The inveterate runner or hiker on a dive trip often wants to know if there is any harm in exercising before or after diving. Of course, the problem is whether or not bubbles are induced by pre-dive exercise or by exercise immediately after a non-saturation dive.
The scientists at NASA are understandably interested in this aspect of decompression and have done studies to elucidate this problem with their extra-vehicular activity astronauts. To determine the answer to these questions, an elegant study was done by Dervay, J, MR Powell, and CE Fife, ” Effective lifetimes of tissue micronuclei generated by musculoskeletal stress” in Aviat. Space and Environ. Med., 68 (Suppl), A12. (1997); Dervay, J, MR Powell BD Butler, and CE Fife. From Doppler bubble determinations in this study the following can be deduced:
All strenuous activities for about four hours prior to scuba diving will increase micronuclei, thereby increasing venous gas emboli. Musculoskeletal activity will definitely increase the number of tissue micronuclei. That is an experimental fact. These micronuclei will persist for about two to five hours – again an experimental fact. There are no studies that show clearly what happens to these bubbles when they are compressed by a dive.
It is thought that if one were to put four restful hours between exercise and diving and six between diving and exercise, a diver should be in good shape in terms of absent bubbles. That is probably sufficient for non-decompression dives.
If one were to schedule their exercise activities in the morning and diving in the afternoon, there should not be a problem with this situation. One would not need to take off a whole day as far as exercise is concerned.
In regard to the hot shower or hot tub question post-dive, there is an increase in blood flow to the skin to eliminate body heat. When this happens, blood is shunted away from muscles (a ”steal”) and flows to the skin. We have increased perfusion to the skin but that is not of much help in prevention of DCS.
This is thought to be harmful to the diver attempting to off-gas due to the shunting of blood away from the musculoskeletal areas that need to have blood flow promoted. This is done by moderate, non-straining exercise, avoiding running, climbing ladders and lifting SCUBA tanks. However, non-strenuous movement is thought to be helpful – sleeping should be avoided..
There are mixed reports of exercise causing increased DCS in altitude exposed individuals (Pilmanis). On the contrary, there is evidence that exercising while decompressing is helpful in reducing decompression accidents. Muth et al, have found that exercise increases the elimination of nitrogen post-dives that are non-DCS producing. Jankowski has shown that exercise during decompression reduces the amount of venous gas emboli.