Timing of Exercise and Diving
After accepting the need for regular exercise to maintain physical fitness, the next issue concerns the timing of exercise training and diving. Scheduling outside physical fitness activities can be problematic when an active diving schedule is maintained. While part of this is simply a time management problem, there are other considerations. Conducting intense physical exercise too close to diving activity can be problematic for more fundamental reasons.
Bubble formation, while noted earlier as not equivalent to or a guarantee of DCS, can indicate an increased risk for it. Intense physical activity -- generally with substantial muscular forces and joint loading (the application of forces on joints) -- is believed to transiently increase micronuclei activity, the presumed agent of bubble formation. Intense physical activity too close to diving may therefore be problematic. Physical activity after diving may also stimulate additional bubble formation, possibly through a combination of increased micronuclei activity and increased joint forces. Interestingly, some preliminary work has shown that an intense bout of exercise conducted 24 hours prior to diving may reduce bubble presence in humans,3 possibly by inhibiting micronuclei activity. This potentially protective effect was not seen with exercise conducted closer to dive time. While this effect needs to be validated, the preliminary findings may support a simple rule of thumb for scheduling exercise. To reduce the risk, it is a good idea to avoid intense exercise 24 hours before and after diving.
The near-dive window will be best for low-intensity activities. Those who participate in cross-training activities may find it easiest to accommodate this schedule. For those who are more single-minded, diving may fit well into training rest days for those who put the priority on exercise, while training may fit best into diving rest days for those who put the priority on diving. Overall, lower training intensities will likely be more appropriate for the latter group, but accommodations can be reached.Timing of Exercise During Diving
Physical activity during the dive also has a direct impact on decompression safety.4,5,6,9 Exercise during the compression and bottom phase increases inert gas uptake, effectively increasing the subsequent decompression obligation of any exposure. It is important to remember that dive tables and computers estimate inert gas uptake, they never know reality. On the flip side, light exercise during the decompression phase (including safety or decompression stops) increases inert gas elimination and reduces risk. The caveat on exercise during decompression is that more is not always better. Too much or too intense exercise during the decompression phase can stimulate bubble formation, thus inhibiting inert gas elimination and increasing decompression risk.
We do not yet have sufficient data to quantify the difference between beneficial and potentially harmful exercise. Understanding the various issues and applying common sense confers the best protection. Most important is that moderate time-depth profiles are your best defense. Exercise considerations provide only a secondary defense. In terms of the secondary defense, though, the compression and bottom phases are best associated with the lightest exercise possible. Ascent and stop phases are best associated with mild, low-intensity exercise. Exercise that is aggressive and/or stimulates substantial joint-loading is almost always undesirable at any point near or during a dive.
Finally, the post-dive period is a good time to take a nap or relax over lunch. Both decompression and mental health can be helped by an extended period of relaxation between the end of the dive and the start of equipment shifting and/or racing on to the next activity.
In summary, 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 24 hours on either side of diving activity. Any exercise within 24 hours of diving should involve the lowest possible joint forces.References