airways, known as exercise-induced bronchoconstriction (EIB). EIB is thought to occur through a combination of inhaling cold, dry air as well as a reflex response to facial or skin cooling. Finally, exercising in the cold increases nervous activity, blood pressure, and demands on the heart when compared with exercising in warm conditions. As a result, individuals with underlying heart conditions may be at risk if playing sport or exercising in cold weather conditions.
RECOMMENDED STRATEGIES TO REDUCE SUSCEPTIBILITY TO COLD ILLNESS
Figure 2. Risk Management process as applied to cold stress (Adapted from Refs 1-2).
IDENTIFY / ASSESS HAZARD – HOW COLD IS IT?
Risk management (Figure 2) outlines a process starting with identifying possible hazards of exercising in cold conditions, assessing contributing factors to cold injury risk, and implementing appropriate control measures to reduce the risks. The first step in preventing cold injuries is to first assess how cold conditions will be when playing or training. For field sports such as rugby, a combination of cold air temperature, low solar radiation, wind, and rain provide the greatest risk of cold injury to players because these conditions increase the rate of heat loss. Relying on a single measure such as air temperature is unlikely to estimate cold injury risk accurately.
The Wind-Chill Temperature index combines wind speed and air temperature to reflect the air temperature felt on the exposed skin of a person walking at 3 mph in calm conditions (see figures 3a and 3b below). The shaded areas within both tables show the relative risk of frostbite and predicted time to reach freezing point (0°C / 32°F) for exposed facial skin. Windy conditions do not reduce the temperature of exposed skin beyond the surrounding air temperature but do increase the rate of cooling to meet surrounding air temperature. There are several other considerations needed when interpreting the Wind-Chill Temperature Index, such as the model not accounting for man-made wind that can occur when moving at speed such as when running, and wet skin will cool at a faster rate than dry skin if exposed to windy conditions. If wet skin is exposed to wind (through rain or sweating), the air temperature used for the table should be 10°C (50°F) lower than the actual recorded air temperature.
Based on the estimates provided from the Wind-Chill Temperature index, the risk of frostbite is less than 5% when surrounding air temperature is above -15°C (5°F). A Wind-Chill Temperature index falling below -27°C (-18°F) is enough for frostbite to set in to exposed skin in 30 minutes or less, coaches and players should be watchful for signs of frostbite and hypothermia when encountering wind chill temperatures in this range or lower. Once temperatures have fallen below this threshold, cancelling matches or training should be considered.
It is also important to note that local weather conditions can vary due to differences in landscape, with the presence of trees, buildings, and direction that the wind is blowing influencing exposure. Also important is to recognise that weather conditions may change during training and matches, so the risk management process should be continually evaluated in view of changing conditions and requirements to reduce cold weather exposure and cold injury susceptibility.
IDENTIFY / ASSESS CONTRIBUTING FACTORS
Once an assessment of cold weather hazards has taken place, the second risk management step includes identifying and assessing factors that may contribute to cold injury susceptibility. There are several factors related to the environment, sport and individual players that interact to determine if playing sport in the cold will increase physiological stress and injury risk beyond that experienced when playing sport in temperate weather. Heat loss is primarily determined by environmental conditions, while heat generation and retention are determined by sport, clothing, and player factors. Factors known to influence core body temperature are listed below:
The environment plays a key role in controlling cold injury risk, with cold, wet and windy conditions posing the greatest risk when playing field-based sports. Heat loss is much greater and faster in these conditions if not matched by appropriate clothing and exercise intensity. Windy conditions, both due to weather or “man-made”, can increase heat loss through convection, while exercising in the rain or wet clothes can also accelerate heat loss.
Being physically active can help to offset heat loss through increasing heat generation within the body, but only when the exercise is intense enough to balance against heat loss. Sports that involve frequent periods of physically intense whole-body activity, such as running, can be more effective at maintaining internal heat balance than just upper or lower body activity. Playing sport in wet and windy conditions dictates that exercise intensity should be greater to balance heat loss than in dry conditions. Muscle tissue can be a useful heat insulator at rest when in the cold, but exercising in the cold reduces this effectiveness because blood flow needs to be maintained to the exercising muscles. Exercising prior to being out in cold weather, or staying out in cold weather after training or matches have finished, may also increase the rate of heat loss.
PERSONAL (PLAYER) FACTORS
One of the most common reasons for cold injury is inappropriate clothing to match the weather conditions and physical activity. Clothing that does not retain heat or absorbs moisture can increase heat loss rates.
Body fat provides a useful purpose with insulating body heat, which is why people with a high body fat percentage tend to maintain core temperature better than lean people. Muscle tissue provides a similar purpose at rest, but this is reduced when exercising. There is also some suggestion that individuals with a larger body surface area, relative to body mass, tend to lose heat at a faster rate. Female athletes are thought to lose heat at a faster rate than male athletes because of the lower body mass (lower body heat content) relative to surface area (increased heat loss potential), but this may be offset a little by increased body fat in female individuals. Similarly, children also have a higher surface area relative to body mass, as well as lower body fat, than adults and so this can lead to increased heat loss when in the cold.
Physical fitness or training do not appear to directly help with balancing heat loss and generation in cold conditions, but fitter individuals can generate higher rates of body heat than less fit individuals by sustaining physical activity at a higher intensity for longer periods of time. Conversely, fatigue and underfeeding can impair heat generation by reducing the shivering response to the cold and the intensity and length of time that exercise can be performed for. Dehydration does not appear to be as limiting in cold conditions as it can be in hot conditions, although the cold can blunt thirst and excessive sweating without replacing lost fluid may reduce the ability to maintain intense exercise and maintain body heat balance.
The cardiovascular and nervous systems are important to maintaining heat balance within the body. Individuals that consume alcohol, drugs, or take medications that blunt the response of these systems to the cold may be at risk of cold injury.
Figure 3a. Wind chill temperature index in Fahrenheit
Figure 3b. Wind chill temperature index in Celsius
PLANNING AND EDUCATION
The first step in planning should be to perform a pre-participation screen of the players to identify individuals with a previous history of cold injury and those that may be susceptible to cold injury based on the risk factors identified above. Players that are identified as susceptible to cold injury should be monitored more intensely for signs or symptoms of cold injury. Along with the screening, players and coaches should also be educated about recognising and preventing cold injury, as well as the risks of playing sport in cold conditions. Players should be advised to:
- Report previous instances of cold illness to coaches or medics
- Remain well-hydrated and consume a balanced diet
- Bring changes of clothing for after training or matches
- Layer clothing as needed when playing, warming-up, cooling-down and at rest.
- Report early symptoms of cold injury (numbness or shivering) and be vigilant to these symptoms in other players (shivering, behaviour change)
Coaches, managers, and medical staff should:
- Check the weather conditions before and regularly during training sessions and matches
- Be aware of early signs of cold injury
- Implement a comprehensive pre-participation screening protocol that identifies high risk individuals for cold injury, as well as those with pre-existing medical conditions that can be worsened by cold weather
- Implement regular checks for signs of cold injury and provide plenty of opportunities for player to adjust layers of clothing as needed
- Allow some flexibility in team kit based on players’ individual heat balance needs
- Recognise the potential consequences and severity of cold injuries, such as hypothermia and frostbite
There may also be a need for game and training guidelines that can be referred to when managing cold, wet, and windy playing conditions. Guidelines should include using wind-chill temperature guidelines to make decisions about participation in given weather conditions, along with other considerations such as the length of the training session or match, and access to facilities and equipment for rewarming.
SCHEDULING TRAINING AND PLAYING
Training and matches should ideally be scheduled at times during the day when wind chill temperatures carry a low risk of cold injury (Wind-Chill Temperature Index above -18°C / 0°F). Using the Wind-Chill Temperature index, a guide to acceptable conditions would be:
- • Air temperature above -10°C (15°F)
- • Wind speed below 25 km/h (~15 mph)
Because players will respond to given conditions differently, this should not be taken as an absolute guide and players should still be watchful for signs of hypothermia and frostbite even though conditions are milder than those outlined above.
Historical weather reports can be used to gauge the expected weather conditions (air temperature, wind speed, likelihood of rain) at a given place and time. While useful for planning, those measurements may not necessarily have been recorded near the venue or at a similar time of day to planned training or matches and there may be some variation between the two locations and times. It is better to measure and record weather conditions as close as possible to the location and time that planned training sessions or matches will take place, both before and during training sessions and matches.
FACILITIES AND EQUIPMENT
The following supplies or facilities should be included either on the field, or at an accessible point near to where training or matches are taking place:
- Warm indoor environment
- Supply of water or sports drinks for rehydration as well as warm fluids for rewarming if required
- Heat packs, blankets, additional clothing, and external heaters (if feasible) for rewarming
Clothing represents the most effective protection against cold weather and injury by reducing heat loss to the environment through insulation and wearing multiple layers. Clothing layers provide the most flexibility to adjust insulation needs and prevent overheating, under-dressing, excessive sweating, and remaining dry. Typical clothing for cold weather includes the following:
- Base Layer: this layer is in direct contact with the skin and should wick moisture away from the skin surface to the outer layers where it can be evaporated
- Middle Layer: this layer should provide insulation
- Outer Layer: this layer should allow moisture to transfer to the air, while repelling wind and rain. This layer should not necessarily be worn when exercising unless it is windy or raining and should be worn when at rest
Clothing needs may change as exercise intensity and weather conditions change. As exercise intensity increases or weather becomes warmer, the amount of clothing and layers needed may
lessen. Given the number of factors that can influence cold injury susceptibility, enforcing a uniform clothing policy for an entire group can lead to some individuals overheating and sweating, while others may be unable to retain body warmth. It is important that individuals can change their clothing as the need arises. Commonly, players overdress when playing sport by wearing more layers.
Based on the Wind-Chill Temperature Index, the following considerations should apply if certain cold weather conditions are encountered (Ref 1):
If Wind-Chill Temperature Index indicates -1°C (30°F) and below:
- Be aware of the possibility of cold injury and communicate this to other team members (players, managers, parents)
- Regularly evaluate the weather conditions before and during matches for changes
- Try to arrange matches and training sessions at times of day when wind-chill temperatures are likely to be lowest (i.e. late morning / early afternoon)
- Water bottles may need to be contained within insulation material to prevent freezing.
- Players should have their inhalers nearby if required.
- Injured players should be removed from outdoor conditions if possible. If it is not possible, injured players should be insulated with blankets and/or multiple layers of clothing
If Wind-Chill Temperature Index indicates -4°C (25°F) and below:
- Ensure that players increase the number of layers they are wearing during the warm-up, cool-down, and when they are not playing
- In addition to clothing layers, hats and gloves may be used in training sessions to prevent heat loss and cold injury to the hands and head
- Ensure players have nearby access to warm and dry indoor facilities to rewarm. These facilities should also include access to dry blankets
If Wind-Chill Temperature Index indicates -9°C (15°F) and below:
- If playing multiple matches on the day, consider reducing the number of matches to be played.
- Consider shortening match or training session duration
- Try to minimise time spent stationary or at low intensity during training sessions
- Try to limit fatiguing activities to preserve energy levels during training sessions, particularly for female and young players
If Wind-Chill Temperature Index indicates -18°C (0°F) and below:
- Consideration should be given to cancelling outdoor matches and / or training sessions
To support regular checks of the weather during training and matches, a changing weather plan should be drawn up that can be referred to if cold weather worsens. Considerations within this plan should include:
- Including set periods where cold weather could be evaluated (e.g. half-time during matches, during breaks in training, etc.)
- Providing tips to coaches when evaluating the weather, such as simple examples to gauge wind speed (See figures 3a and 3b)
- Establishing set wind-chill temperature index thresholds where training and matches should be shortened or modified, or cancelled altogether
As well as the changing weather plan, standard operating procedures for implementing cold weather controls should also consider:
- Setting aside time during the pre- or early season where coaches, managers, and players can receive education about cold injury prevention and recognition
- Implementing a “buddy system” when cold weather is expected, where players are vigilant for cold injury symptoms among teammates
- Appointing a central contact for each team where queries about cold injuries can be directed (medical staff may be best placed for this role if available).
FROZEN PLAYING SURFACES
Frozen playing surfaces are a consequence of cold weather that should also be factored in when formulating and implementing controls. When frozen, playing surfaces may become harder than usual and the level of traction that players can achieve may also be affected, both of which may affect injury risk. Training or playing on partially thawed playing surfaces should also be approached with caution, as surface hardness or traction may be inconsistent as players move across the playing area.
Some of the cold weather controls outlined in this guideline can apply to frozen playing surfaces, such as undertaking periodic checks of the playing surface before and during training sessions and matches, scheduling training sessions and matches during the day when cold weather is least impactful and the playing surface has had time to adequately thaw, and ensuring players use appropriate footwear.
When checking the playing surface, pay attention to areas with limited access to direct sunlight (for example: areas shielded by buildings and trees), and which are covered by snow as these areas may take longer to thaw. Removing snow from the playing area will not automatically guarantee that the underlying playing surface is thawed.
There may be occasions where cold weather subsides or is lessened by implementing appropriate controls, but the playing surface is not adequately thawed. Coaches should use discretion when deciding whether to proceed with, abandon, or cancel training sessions in this circumstance. In the case of matches, the final determination of whether a match should be abandoned or postponed due to adverse weather conditions or the state of the playing surface lies with the referee, in conjunction with the recognised match-day doctor if present.
Cold weather should not necessarily be a barrier to playing sport, and often the risks can be minimised through prior education, planning, and responding to changing conditions. The considerations and recommendations within this guideline are intended as a framework of reference that unions, teams, and/or venues can use to operate safely when encountering severe cold weather conditions. Please note that it is beyond the scope of this guideline to make recommendations on treatment of cold injury or illness, which should be followed in accordance with each organisation’s respective care pathway.
It is important to note that this guideline is primarily for use while practicing or playing rugby when usual playing settings become cold and may not apply to situations where practicing or playing rugby in snow or deep cold is intentional, such as during snow rugby.
Cappaert, T. A., Stone, J. A., Castellani, J. W., Krause, B. A., Smith, D., & Stephens, B. A. (2008). National Athletic Trainers' Association position statement: environmental cold injuries. Journal of athletic training, 43(6), 640-658.
Castellani, J. W., Young, A. J., Ducharme, M. B., Giesbrecht, G. G., Glickman, E., & Sallis, R. E. (2006). American College of Sports Medicine position stand: prevention of cold injuries during exercise. Medicine and science in sports and exercise, 38(11), 2012.
Castellani, J. W., & Young, A. J. (2012). Health and performance challenges during sports training and competition in cold weather. Br J Sports Med, 46(11), 788-7