Being physically fit can be important, and sometimes crucial, for dive safety. Physical fitness plays a role in both regular dive activities and emergent events. A quick and effective response to sudden demands can often quickly and easily resolve a situation, while an insufficient response can prolong or exacerbate it.
Scheduling exercise may not be simple though. The general recommendation is to avoid vigorous exercise within 24 hours of diving. While the restriction might not be an issue for casual divers, it can present active divers with a conundrum: How do you exercise if you dive most days? There is no simple solution, but understanding the factors can help with decision-making.
Both predive and postdive exercise can worsen decompression stress. While technology does not yet exist to directly measure the effects at a tissue level, predive exercise likely promotes the activity of micronuclei, the seed sites from which decompression-induced bubbles form. The effect may be due to the small-scale tissue damage that results from exercise, especially exercise involving high-impact forces.
Postdive exercise has additional implications due to tissue supersaturation. Tissues holding more dissolved gas than the ambient environment are susceptible to bubble formation, particularly when physical forces are added to the mix. Once formed, bubbles act as irritants, driving a biochemical cascade that promotes inflammatory responses. To visualize what is happening in the tissues, picture opening a can of soda after shaking it.
Exercise, especially intense exercise, increases decompression stress. Exercise that involves repetitive high joint forces is likely the most provocative, but lower intensities can still be problematic.
Generally, running is worse for decompression stress than walking due to the high and repetitive impact forces. Walking is not benign though, since the entire body weight (plus gear immediately postdive) loads the lower body. The legs effectively become bubble-producing machines.
Decompression research conducted for spacewalking astronauts offers a good example. Decompression from ground level to the low suit pressure creates substantial decompression stress. In a series of studies, subjects who did not walk at all during an experimental day experienced no decompression sickness (DCS). When subjects completed the same protocol with the addition of several short bouts of relaxed walking in place while in a supersaturated state, the DCS rate jumped to 20%.1
Non-weight-bearing activities are safer since they involve less impact stress. Cycling is less stressful than running, but the stress rises with increased resistance gearing or hill climbing. Swimming is generally less stressful than cycling, but the effect can be complicated. A relaxed flutter kick will produce relatively little force in the legs, while a forceful whip kick can generate more. Relaxed breaststroke and back crawl will generate less force in the arms than butterfly or a forceful front crawl.
There will always be a continuum of stress depending on loading, effort, and individual economy of motion. It is not enough to choose an activity that might have low joint forces or minimal strain; it is necessary to practice activities in a way that keeps the stress as low as feasible.
Current technology does not let us quantify the true decompression risk or the duration of the risk window, so thoughtful decision-making is necessary. There should be a substantial separation between physical activity and diving. Decompression stress is an invisible hazard, with a potentially fine but variable line between feeling normal and a bad outcome.
Safety buffers are important, especially when you can never fully avoid dive-related exercise. Exiting the water, especially when wearing full equipment, creates substantial stress when tissue supersaturation is high, which is the greatest risk condition. Strategies to minimize or delay postdive exercise can help, including longer decompression stops, rest periods on the surface before exiting the water (preferably while breathing oxygen-rich gas mixtures), gear removal prior to exit, and the aid of tenders or, if available, elevators to reduce the physical strain on divers.
Divers should consider the intensity of the exercise and the decompression stress of the dive to determine a reasonable interval between exercise and diving. The higher the exercise intensity and the more severe the decompression stress, the longer you should wait.
The 24-hour interval recommendation offers simple guidance for those who dive occasionally, but it may be unrealistic for the most active divers. Compromise will often be necessary. Exercising with the lowest joint forces and intensity can help, as can schedules that put the more intense exercise closest to the lowest decompression stress dives.
Modern tools can help determine the lowest decompression stress dives. Gradient factors (GFs) will be familiar to many who use dive computers employing the Bühlmann decompression algorithm. Displaying surface GF — the value if you surfaced immediately — at the end of the dive offers a simple way to compare the postdive decompression stress of different dives. The lower the value, the better. Modest profile changes, primarily increasing shallow decompression stop time, can help bring down the final numbers.
People who exercise in conjunction with diving, even with seemingly reasonable time between activities, should be aware of the increased risk and stay alert to any adverse effects. Most chronic exercisers will recognize the normal aches and discomfort associated with their activity. Atypical pain or discomfort while diving should raise the possibility of a decompression injury.
One aspect to consider is that the tolerance for decompression stress and exercise can vary individually. Patterns of practice that are fine for one diver may be problematic for another. It is important to calibrate group activities to those who may be the most sensitive.
You also have to balance the risk of exercise against the risk of not exercising. Sound physical fitness improves readiness, and there is evidence that it may moderately increase the resistance to decompression stress. Physical fitness should be part of the normal preparations for all divers, but care in planning diving, physical fitness activity, and ongoing self-assessment can help ensure the best reality.
Ultimately, divers should be well-informed, mindful of both decompression and exercise strategies, and able to honestly appraise the risks. Establishing a normal practice of making decisions that consistently favor more conservative options can help create safety buffers to reduce physical and psychological stress.
Referensi
1. Conkin J, Pollock NW, Natoli MJ, Martina SD, Wessell JH, Gernhardt ML. Venous gas emboli and ambulation at 4.3 psia. Aerosp Med Human Perf. 2017 Apr 1; 88(4):370-6.
doi: 10.3357/AMHP.4733.2017.
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