The Journal of Physiology published an article about the protective effect of exercise in the 24 hours prior to diving. It stated that researchers at the University of Split and St. Olaf's Hospital in Norway followed up on findings in rats with interesting studies on dry divers (chamber dives). With venous gas emboli they found a significant decrease in number and size of bubbles in divers after one bout of strenuous exercise in the 24-hour period prior to diving. The abstract can be seen at this link http://tinyurl.com/26jmp
NASA scientists have found that exercise tends to bring microbubbles out of saturation when a person is taken to altitude. See http://tinyurl.com/23ktk and related article at http://snipurl.com/r8z
NASA studies of bubble micronucleation show that basically, for the diver, strenuous exercise is adverse to diving about four hours before diving and 2 to 6 hours after diving. Other studies are variable; some showing that exercise while decompressing is helpful, others showing that arm exercise is helpful in off-gassing. Moving around is found to be better than sleeping and a hot shower or tub is thought to shunt blood away from the muscles and tendons, reducing the off-gassing process. See our revised web page at http://www.scuba-doc.com/exerdcs.html. In a recent article in 'Undercurrent', Doc Vikingo has written an article about exercise and bends that can be seen in full at this link: Exercise Before, During and After DivingIn the article, I note some information has been attributed to me - from my web page about exercise and DCS at http://www.scuba-doc.com/exerdcs.html. My remarks were based on the study " Effective lifetimes of tissue micronuclei generated by musculoskeletal stress" in Aviat. Space and Environ. Med., 68 (Suppl), A12. (1997); Dervay J, Powell M R, B D 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. "
We have received a letter from Dr. Alf Brubakk, one of the highly regarded authors of the study from Split/ NTNU in Trondheim providing us with more information about their studies and showing that the results actually supplement but do not disagree with the NASA findings. What they have shown is that exercise 24 hours before a dive reduces bubble formation both in rats and man, and also have shown that exercise 48, 10, 5 and 0.5 hours before the dive does not have this effect (Wisloff et al J Physiol 2004). Article at http://snipurl.com/54m9.
Dr. Brubakk also states that they have just finished a study where it is shown that exercise 0.5 hours before a dive increases bubble formation, which is in accordance with the NASA study. They also have a yet unpublished study where we have shown that the bubble reducing effect seems to require heavy (80-90% of max) exercise. So it seems that both timing and intensity of exercise is of importance.
Dr. Brubakk also has the following interesting remarks: "The really interesting thing is what is going on? We believe that this all has to do with the nuclei, the precursors to the bubbles. Heavy exercise make them initially grow, maybe even new ones are created, this effect lasts for about four hours. The exercise does however induce a biochemical process, which we believe is related to the production of NO (nitric oxide), which then changes the properties of the vessel wall, allowing the nuclei to be eliminated, new ones then need time to regenerate. We are presently testing if heavy exercise immediately before a dive will eliminate the bubble reducing effect of exercise 24 hours earlier."
Dr. Brubakk is on the cutting edge of research in this area and if the problem can be elucidated, I believe that he and his laboratory will be in the forefront. However, the diver is still placed in an awkward position - not knowing what to do about often necessary exercise getting to and from a dive site and even whether or not to consider the exercise from a previous dive. Appropriately timing exercise would seem almost impossible in the diver who does multiday diving and multidives per day.
So, where does this leave us in regards to the proper advice to give to the diver? No advice at all might seem to be better than erroneous advice until this is sorted out properly. However, it still makes sense for the diver not to engage in strenuous exercise either immediately before or after a dive - as available data seems to indicate that this can promote bubble formation.
Ernie Campbell, MD, FACS, Diving Medicine Online. http://scuba-doc.com/, email scubadoc@scuba-doc.com