Physical activity is any activity that causes your body to work harder than normal. The actual amount of physical activity you need depends on your fitness goals, whether you are trying to lose weight, and how fit you are right now.

Physical activity can help you:

• Burn calories and reduce body fat
• Reduce your appetite
• Keep your current weight and control it

For the purpose of weight loss, physical activity works best when you also reduce the amount of calories you take in from food and drinks.

The number of calories burned during physical activity depends on:

• The amount of time you spend 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 burn more calories 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 your body uses when it is at rest. BMR accounts for most of your calorie use. Your basal metabolic rate is based on things your body always does such as breathing, breaking down food, and keeping your heart and brain working. Your age, sex, body weight, and level of physical activity affect 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 for approximately 48 hours after the activity. This means, for example, that after the physical activity, when a person is sitting 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 shows that the decrease in appetite after physical activity is greater in individuals who are obese than in individuals who are at their right body weight.

LOSS OF BODY FAT

When losing weight just by taking in less calories, a person loses a quarter of his or her lean body mass, and three quarters 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 reached with a combination of calorie reduction and physical activity is more effective. For keeping a desirable body weight, a maintenance level of calories along with physical activity is recommended. This helps to preserve lean body mass and muscle tone.

RECOMMENDATIONS

For losing or maintaining weight:

• Try to do some form of physical activity at least three times a week. Increasing it to four to five times a week is even more helpful. Spread out the physical activity through the week rather than doing it on three or four consecutive days, to reduce the risk of 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 safely for a long period of time. If an exercise is too hard, 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 help in developing and maintaining fitness. If physical activity is stopped, 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.

BENEFITS

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 better, thereby helping with weight loss and weight maintenance. It can increase basal metabolic rate, reduces appetite, and help in the reduction of body fat.

SIDE EFFECTS

Physical activity should be done at a rate that is right for the person. An evaluation by an exercise physiologist is helpful, in order to to avoid injuries. Injuries can occur if physical activity is started without much consideration as to the type or length of the activity, and the physical condition of the person.