How Much Post-Dive Activity is Too Much?

A reader recently wrote our regular contributor Doc Vikingo to ask: “We all know that strenuous work after a dive is bad. My question is, how much is too much? Example: I make a shore dive in which I will swim out 200 yards and stay at 20 feet for two hours (shark’s teeth hunting). Surface swim back the 200 yards, then hump my gear back across the beach to the parking lot, about another 150 yards. Am I making myself more likely to suffer from decompression sickness? Is this situation something to worry about?”

Doc’s response: “Actually, we are no longer so convinced that all strenuous post-dive activity increases the risk of DCS. For example, a study in the June 2006 issue of Aviation, Space and Environment Medicine found that post-dive strenuous exercise after a single field dive to 100 feet reduces post-dive gas bubble formation in well-trained military divers. Additional findings are needed for normal sport divers.

“The main problem is we don’t yet know the level of strenuousness and the timing of post-dive exercise to suggest to the typical recreational diver. And acceptable levels of nitrogen loading at the time of strenuous post-dive activity are a related unknown. Pending the evidence necessary to better specify such parameters, humping gear back to the parking lot should be done with care. Rapid or powerful movements of joints or other skeletal and muscle surfaces are theoretically worrisome. Such actions may sow the seeds of DCS.

“If I may get scientific for a moment, by the processes of nucleation and cavitation, turbulence in fluids adjoining moving body surfaces results in the formation of miniscule entities named micronuclei. Given a sufficient inert gas loading, these may serve as receptacles for the diffusion of gasses passing from the dissolved to the free gas phase as the diver ascends. If micronuclei grow to bubbles of critical size and number, DCS may follow. So it is wise to handle heavy gear gently, perhaps by making several trips rather than just one, or even using a cart. The activity should not involve undue strain on the knees. The most knowledgeable DCS researcher I know has a near pathological fixation on knees as engines of micronuclei formation.

“Until further study, it is prudent for a diver to remain mildly active before and after a dive, and during ascent and the safety stop. Possibly the worst thing the diver can do is to become sedentary immediately after a dive, e.g., take a nap. Sedentariness reduces blood circulation and therefore off-gassing efficiency. As such, easy swimming between dives well might be beneficial.

“Divers in such places as the Galapagos may wish to take to land between dives. I can see no harm from leisurely walking or hiking, provided it does not involve steep inclines or declines that stress the knee and other leg joints. Gym workouts right after diving should be limited to light exercise. Heavy lifting and vigorous aerobics probably are best avoided. As a final caution, whatever type of exercise you chose, stay well hydrated.

“In conclusion, DAN’s advice on the timing of exercise during diving is, ‘Physical fitness - - including both strength and aerobic capacity - - is important for divers, both for physical safety and decompression safety. Regular exercise training is best scheduled to separate intense exercise and diving. Intense physical training should be done 24 hours on either side of diving activity. Any exercise within 24 hours of diving should involve the lowest possible joint forces.’ While I personally find the specified time parameter to be conservative, a diver is exceedingly unlikely to sustain exercise-related DCS issues if you follow this rule of thumb.”