“Prolonging shallow stops — either safety or obligatory — is cheap insurance. Stay long, breathe easy.”
Medical and Physical Fitness
Poor medical and physical fitness can compromise your safety in general and may increase your risk of DCS. Definitive data are limited, but there is no question that it is prudent to maintain a high level of physical fitness [ad:media] and to dive progressively more conservatively as your fitness level declines. Safe diving is possible throughout much of a normal life span, but it is important for all divers to seek regular, objective evaluation of their capabilities and to adapt their diving practices accordingly. But even for divers who have transitioned from independent to more dependent forms of diving, in which they increasingly rely on the support of others, there will ultimately be a point at which they should hang up their fins.
Physical Activity Recommendations
Adults need two types of regular activity to maintain or improve their health—aerobics and strength training. The Centers for Disease Control and Prevention's 2008 Physical Activity Guidelines for Americans recommends at least two and a half hours a week of moderate-intensity aerobic exercise to achieve health benefits, and five hours a week to achieve additional fitness benefits. And just as important as engaging in aerobic exercise is doing muscle-strengthening activities at least two days a week.
While good health and physical fitness will not solve all problems, the foundation is an important one. An adequate physical reserve can allow a quick response to keep a small problem from becoming a serious one. Relevant scenarios can be easily imagined for almost any dive.
Regular aerobic exercise has many positive benefits. Cardiac reserve is the difference between the rate at which the heart pumps blood at rest and its maximum capacity. An increase in this reserve may make it easier to meet the physical demands of diving activity and stress. Blood values of cholesterol can improve, reducing susceptibility to heart disease. Insulin sensitivity can improve, reducing the risk of developing diabetes. While the data specific to diving are much more preliminary, there is also some evidence that higher levels of aerobic fitness may contribute to a reduced decompression stress.
Most individuals are aware that being fit can improve quality of life. A major problem, however, is that time takes a toll on us. The ease with which we maintain our fitness level in our 20s can be very different from the reality as decades pass. Aerobic fitness typically declines on an average of one percent per year after age 30. The important point is that while some decline may be unavoidable due to a gradual loss of muscle mass and a reduction in the metabolic activity of aging muscle, the rate can be slowed and the reserve range broadened by adopting healthy lifestyles as early as possible.
The physical fitness needed for diving will vary with the demands of the environment, the equipment, and the nature of the dive. The best strategy is to incorporate regular physical activity into your life to improve or preserve your capabilities, and to prolong your diving life. Do not count on diving to keep you physically fit. If done properly, it should be your relaxing time in the water. To maintain or build aerobic capacity and strength, swim, cycle, run, or do whatever other physical activities you can enjoy. The more fit you are, the longer you get to play.
Detailed physical activity recommendations can be found at [cdc.gov/physicalactivity/everyone/guidelines|http://www.cdc.gov/physicalactivity/everyone/guidelines].