**Jana AlQahtani, Deemah AlKhodairay, Mohammed AlHindi and Metab AlSulaimi**

## *8.1. Hot Environment and Physical Activity*

During exercise in hot weather conditions, if the air temperature exceeds 36 ◦C, the body gains heat by radiation and convection from the environment [1]. Subsequently, the blood flow through the skin and sweating increase, potentially leading to water and electrolyte imbalance, heat exhaustion, or heat stroke [2,3]. Symptoms of heat exhaustion include excessive sweating, feeling dizzy, increased heart rate, muscle cramps, nausea, and vomiting. Exercising outdoors is not recommended if temperature exceeds 39 ◦C (103 degrees Fahrenheit) because of risk of heat stroke. Thus, exercising indoors performed in air-conditioned facilities—e.g., in fitness centers is strongly recommended [4]. It relates particularly to individuals with cardiovascular disease.

Exercise training in hot temperature executed by sport professionals requires the implementation of adequate strategies—i.e., adequate fluid supplementation, suitable clothing, and heat acclimatization [5]. The necessary fluid replacement volume can be evaluated by body mass change—i.e., fluid intake should match sweat loss during exercise [6]. Adequate clothing—i.e., short-sleeve t-shirts, shorts, sport shoes, and head covers—is strongly recommended.

Heat acclimatization should comprise repeated exercise heat exposure over 1–2 weeks.

The first exercise sessions performed in the heat should be as short as 5–10 min, with at least a few hours of recovery between exercise bouts [7]. Heat acclimatization leads to improved sweating, improved skin blood flow, lowered body temperature, improved fluid balance, and altered metabolism [8,9]. The degree of adaptation is determined by the intensity, duration, frequency, and number of sessions of heat exposure, as well as the environmental conditions.
