How much physical activity is needed for health benefits? Is more always better? What type of activity has the best health benefits? What intensity of exercise has the best health benefits? Can too much exercise be unhealthy?
The answers to all of these questions have some known and some unknown components. As long as research is being conducted on physical activity and health, then we won't have all the answers. Depending on whether you are a cancer survivor, are living with Type II diabetes, are obese, have a genetic predisposition to heart disease, or are a full-time athlete is likely to have a profound effect on the answers to these types of questions. Finding the right combination of frequency, intensity, and time (F.I.T.) of physical activity that is personalized to you for the best health benefits is no simple task. But, thankfully there are a number of useful and generally safe guidelines and recommendations available.
In North America, two organizations that preoccupy themselves with physical activity and health are the American College of Sports Medicine (ACSM) and the Canadian Society for Exercise Physiology (CSEP). Members of both of these organizations are involved in research, education, and public service in relation to physical activity and health, and both organizations provide specific guidelines on the recommended amounts and intensities of exercise that are beneficial to health.
Many chronic diseases are multi-factorial in their causes. Typically, things such as genetics, smoking, physical activity, and nutrition are all contributing factors in determining your risk of a particular chronic lifestyle-related disease (e.g. Type II diabetes, heart disease, stroke, some cancers, chronic obstructive pulmonary disease or COPD). The goal of including regular physical activity in your lifestyle with respect to heatlh is really two-fold: 1) to remove physical inactivity as a risk factor for these types of diseases; and 2) to increase awareness of all lifestyle factors and increase your chances of an overall healthy lifestyle (people who are active are also more likely to be proactive about not smoking, about proper nutrition, etc.). So, the relevant question becomes, how much physical activity does it take to remove physical inactivity as a risk factor for chronic diseases? As you may imagine, the answer varies with the person and with the condition, but the typical guidelines for healthy individuals are as follows.
ACSM's webpage provides a link to the physical activity guidelines for Americans. As you can see, the ACSM / American Heart Association guidlines are essentially to include 150 minutes of moderate intensity exercise per week. This is roughly broken down into recommendations of 30 minutes of moderate intensity cardio work 5 days per week OR 20 minutes of intense cardio work 3 days per week, AND 8 - 10 strength training exercises per week with 8 - 12 repetitions of each exercise.
Similarly, the CSEP webpage has a link to their physical activity guidelines for Canadians. Adults (aged 18 - 64) are recommended to achieve at least 150 minutes of moderate to vigorous intensity aerobic activity (i.e. cardio work) per week, in bouts of 10 minutes or more, AND 2 days per week of muscle and bone strengthening exercises (resistance work).
There is some debate over whether more than this has health benefits, and the reason it continues to be debated is likely because it depends which aspect of health you are referring to. For obesity prevention, undoubtedly greater acccumulation of activity is better, but for someone at risk for arthritis that might come at a cost. Chronic conditions like heart disease likely have a threshold of physical activity above which more exercise is unlikely to add much more of a preventive effect. But even this is debated and is likely individually variable. The above recommendations are the minimums, and you'll likely reduce your disease risk significantly if you meet those recommendations.
What is meant by moderate or vigorous intensity? The ACSM has a few links on intensity of exercise and CSEP defines moderate intensity activity as those that cause you to sweat a little and breathe harder such as brisk walking and bike riding, and vigorous intesnity activities as those that cause you to sweat and be out of breathe such as jogging and cross-country skiing. The easiest way to assess exercise intensty relatively accurately is to monitor your heart rate during exercise (this can be done either by pausing the activity and counting your pulse for 10 or 15 seconds and multiplying by 6 or 4 respectively) or by wearing a heart rate monitor. (More on heart rate and exercise intensity in a later post).
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