AbstractUnderwater sports such as artistic swimming and freediving, are characterized by periods of voluntary arrest of breathing, known as apnoea, while exercising. It is well known that apnoea leads to bradycardia and some other oxygen conserving responses, but little is known when exercise is conducted underwater, and the differences between exercise with intermittent and maximal apnoea periods. This review aims to understand and compare the physiological responses of the exercise performed underwater and the effect of the diving reflex in the heart rate, blood lactate, arterial pressure, arterial oxygen saturation and oxygen uptake, in different types of apnoea. A systematic review was conducted, searching studies in five scientific databases, according to specific criteria. 14 articles were selected for the analysis, using the method called PRISMA with systematic research, including just articles where trials were performed underwater. Artistic swimming and depth modalities of freediving are perceived as high intensity exercise. Blood lactate concentration (BLa), heart rate peak (HRpeak) and mean arterial pressure (MAP), depend more on exercise intensity, whereas arterial oxygen saturation (SaO2) and minimum heart rate (HRmin) is more related to apnoea duration. The diving response is more pronounced in freediving depth modalities due to impossibility of breathing. High intensity exercise mildly counteracts the diving reflex due to muscular and oxygen demands. Further investigation is needed in underwater sports, and physiological measurements should be performed according to a general consensus among researchers in order to avoid wide ranges of values in trial outcomes.

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