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Wednesday, September 24, 2014
Physical activity guidelines: How much exercise do you need?
For general good health, the 2008 Physical Activity Guidelines for Americans recommends that adults get a minimum of 2-1/2 hours per week of moderate-intensity aerobic activity. (37) Yet many people may need more than 2-1/2 hours of moderate intensity activity a week to stay at a stable weight. (37)
The Women’s Health Study, for example, followed 34,000 middle-aged women for 13 years to see just how much physical activity they needed to stay within 5 pounds of their weight at the start of the study. Researchers found that women who were in the normal weight range at the start of the study needed the equivalent of an hour a day of physical activity to stay at a steady weight.(43)
If you are exercising mainly to lose weight, 30 minutes or so a day may be effective in conjunction with a healthy diet. (44)
If you currently don’t exercise and aren’t very active during the day, any increase in exercise or physical activity is good for you.
Aerobic physical activity—any activity that causes a noticeable increase in your heart rate—is especially beneficial for disease prevention.
Some studies show that walking briskly for even one to two hours a week (15 to 20 minutes a day) starts to decrease the chances of having a heart attack or stroke, developing diabetes, or dying prematurely.
You can combine moderate and vigorous exercise over the course of the week, and it’s fine to break up your activity into smaller bursts as long as you sustain the activity for at least 10 minutes.
Moderate-intensity aerobic activity is any activity that causes a slight but noticeable increase in breathing and heart rate. One way to gauge moderate activity is with the “talk test”—exercising hard enough to break a sweat but not so hard you can’t comfortably carry on a conversation.
Vigorous-intensity aerobic activity causes more rapid breathing and a greater increase in heart rate, but you should still be able to carry on a conversation—with shorter sentences.
Children and adolescents should get at least 1 hour or more a day of physical activity in age-appropriate activities, spending most of that engaged in moderate- or vigorous–intensity aerobic activities. They should partake in vigorous-intensity aerobic activity on at least three days of the week, and include muscle-strengthening and bone strengthening activities on at least three days of the week.
Healthy adults should get a minimum of 2-1/2 hours per week of moderate-intensity aerobic activity, or a minimum of 1-1/4 hours per week of vigorous-intensity aerobic activity, or a combination of the two. That could mean a brisk walk for 30 minutes a day, five days a week; a high-intensity spinning class one day for 45 minutes, plus a half hour jog another day; or some other combination of moderate and vigorous activity. Doubling the amount of activity (5 hours moderate- or 2-1/2 hours vigorous-intensity aerobic activity) provides even more health benefits. Adults should also aim to do muscle-strengthening activities at least two days a week.
Healthy older Adults should follow the guidelines for healthy adults. Older adults who cannot meet the guidelines for healthy adults because of chronic conditions should be as physically active as their abilities and conditions allow. People who have chronic conditions such as arthritis and type 2 diabetes should talk to a healthcare provider about the amount and type of activity that is best. Physical activity can help people manage chronic conditions, as long as the activities that individuals choose match their fitness level and abilities. Even just an hour a week of activity has health benefits. Older adults who are at risk of falling should include activities that promote balance. (37)
Strength training for all ages
Studies have shown strength training to increase lean body mass, decrease fat mass, and increase resting metabolic rate (a measurement of the amount of calories burned per day) in adults. (59, 60) While strength training on its own typically does not lead to weight loss, (61) its beneficial effects on body composition may make it easier to manage one’s weight and ultimately reduce the risk of disease, by slowing the gain of fat—especially abdominal fat. (62)
Muscle is metabolically active tissue; it utilizes calories to work, repair, and refuel itself. Fat, on the other hand, doesn’t use as much energy. We slowly lose muscle as part of the natural aging process, which means that the amount of calories we need each day starts to decrease, and it becomes easier to gain weight.
Strength training regularly helps preserve lean muscle tissue and can even rebuild some that has been lost already.
Weight training has also been shown to help fight osteoporosis. For example, a study in postmenopausal women examined whether regular strength training and high-impact aerobics sessions would help prevent osteoporosis. Researchers found that the women who participated in at least two sessions a week for three years were able to preserve bone mineral density at the spine and hip; over the same time period, a sedentary control group showed bone mineral density losses of 2 to 8 percent. (63)
In older populations, resistance training can help maintain the ability to perform functional tasks such as walking, rising from a chair, climbing stairs, and even carrying one’s own groceries. An emerging area of research suggests that muscular strength and fitness may also be important to reducing the risk of chronic disease and mortality, but more research is needed. (64-68)
A systematic review of 8 studies examining the effects of weight-bearing and resistance-based exercises on the bone mineral density (BMD) in older men found resistance training to be an effective strategy for preventing osteoporosis in this population. Resistance training was found to have more positive effects on BMD than walking, which has a lower impact. (69)
The Physical Activity Guidelines for Americans recommends that muscle strengthening activities be done at least two days a week. (37) Different types of strength training activities are best for different age groups.
When talking about the benefits of exercise, keeping the heart and blood vessels healthy usually gets most of the attention. For many individuals, though, stretching and strength training exercises may be just as important.
Strength training, also known as resistance training, weight training, or muscle-strengthening activity, is one of the most beneficial components of a fitness program.
Children and Adolescents: Choose unstructured activities rather than weight lifting exercises. (37)
Playing on playground equipment
Active Adults: Weight training is a familiar example, but there are other options: (37)
Calisthenics that use body weight for resistance (such as push-ups, pull-ups, and sit-ups)
Carrying heavy loads
Heavy gardening (such as digging or hoeing)
Older Adults: The guidelines for older adults are similar to those for adults; older adults who have chronic conditions should consult with a health care provider to set their activity goals. (37) Muscle strengthening activities in this age group include the following:
Digging, lifting, and carrying as part of gardening
Some yoga and tai chi exercises
Strength exercises done as part of a rehab program or physical therapy
Flexibility training or stretching exercise is another important part of overall fitness. It may help older adults preserve the range of motion they need to perform daily tasks and other physical activities. (70, 71)
The American Heart Association recommends that healthy adults engage in flexibility training two to three days per week, stretching major muscle and tendon groups. (60)
For older adults, the American Heart Association and American College of Sports Medicine recommend two days a week of flexibility training, in sessions at least 10 minutes long. (70) Older adults who are at risk of falling should also do exercises to improve their balance.
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