Hot Weather Training and Performance

Summer is here and many of us have already noticed an increase in the number of days with hot and humid weather. And if you live or have lived in the Middle East you know that every day for the next four months IT WILL BE HOT!

Reviewing a little bit of physiology will give us a better understanding of how it can impact

our training


It has long been known that as humidity rises due to the environment’s lower evaporative capacity, thermoregulatory effort increases (Emax).

This decrease in Emax reduces heat dissipation from the skin surface to the environment, resulting in decreased sweating efficiency and increased wetted skin area.

As a result of the decrease in sweating efficiency, skin temperature would rise during exercise under humid conditions, causing an increase in skin blood flow and increased circulatory strain.

In addition to this, humidity and high temperatures can promote increased blood flow to the skin. This causes the heart to pump quicker and circulate twice as much blood per minute as it would on an average day.

Heat and sweating can also reduce the amount of fluid in the body, resulting in a reduction in blood volume and dehydration.

This might make it difficult for the body to cool down and put a strain on the heart.

Let’s delve a little deeper into the effects of heat stress and dehydration on exercise and performance.

Findings and studies

In a recent study (1) eleven unacclimatised well-trained male runners experienced significant thermoregulatory and circulatory strain during sustained steady-state running in a warm environment of 30C as Relative Humidity (RH) climbed to 61% and 71 %, respectively. When compared to the driest RH level of 23%, this was followed by a lower capacity to execute incremental activity to exhaustion within these two RH levels.

The current study found that the ability to control body temperature during running at 70% VO2max effort at 31°C ambient temperature deteriorated as RH increased, and became significantly and statistically affected when RH exceeds 60%.

An early research showed that by improving their evaporative heat loss capacity, individuals can regulate their core temperature during moderate intensity exercise, regardless of surrounding conditions, over a relatively large temperature range (5–30 C) defining the so called prescriptive zone to describe this set of environmental characteristics. This study though, did not consider the effects of rising RH, causing narrowing of the perspective zone. Within the previously mentioned RH levels (61% and 71%), this is reflected by a non-linear increase in core temperature as well as a higher level of skin temperature during the steady-state activity and the capacity to perform aerobic exercise diminishes progressively with a reduced core to skin temperature gradient.

Very interesting and practical findings have been highlighted in a study (2) which collected data on athletes participating in the Summer Olympics of Tokyo 2020. Exercise performance was severely affected among non-acclimatised elite athletes exercising in that hot and humid environment, as evidenced by a 26± 11% lower time to exhaustion.

Remember the first attempt of Sub 2:00 marathon by Eliud Kipchoche (3)? One of the things that scientists had to deal with was the “balance” between core temperature and outside temperature and humidity.

Another aspect that Sport Science has highlighted is the price that the athletes pays during fluid loss by sweating.

The following table , modified from Michael Lambert (4) of the Sport Institute of South Africa’s research, indicates the degree of heart rate increase after fluid loss and can be used as a reference for modifying heart rate during exercise.

Steps you need to beat the heat

Knowing how your body behaves in hot and humid conditions and being conscious of the effects of heat stress and dehydration on your cardiovascular system can help athletes to prevent and contain a bad race if not avoiding even catastrophic consequences.

First step is to accurately monitor your heart rate during exercise. If on one side Rate Of Perceived Exertion can be used to improve our body awareness, on the other hand knowing your heart rate zones / levels and monitoring significant changes, not only during the workout, but throughout the day will help you to keep dehydration at bay. Nowadays technology is available to monitor this important athlete parameter, from bracelets to chest straps Heart Monitors.

Second step is to slow down your intensity by monitoring your heart rate during the workout, and drink at least 8 to 12 ounces of fluids every 20 minutes (make sure you sip fluids to avoid gastrointestinal issues). Start drinking even before you begin your exercise session to help prevent dehydration. As you walk out the door, drink 6 to 8 ounces of fluids.

NOTE: The term “fluids” is used here loosely, because the content of what athletes should drink is another topic in itself, which will be addressed elsewhere and is beyond the scope of this article.

Third step is to get acclimatised, before any race performance. Adaptation starts with short exposures to heat and humidity, increasing in time. This is also valid for training. If the weather has changed and summer is already here, perform few short workouts in the heat before approaching the key ones.

Fourth step: plan your workouts strategically! There is no point in over-stressing the body and in particular the cardiovascular system by training in the heat for no specific reason. Choose the time of the day where environmental conditions are favourable, but also moments of the day when you are less tired.

You know already I am suggesting training first thing in the morning! Or keep it indoors!

By: Coach Tommaso


The effects of a systematic increase in relative humidity on thermoregulatory and circulatory responses during prolonged running exercise in the heat

Ahmad Munir Che Muhamed,aKerry Atkins,bStephen R. Stannard,cToby Mündel,c and Martin William Thompsond

Exercise Performance and Thermoregulatory Responses of Elite Athletes Exercising in the Heat: Outcomes of the Thermo Tokyo Study

Johannus Q. de Korte, Coen C. W. G. Bongers, Maria T. E. Hopman & Thijs M. H. Eijsvogels






Leave a Reply