Endurance exercise immediately before sea diving reduces bubble formation in scuba divers

Previous studies have observed that a single bout of exercise can reduce the formation of circulating bubbles on decompression but, according to different authors, several hours delay were considered necessary between the end of exercise and the beginning of the dive. The objective of this study was to evaluate the effect of a single bout of exercise taken immediately before a dive on bubble formation. 24 trained divers performed open-sea dives to 30 msw depth for 30 min followed by a 3 min stop at 3 msw, under two conditions: (1) a control dive without exercise before (No-Ex), (2) an experimental condition in which subjects performed an exercise before diving (Ex). In the Ex condition, divers began running on a treadmill for 45 min at a speed corresponding to their own ventilatory threshold 1 h before immersion. Body weight, total body fluid volume, core temperature, and volume of consumed water were measured. Circulating bubbles were graded according to the Spencer scale using a precordial Doppler every 30 min for 90 min after surfacing. A single sub-maximal exercise performed immediately before immersion significantly reduces bubble grades (p < 0.001). This reduction was correlated not only to sweat dehydration, but also to the volume of water drunk at the end of the exercise. Moderate dehydration seems to be beneficial at the start of the dive whereas restoring the hydration balance should be given priority during decompression. This suggests a biphasic effect of the hydration status on bubble formation.