If you want to dive, you need to be ready. Readiness entails medical, psychological and physical fitness, appropriate knowledge and adequate physical skills. If you exercise regularly at an intensity that keeps your heart rate above 70 percent of maximum or so for more than 90 minutes per week, it is a good bet that you are physically fit enough to dive recreationally under a variety of conditions. Diving activity alone, however, will likely not be enough to constitute regular exercise. In addition, exercise conducted during or close to diving has implications for safety. So, what are the recommendations for exercise and diving? Read on.
By Neal Pollock, Ph.D.
Physical fitness for diving
Divers need to have sufficient strength and aerobic capacity reserves to meet both the normal and reasonable exceptional demands of diving in their chosen environment.7 Sadly, the hope that regular diving activity will be sufficient to maintain physical fitness, while heartfelt, is likely not realistic. Several issues important in juggling diving and exercise are discussed here. Physical fitness is maintained when the intensity and frequency of exercise aresufficient to protect the body’s capacity — the array of biochemical and physiological capacities that determine a fitness limit. Physical fitness is improved when the exercise load exceeds the body’s current capacity and a training effect is established. Most training programs rely on progressive overload — the incremental increase in training intensity to continue the drive to adapt at a pace that can be tolerated. Exceeding the threshold for maintenance or improvement of fitness, as desired, makes for an effective workout.
While a diver’s physical strength can be tested by carrying tanks and related gear, the duration of the effort is typically too short to constitute an effective workout. The aerobic demands of most well-planned dives are even less likely to reach the intensity to protect even a moderate aerobic capacity. Ultimately, the diver has to do something outside of normal diving to maintain or improve his or her fitness level.
Many individuals take their physical fitness for granted; this often leads to a surprise when one day their capacity is clearly not enough to complete an intended task. Faced with benign neglect, strength and aerobic capacity tend to peak somewhere in the early 20s for most people. Producing an effective training stimulus in the teens and 20s is much easier than it is later in life. If one does not dedicate time and effort to maintain fitness, the burden that was once no problem can become a big problem. Add to this the normal evolution of age-related medical issues, and the importance of attending to health and physical fitness becomes much more apparent.
There are additional fitness issues directly relevant to diving physiology. While the data are incomplete, physical fitness has been associated with fewer post-decompression bubbles in humans.2,8 While bubbles are not equated with decompression sickness, it is accepted that lower bubble counts indicate a reduced degree of decompression stress. Experiencing less decompression stress on any dive is definitely a good thing. Animal models have also demonstrated a lower incidence and reduced severity of DCS for trained versus untrained subjects.1,10 Ultimately, it may be clear that sound physical fitness is desirable for decompression safety as well as for physical competence, which is the ability to meet the physical demands of a situation.
Timing of exercise and diving
After accepting the need for regular exercise to maintain or improve physical fitness, the next issue concerns the timing of exercise training and diving. Scheduling outside physical fitness activities can be problematic when someone dives frequently. 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, or 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 microicronuclei 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 singleminded, 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 flipside, light exercise during the decompression phase (including safety or decompression stops) increases inert gas elimination and reduces risk. The caveat regarding 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 confer 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 it easy. Both decompression safety 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 avoided 24 hours on either side of diving activity. Any exercise within 24 hours of diving should involve the lowest possible joint forces.
About the Author
Neal Pollock, Ph.D., is a member of DAN research and a research physiologist at the Center for Hyperbaric Medicine and Environmental Physiology, Duke University Medical Center, in Durham, N.C.
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