Physical activity; Exercise
Physical activity is any activity that causes your body to work harder than normal. However, the actual amount of physical activity you need depends on your individual fitness goals, whether you are trying to lose weight, and how fit you currently are.
Physical activity can help you:
- Burn calories and reduce body fat.
- Reduce your appetite.
- Maintain and control your weight.
For the purpose of weight loss, physical activity works best when you also reduce your intake of calories.
The number of calories burned is dependent on:
- The amount of time spent on physical activity. For example, walking for 45 minutes will burn more calories than walking for 20 minutes.
- Your body weight. For example, a 250-pound person will expend more energy walking for 30 minutes than a 185-pound person.
- Pace: For example, walking 3 miles per hour will burn more calories than walking 1.5 miles per hour.
BASAL METABOLIC RATE
Your basal metabolic rate (BMR) is the number of calories used by your body when it is at rest. BMR accounts for most of your calorie use. Your basal metabolic rate is based on body functions such as breathing, digestion, heartbeat, and brain function. Your age, sex, body weight, and level of physical activity impact the basal metabolic rate. Basal metabolic rate increases with the amount of muscle tissue you have, and it reduces with age.
Along with burning more calories, physical activity increases the BMR, and the BMR can remain increased after 30 minutes of moderate physical activity. For many people the basal metabolic rate can be increased 10% for approximately 48 hours after the activity. This means, for example, even after the physical activity, when a person is sedentary and watching television, the body is using more calories than usual.
EFFECT ON APPETITE
Physical activity at a moderate rate does not increase the appetite. In some situations, the appetite will actually decrease. Research indicates that the decrease in appetite after physical activity is greater in individuals who are obese than in individuals who are at their desirable body weight.
LOSS OF BODY FAT
When losing weight through calorie reduction alone, a person loses 25% of his or her lean body mass and 75% of his or her body fat. Combining calorie reduction with physical activity can result in loss of 98% of body fat. Weight loss that is achieved with a combination of calorie restriction and physical activity is more effective. For maintenance of desirable body weight, a maintenance level of calories along with physical activity is recommended to preserve lean body mass and muscle tone.
For losing or maintaining weight:
- Pursue physical activity at least three times a week. Increasing it to four to five times a week is even more beneficial. Spread out the physical activity through the week rather than doing it on three or four consecutive days to decrease the risk of related injuries.
- The target heart rate during physical activity should be 60 to 90% of the maximum heart rate.
To calculate the target heart rate, use the following formula:
1. 220(beats per minute) minus age = maximum heart rate.
2. Maximum heart rate multiplied by the intensity level = target heart rate.
For example, a 50-year old woman exercising at 60% maximum would use the following calculation:
1. 220 - 50 = 170 (maximum heart rate)
2. 170 X 60% = 102 (target heart rate)
This is her target heart rate regardless of the type of physical activity she elects to do.
Physical activity at 60 to 70% of the maximum heart rate can be continued at a safe rate for a long period of time. If an exercise is too strenuous, conversation cannot be carried on during the physical activity (the person is out of breath).
According to the American College of Sports Medicine, physical activity of less than 2 times a week at less than 60% of the maximum heart rate, and for less than 10 minutes per day, does not assist in developing and maintaining fitness. If physical activity is discontinued, the fitness benefits are completely lost. Within 2 to 3 weeks the level of fitness is reduced, and within 3 to 8 months it is completely lost, and the person has to restart again.
Twenty minutes of continuous aerobic activity 3 days per week is recommended for weight loss. Examples of physical activity that are considered aerobic are: walking, running, jogging, hiking, swimming, bike riding, rowing, cross country skiing, and jumping rope.
Physical activity contributes to health by reducing the heart rate, decreasing the risk for cardiovascular disease, and reducing the amount of bone loss that is associated with age and osteoporosis. Physical activity also helps the body use calories more efficiently, thereby helping in weight loss and maintenance. It can increase basal metabolic rate, reduces appetite, and helps in the reduction of body fat.
Physical activity should be done at a rate that is appropriate for the person. An evaluation by an exercise physiologist is helpful to avoid injuries that can occur if physical activity is initiated without much consideration given to the type, duration of physical activity, and the physical condition of the person.
by Brenda A. Kuper, M.D.
All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.