When is it better to exercise in the summer: in the morning or in the evening?

During the summer, it's best to exercise outdoors during the coolest part of the day—usually early morning or evening—rather than focusing on a fixed time like "before 10:00 a.m." or "after 6:00 p.m." The specific safe time depends on temperature, humidity, direct sun, wind, exercise intensity, and how accustomed you are to heat. The CDC recommends moving exercise to earlier or later hours and limiting intense activity during the middle of the day whenever possible. [1]

During extreme heat, early morning often proves advantageous. The World Health Organization advises avoiding strenuous physical activity during the hottest part of the day, and during heat waves, if intense activity is required, it cites the morning window of approximately 4:00 AM to 7:00 AM as an example. This isn't a universal training schedule for the entire summer, but rather an example of choosing the coolest period during extreme heat. [2]

Evening can also be suitable if the temperature has actually dropped. However, after a hot day, the air, pavement, and buildings can remain hot for several hours, so the rule "it's safe after 7:00 PM" is unreliable. It's more helpful to check the hourly forecast and choose the period with the lowest heat load.

If training takes place in a properly cooled room, summer heat is much less of a factor. Then, the time can be chosen primarily based on comfort, sleep, and individual performance: modern reviews do not confirm that everyone needs to train only in the morning or evening for health. [3]

Why does the same workout become harder in the summer?

Physical activity itself produces a large amount of heat. When the ambient temperature is high, the body must simultaneously eliminate both the metabolic heat of working muscles and the heat of the surrounding environment. To achieve this, blood flow to the skin and sweating increase. [4]

This creates competition between multiple tasks. Muscles require blood flow to function, skin requires heat dissipation, and continued sweating depletes the body's fluid levels. Heart rate can increase even at the same running speed or cycling effort, which was relatively easy to maintain in cool weather.

Cooling down becomes especially difficult in high humidity. Sweat cools the body not by appearing on the skin, but by evaporation. The more humid the air, the less evaporation occurs and the less heat can be released this way. Therefore, the CDC recommends considering not only temperature but also humidity. [5]

Direct sun adds radiant heat load. The WHO notes that temperatures are reported for shaded conditions, while in direct sun, heat exposure can be significantly higher. [6]

Therefore, jogging at 30°C in the morning in the shade and jogging at the same 30°C during the day on open asphalt are physiologically not the same workout.

Morning or evening: what's better in summer?

For safety in hot weather, temperature is more important than the position of the clock hands.

Early morning is often the coolest time of day. After the night, surfaces have had time to cool partially, and solar radiation is still low. Therefore, during intense heat, morning usually provides the most favorable conditions for running, brisk walking, cycling, and other long-distance activities. This is in line with WHO and CDC recommendations to choose cooler times of day. [7]

Evening is convenient because the sun's rays become weaker. Furthermore, it is often subjectively easier for a person to perform intense work in the afternoon: some measures of strength and athletic performance exhibit diurnal fluctuations and, for many people, reach higher values later in the day. [8]

But this benefit shouldn't outweigh thermal safety. If it's still 33-35°C (93-95°F) and high humidity in the evening, and it was 24°C (75°F) in the morning, a morning workout would be a more reasonable choice, even if the athlete typically feels stronger in the afternoon.

Conversely, in climates with cool evenings, training doesn't have to be moved to dawn just because it's summer.

Is there an ideal time to exercise for health?

There is no convincing evidence that one period of the day is universally beneficial for everyone.

A 2023 systematic review and meta-analysis examined strength and aerobic training programs conducted at different times of day. The authors found insufficient evidence that training at a specific hour consistently produced greater improvements in health or fitness. Some data showed an advantage when training times coincided with subsequent performance testing. [9]

Another meta-analysis found higher endurance performance in a number of tests in the afternoon or evening, but this relates primarily to athletic performance rather than evidence of greater health benefits of evening exercise.[10]

Therefore, in winter or in an air-conditioned room, one can consider one's chronotype, habits, and schedule. In summer, outdoors, minimizing heat stress becomes an additional priority.

Why you shouldn't rely solely on temperature

The reading of a conventional thermometer does not describe the entire heat load.

For example, 28°C with dry air, wind and cloud cover can be tolerated much more easily than 28°C with high humidity, full sun and no wind.

Complex indices are used to assess risk. One of the most informative for physical activity is the wet-bulb-black-ball temperature, or WBGT. This index takes into account air temperature, humidity, and radiant heat; in outdoor conditions, it also reflects the influence of solar radiation. NIOSH recommends the WBGT for a more accurate assessment of heat stress, although in everyday life, people often use the standard heat index. [11]

Sports organizations use WBGT not only to decide "go or don't go" but also to adjust training duration, number of breaks, equipment, and intensity. However, specific thresholds are not the same for all countries and athletes: they depend on climate, acclimatization, and the nature of the load. [12]

For the average person, the practical takeaway is simpler: before heading out for a tough workout, it's more useful to check the hourly temperature and humidity forecast than to automatically schedule your workout for the same summertime time.

Why Early Mornings Aren't Always Ideal

Morning usually wins in terms of temperature, but it also has its own characteristics.

Some people experience muscle stiffness immediately after waking, and their maximal power and strength may be lower than later in the day. Reviews of circadian changes in athletic performance do show a trend toward higher strength, speed, and power in the afternoon. [13]

This doesn't mean there's an increased risk of injury from morning training itself. However, before intense speed or strength training, a thorough warm-up is advisable, especially if you've just woken up and are used to working out in the evening.

Lack of sleep can also be a problem. Working out at 5:30 a.m. is unlikely to be a beneficial strategy if it means systematically cutting back on sleep at night. In this case, a later workout in cooler conditions or indoors might be more appropriate.

Therefore, "better in the morning" in summer means better in the cool morning with normal sleep, and not the need to get up before dawn at any cost.

Why is the evening sometimes worse than the morning even after sunset?

After sunset, solar radiation decreases sharply, but the temperature of the air and surrounding surfaces does not drop immediately.

Asphalt, stone, buildings, and other urban surfaces absorb heat throughout the day and then gradually release it. Therefore, the heat load may still be high in the early evening.

Humidity is also important. Sometimes the temperature drops in the evening, but the relative humidity rises, making sweat evaporation more difficult. As a result, the workout remains subjectively challenging.

This is why evening time should be chosen based on actual conditions, and not just on the absence of direct sun.

When to exercise during a heat wave

With a real heat wave, it's worth reconsidering your usual summer schedule.

The WHO recommends avoiding strenuous physical activity during the hottest hours of the day whenever possible. If intense activity is necessary, it should be postponed to the coolest part of the day; heatwave guidelines use early morning, approximately 4:00–7:00 a.m., as an example. [14]

In extreme temperatures, even early morning can be too hot. In such cases, a wise solution is to reduce intensity, shorten the duration, or temporarily move the activity to an air-conditioned room.

Missing an intense workout is far less dangerous than trying to maintain a training plan during extreme heat.

Why Heat Adaptation Matters

The body is capable of adapting to regular physical activity in a hot climate. This process is called heat acclimatization.

With repeated heat exposure, sweating becomes more efficient, circulatory stability improves, heart rate and core temperature decrease with the same amount of work, and skin blood flow adapts to the heat load. NIOSH recommends gradually increasing heat exposure over approximately 7-14 days. [15]

The CDC Yellow Book also indicates that most adaptations from regular exercise in the heat develop within about 10 days. Passive exposure to hot climates is not sufficient for full adaptation; physical activity in these conditions is necessary. [16]

Therefore, the first heat of summer is not the right time to try to immediately repeat the training volume of July last year.

If your temperature rises sharply, it's helpful to make your first workouts shorter and easier, gradually returning to your normal intensity.

Adaptation is lost faster than it seems

Thermal acclimatization does not last forever.

The CDC notes that after exposure to heat ceases, adaptation begins to wane over days and weeks. Therefore, an athlete who trained in a cool environment for a month or returned from a colder region may experience heat tolerance worse than expected. [17]

Physical fitness helps with overall exercise tolerance, but it doesn't completely replace acclimatization. A well-trained runner can still develop heat illness if the intensity is too great for the surrounding conditions. The American College of Sports Medicine expert consensus emphasizes that exertional heat stroke can develop even in trained athletes. [18]

This is especially important during the first days of a vacation in a hot country or during an unexpected heat wave.

Should I reduce the intensity in summer?

With severe fever - often yes.

If the body directs additional blood flow to the skin and maintains active sweating, the usual running speed or cycling power becomes physiologically more difficult.

Therefore, trying to maintain a winter pace at all costs in high temperatures increases heat stress. The CDC recommends starting physical activity more slowly on hot days and gradually increasing the pace. [19]

In practice, this might mean running slower, reducing the weight or number of sets, taking more breaks, choosing a shorter route, or replacing interval training with steady-state aerobic work.

This isn't a "bad workout." The strain on the cardiovascular and thermoregulatory systems is already higher in hot weather.

What workouts are especially demanding in hot weather?

The more intensely the muscles work, the more heat they produce.

Therefore, long runs, interval training, football matches, intense cycling and other prolonged activities create more heat stress than a leisurely walk or a short technical workout.

Clothing and equipment become an additional factor. NIOSH defines heat stress as the sum of metabolic heat, ambient temperature, and the effects of clothing or protective equipment. [20]

This is why the same air temperature may be quite tolerable for a leisurely walk, but unsuitable for intense interval running.

When is the best time to exercise indoors?

If outdoor conditions remain harsh both morning and evening, training in a cooler environment is often the safest option.

The CDC specifically recommends that in hot weather, consider an air-conditioned gym or other cool indoor space as an alternative to exercising outside.[21]

Indoors, you can continue to perform strength or aerobic training without exposing your body to additional extreme heat stress.

This is especially useful on days when you have an intense workout planned rather than a light recovery session.

How much should you drink during a summer workout?

There's no single hourly water requirement that's appropriate for every person. Your needs depend on temperature, humidity, intensity, duration of exercise, body weight, clothing, and individual sweat rate.

The CDC recommends paying extra attention to hydration on hot days and not starting a workout already dehydrated.[22]

However, during long-term exercise, there is also the opposite danger: excessive fluid intake. Wilderness Medical Society guidelines indicate that overdrinking is the leading preventable cause of exercise-induced hyponatremia, a dangerous decrease in blood sodium levels. For long-term endurance exercise, the most individualized strategy is to rely on thirst or a pre-assessed fluid requirement. [23]

So the goal is not to drink “as much as possible,” but to maintain adequate hydration.

Are electrolytes necessary?

For a normal short workout, a person who eats normally does not always need a special electrolyte drink.

During prolonged, intense exercise with heavy sweating, fluid and salt requirements become more individualized. However, adding salt does not protect against exercise-induced hyponatremia if a person continues to drink excessively. [24]

Therefore, the universal rule “in summer, any sport should only be done with electrolytes” is medically unfounded.

How to choose a training time in practice

Instead of the rule "only train at 7 a.m. in the summer," it's more useful to evaluate several parameters at once.

Conditions	A smarter choice
It's much cooler in the morning than in the evening.	Morning workout
In the evening the temperature dropped noticeably	Morning or evening, at your convenience
It's still very hot in the evening.	Morning is preferred
High humidity even at moderate temperatures	Reduce intensity or select a room
The intense heat continues around the clock	Cool room or light training
Heat wave	Avoid intense outdoor activity during hot hours
The man recently arrived in a hot climate.	Reduce duration and intensity during the first few days.
Intervals or long runs are planned	Choose the coolest window especially carefully

The main idea of the table is not to choose a specific hour, but that the intensity of the training should correspond to the thermal conditions.

Is it worth checking the heat index?

Yes, especially if the humidity is high.

The heat index combines temperature and humidity and therefore reflects subjective heat stress better than a conventional thermometer. The CDC uses this indicator to guide the public and advises particular attention to activity levels when the heat index is high. [25]

But the heat index is also not ideal for athletes because it does not fully take into account the intensity of the exercise itself, clothing, and solar radiation.

For organized sports, the WBGT is a more appropriate indicator. It combines several environmental factors and better reflects real-world thermal load. [26]

For casual training, it's enough to understand the principle: high humidity and direct sunlight make training more difficult, even if the temperature seems normal.

How to know when to stop training

Dizziness or severe weakness in the heat is already a reason to stop exercising and move to a cooler place. This is the CDC's advice to athletes and physically active people. [27]

Heat exhaustion can manifest itself as headache, nausea, dizziness, weakness, irritability, intense thirst, and profuse sweating. Continuing exercise while experiencing these symptoms is not recommended. [28]

Particularly dangerous are changes in the central nervous system—confusion, inappropriate behavior, severe loss of coordination, seizures, or loss of consciousness. In the context of intense exercise and high temperatures, this may be a sign of exertional heatstroke, which is a medical emergency. [29]

If heatstroke is suspected, seek emergency medical attention immediately and initiate aggressive cooling as quickly as possible. The ACSM expert consensus emphasizes that early recognition and rapid cooling are critical for survival. [30]

Who tolerates training worse in the heat?

Risk is determined not only by athletic form.

The WHO considers the elderly, pregnant women, and people with chronic cardiovascular, respiratory, renal, and certain other diseases to be more vulnerable to heat stress. Athletes and physically active people are also at increased risk due to the additional heat produced during exercise. [31]

Some medications can affect sweating, fluid balance, blood pressure, or the body's ability to tolerate heat. Therefore, if someone with a chronic condition or regular medication experiences unusual heat intolerance, it's wise to discuss exercise with a doctor.

Particular caution is required after a recent illness. Expert documents on heat illnesses include current or recent illness as factors that can impair exercise tolerance in the heat. [32]

Is it possible to exercise at midday if a person is accustomed to the heat?

You may be able to tolerate heat better after acclimatization, but adaptation does not make extreme conditions safe.

Thermal acclimatization reduces the physiological stress of a given task, but a person still produces metabolic heat and is dependent on the environment's ability to remove it.

Therefore, even well-trained athletes must adjust their exercise duration, intensity, and rest intervals based on thermal load. This is the basis for sports protocols using WBGT. [33]

Acclimatization expands the tolerable range of loads, but does not cancel the laws of thermoregulation.

Is it okay to exercise late at night?

Yes, if it doesn't interfere with sleep and the outside conditions have truly become more comfortable.

Systematic reviews do not suggest that evening exercise is generally detrimental to health. For some types of performance, performance is even higher in the evening. [34]

If a late-night intense workout impairs sleep for a particular person, it can be stopped earlier or the intensity reduced. However, the evidence doesn't support a universal rule like "exercise after 8:00 PM is harmful."

In summer, the choice between 07:00 and 21:00 is made more wisely based on a combination of temperature, sleep and individual tolerance.

What's more important: circadian rhythms or heat?

For recreational hot weather sports, environmental safety usually outweighs the potential small performance advantage of a particular time of day.

Research on circadian rhythms shows that some measures of strength, power, and endurance do vary throughout the day. However, a larger systematic review of training interventions found no convincing evidence that health or training progress is better for all people in the morning or evening. [35]

In other words, if an athlete shows their best results at 6:00 PM, but it is extremely hot at 6:00 PM in the summer, this is not an argument for training then.

Moving your workout to a cool morning is a much more physiologically significant decision.

What is often misunderstood

"In the summer, you shouldn't exercise after 10 a.m.." There's no universal time limit. In one area, dangerously hot temperatures may begin in the morning, while in another, it may remain moderately cool all day. You need to take actual conditions into account. [36]

"Evening is always safer than morning." No. After a very hot day, temperatures can remain high in the evening, while early morning is often the coolest time.

"If a person is well-trained, they are not at risk of heatstroke." It is. The ACSM expert consensus emphasizes that heatstroke during exertion can occur in apparently healthy athletes. [37]

"The more you drink, the safer it is to exercise." Dehydration increases thermal stress, but excessive drinking during prolonged exercise can lead to exercise-induced hyponatremia. [38]

"If you train in the heat every day, your body will completely adapt." Acclimatization does occur, but it only improves heat tolerance and does not eliminate the risk of extreme heat stress. [39]

Key points from experts

William O. Roberts, MD, MS, is Professor Emeritus in the Department of Family Medicine and Community Health at the University of Minnesota Medical School, a sports medicine specialist, and former president of the American College of Sports Medicine. His research interests include heat stroke, marathon medicine, and exercise-related diseases. [40]

Roberts is a member of the writing group for the current ACSM expert consensus statement on exertional heat illness. The group's position is that many heat illnesses can be prevented by recognizing and modifying risk factors, whereas heatstroke requires immediate cessation of exertion and rapid cooling. [41]

Susan Yergin, PhD, ATC, LAT, is an associate professor in the Department of Exercise Science at the University of South Carolina and an expert in thermoregulation, hydration, and exercise-induced heat illness. The university notes that she contributed to the development of heat acclimatization guidelines and updates to the ACSM and National Athletic Trainers' Association heat illness guidelines. [42]

Yergin is also a member of the ACSM expert consensus group. This document focuses on prevention not around a single acceptable temperature level, but rather around assessing risk factors, adapting the load to the environment, recognizing symptoms early, and being prepared for rapid cooling in the event of heatstroke. [43]

Frequently Asked Questions

What time is best to run in summer?

Typically, during the coolest morning or evening window. In extreme heat, early morning is often preferable because temperatures have not yet had time to rise. The CDC recommends moving activities to earlier or later hours. [44]

Is it possible to run at 30°C?

There is no single safe threshold. Risk depends on humidity, sun, wind, intensity, duration, acclimatization, and health status. Even at the same temperature, the stress on the body can vary significantly.

What's better in summer - training at 7 am or 8 pm?

Choose a period with less heat stress. If it's still hot in the evening, morning is preferable. If the evening is cool, both options may be acceptable.

Should you always slow down in summer?

Not always. If the conditions are comfortable, your usual intensity may be tolerated. If it's noticeably hot, the CDC recommends starting slower and increasing the intensity gradually. [45]

Is it possible to exercise in direct sunlight?

Yes, but the heat load will be higher than in the shade. In hot weather, it's best to choose shaded routes whenever possible and avoid intense exercise during periods of maximum sun exposure. [46]

When is the best time to do strength training in summer?

In an air-conditioned gym, the time of year is much less important. In this case, the time can be chosen based on convenience and individual performance. Research does not support a universal advantage of one time of day for training progress. [47]

Is it true that a person is stronger in the evening?

Many people do experience higher strength and power levels later in the day, but individual differences exist. This does not mean that evening training is always more beneficial or safer. [48]

How many days does it take to get used to the heat?

Major physiological changes usually develop within about the first week or two of regular exposure. NIOSH recommends gradual acclimatization over 7-14 days. [49]

Do I need to train in the heat specifically to get used to it?

Full thermal acclimatization requires physical activity in hot conditions; passive exposure to heat provides only partial adaptation. However, the activity should be increased gradually. [50]

What symptom means it's time to stop exercising?

Dizziness and pronounced weakness are already a reason to stop and move to a cool place. [51]

What are the dangers of confusion during exercise in the heat?

This could be a sign of heatstroke, a condition that requires immediate medical attention and rapid cooling. [52]

Is it better not to do any sports in the summer?

No. Physical activity remains beneficial year-round. The challenge isn't giving up exercise, but rather adapting the timing, intensity, and conditions of your workouts to the heat.

Conclusion

The best time for exercise in summer is not a specific hour, but rather the coolest and physiologically safest window of the day. For outdoor training, this is often early morning or cooler evening. During extreme heat, early morning is usually preferable; the WHO recommends avoiding intense activity during the hottest part of the day. [53]

When choosing a time, consider not only temperature but also humidity, direct sunlight, exercise intensity, and acclimatization. That's why 30°C alone isn't enough to determine whether running is safe.

If the heat remains high throughout the day, it's best to move intense exercise to a cooler room or reduce the intensity. If you experience weakness, dizziness, or symptoms of heat illness, discontinue the activity; confusion, seizures, or loss of consciousness require immediate medical attention. [54]