DAN Medical Frequently Asked Questions

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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.

Physical activities are commonly classified by intensity into one of the following four categories:

  • Sedentary behavior: Sedentary behavior refers to activities that do not substantially increase one's heart rate or energy expenditure above the resting level; included in this category are activities such as sleeping, sitting, lying down and watching television. Such activities involve an energy expenditure of 1.0 to 1.5 METs.

  • Light-intensity physical activity: Light physical activity — which is often grouped with sedentary behavior but is, in fact, a distinct activity level — involves an energy expenditure of between 1.6 and 2.9 METs and raises the heart rate to less than 50 percent of one's maximum heart rate. It encompasses activities such as slow walking, deskwork, cooking and washing dishes.

  • Moderate-intensity physical activity: Physical activity that increases the heart rate to between 50 percent and 70 percent of one's maximum heart rate is considered to be of moderate intensity. For example, 50-year-olds have an estimated maximum heart rate of 170 beats per minute (bpm), so the 50-percent and 70-percent levels would be 85 bpm and 119 bpm. That means a moderate-intensity activity for 50-year-olds is one that keeps their heart rate between 85 bpm and 119 bpm. By contrast, 30-year-olds have an estimated maximum heart rate of 190 bpm, making a moderate-intensity activity one that raises their heart rate to between 95 bpm and 133 bpm.

  • Vigorous-intensity physical activity: A vigorous-intensity activity is one that increases the heart rate to between 70 percent and 85 percent of one's maximum heart rate. For 60-year-olds, that would be between 122 bpm and 136 bpm; for 25-year-olds, it would be between 136 bpm and 167 bpm.

Detailed physical activity recommendations can be found at
cdc.gov/physicalactivity/everyone/guidelines. Engaging in physical activity is beneficial for one's health, but making the transition from a sedentary lifestyle to being physically active, or increasing one's accustomed level of activity, may be associated with increased risk — especially in individuals with preexisting heart disease. Scuba diving?typically involves moderate-intensity physical activity, but situations can occur that require high-intensity activity. In addition, scuba diving challenges the cardiovascular system in a variety of ways that may be life-threatening for individuals with heart disease or a low capacity for exercise.

A common pre-activity screening tool is the Recreational Scuba Training Council (RSTC) Medical Statement and Guidelines. The RSTC questionnaire asks about your medical history as well as symptoms and signs of chronic and acute diseases. If prospective divers have any of the listed conditions, they are advised to consult with a physician to obtain a medical evaluation of their fitness to dive. Most dive operators use the RSTC form to screen customers, and if you check any conditions that call for medical evaluation but cannot present documentation of a recent exam that has cleared you for diving, you may be unable to dive. So you should complete the RSTC Medical Statement in advance of any trip during which you plan to dive and, if necessary, obtain a written evaluation from a physician knowledgeable about diving medicine — and take it with you on your trip.

And remember that it is of the utmost importance that you be honest in filling out the questionnaire: You hold the keys to your safe participation in any physical activity, including scuba diving.

In addition, regardless of their medical condition, men age 45 and older and women age 50 and older are advised to review their health annually with their primary-care physician. And all divers with any risk factors for cardiac disease should see their primary-care physician before engaging in diving and should be sure to follow any advice they're given.

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