Diving and regular exercise

Q: How is a dive professional supposed to stay in shape when we are advised to avoid vigorous exercise within 24 hours of diving? What kind of exercise is recommended for a divemaster or instructor who dives daily?
A: The problem you describe is, unfortunately, something of an intractable one. There is no easy solution. A compromise is almost always required. The simplest rule is that the highest-intensity exercise should be separated from diving, particularly from more extreme dives.
Some runners run every day regardless of other activities. The first recommendation for such people is that they dive very conservatively. This advice is by itself a problem since it is difficult to quantify “conservative” and the spirit of the recommendation is not generally understood in the diving community. Diving within the limits of a dive computer or table does not necessarily constitute conservatism. There are a variety of different limits and many divers have developed symptoms while adhering to them. Computers or tables provide estimates for a variety of people and exposures based on limited input.
A major challenge in appreciating the risk of decompression sickness (DCS) is its probabilistic nature. The fact that a diver might tolerate a given exposure once, twice or 10 times without incident does not mean the exposure is safe. If DCS results from the 100th exposure, this is not an undeserved hit – the diver simply ended up on the wrong side of the probability line that day.
Humans have a tendency to let good habits erode when nothing bad happens. We tend to increase our driving speed and push depth and/or time limits on dives. Furthermore, we often fail to appreciate that we are not being as conservative as we once were. This can lead to surprise when things go wrong.
This surprise can create a tendency to look for some factor to blame. With DCS, dehydration is often the scapegoat. The reality in most cases is that a similar state of hydration probably existed on many other dives. The real problem with this tendency is that it may encourage the diver to ignore the depth-time profile, which is by far the most important factor. While it can be comforting to identify a simple cause, it is a disservice to safety. The risk of DCS is affected by a large number of factors acting in complicated concert. True conservatism is required to increase the likelihood of consistently safe outcomes.
The daily runner will have a sense of the normal pains and discomfort associated with his or her exercise. Atypical pain or discomfort in a diver will raise suspicion of a decompression injury. Again, the ideal choice for this person would be to limit diving to conservative exposures. The next best choice would be to fit in the intense physical activity as far from diving as possible. It is safest to limit physical activity to that with very low joint forces – the closer to diving, the lower the forces. Modest swimming, for example, involves much lower joint forces than running. Cycling can also involve lower joint forces than running. These are not absolutes, though. It is not enough to choose an activity that might have low joint forces; it is necessary to practise it in a way that ensures low joint forces.
The practical approach is to separate physical activity from diving, with the lowest-intensity exercise closest to the diving. Swimming and walking typically produce less strain than intense cycling or running. High and repetitive joint forces should be minimised. The diver should be mindful of the activity level and honestly appraise the risk. By making small decisions that consistently favour the slightly safer option over the slightly more aggressive, an adequate safety buffer can be created.
This is not a simple answer, but reality is messy. Exercise, especially intense exercise, can increase the effective decompression stress. If it is not avoided, an honest appraisal of conditions and actions is important to control the risk. If a problem does develop, it is best to skip the denial and blame phases. DCS can and does happen, often following dives that were assumed to be safe.
Ultimately, each diver should appreciate the risks, work to control them and accept that diving involves complicated hazards. Getting bent should not be considered a personal failing. Being open to the possibility of DCS can start a diver down a very positive road of preparedness and action to reduce risk at every opportunity. Employ physical activity thoughtfully; ultimately the self-aware and self-critical (honest) diver will likely end up being the safest one.
 - Neal W. Pollock, Ph.D.