Exercise ending 30 min pre-dive has no effect on bubble formation in the rat.

INTRODUCTION: We have previously shown that exercise performed 20 h before a dive significantly reduces bubble formation in both rats and humans. Furthermore, exercise performed closer to the dive did not prevent bubble formation.

HYPOTHESIS: The present study was designed to determine whether exercise 30 min prior to a dive promotes bubble formation. The occurrence of many bubbles is linked to a higher risk of developing decompression sickness.

METHODS: A total of 58 Sprague-Dawley rats were randomly divided into a sedentary control group (n = 29) and an exercise group (n = 29). Rats in the exercise group ran on a treadmill for a total of 90 min at variable intensity up to 85-90% of VO2max. Then, 30 min after exercise, one rat from each group rested in a pressure chamber at 700 kPa (7 atm) breathing air, performing a simulated dive. Bottom time was 45 min; decompression rate was 50 kPa x min(-1) (0.5 atm x min(-1)). Immediately after surfacing (100 kPa, 1 atm), the rats were anesthetized and bubbles were measured discontinuously for the next 60 min.

RESULTS: There were no significant differences in survival (p = 0.55), median bubble grade (p = 0.67), survival time (p = 0.53), or the number of rats getting a bubble score > or = 2 (p = 0.79) between the groups.

CONCLUSION: The same type and intensity of exercise that reduces bubble formation when performed 20 h prior to a dive neither promotes nor reduces bubble formation if performed 30 min before a dive. The present data indicate that exercise completed 30 min before a dive does not increase the risk of developing decompression sickness in the rat.