Regular physical activity and a healthy diet are necessary to stay fit and healthy. A balance of the calorie expenditure and calories consumed is essential for staying healthy. There are several ways to calculate the energy expenditure or calories burnt during different activities, metabolic equivalent of task (MET) unit being one such measure. METs tell us about the oxygen utilized by the body. Our body utilizes oxygen for cellular respiration, which is a process to generate energy. Thus, METs give an indication of energy expenditure in the body.
One MET is defined as the energy expenditure per minute for sitting quietly. This is approximately 3.5 mL of oxygen uptake per kilogram of body weight per minute (1.2 kcal/min for a 154-lbs adult). Thus, a 3-MET activity requires three times the energy expenditure of sitting quietly. This means that your METs increase with an increase in activity. This is a great way to know the intensity and hence the effectiveness of an exercise regimen. By knowing the METs for different physical activities, you can find out how many calories you need to consume for managing your weight based on your activity level. As METs are measured per unit of body weight, they can be used for people whose weights are different and without any need for complicated calculations. Calories burnt, however, differ with the weight of the individual even for the same kind of activity done for the same duration. Thus, if two individuals, one weighing 160 lbs and another weighing 200 lbs, walk at the same speed for 30 minutes, the one weighing more will burn more calories than the one weighing less.
METs can tell about your capacity for performing physical activity. Thus, the maximum METs you can achieve and sustain for a few minutes tell about your exercise capacity. The METs capacity is your upper limit of capacity to exercise and should not be confused with the recommended workout level. To stay fit, you must exercise at around 60-85% of your MET capacity. You can approach your maximum capacity only during interval training peaks. An improving MET value can indicate toward improvement in fitness level. If you have any underlying health conditions such as heart diseases, your doctor may suggest an upper limit for METs during physical activities. A study done at Harvard revealed that women with 21 MET-hours per week, equivalent to about 7 hours per week of brisk walking, were half as likely to develop colon cancer than those who got only 2 MET-hours per week (equivalent to walking slowly for 1 hour per week). According to the Centers for Disease Control and Prevention (CDC), any activity burning 3-5.9 METs is considered moderate-intensity physical activity. A vigorous physical activity burns 6.0 METs or more. The American Heart Association (AHA) suggests that an individual must have at least 150 minutes per week of moderate-intensity aerobic activity or 75 minutes per week of vigorous aerobic activity (or a combination of both), preferably spread throughout the week. This translates to 450-885 METs per week. AHA further stresses the fact that some physical activity is better than none. Thus, based upon your general health and underlying conditions, you can start with some form of physical activity and increase it gradually with time. Your target METs also vary according to your age and gender. METs can help classify activities into different categories:
- Sedentary activities: Use 1.5 or fewer METs. For example, lying down, sitting, or reclining
- Light-intensity activities: Use from 1.6 to 3.0 METs. For example, walking at a leisurely pace or standing in line at the billing counter.
- Moderate-intensity activities: Use from 3.0 to 6.0 METs. For example, brisk walking (2.5-4.2 mph), bicycling (5-9 mph), or ballroom dancing
- Vigorous-intensity activities: Use from 6.0+ METs. For example, circuit weight training, most competitive sports, or aerobics dancing
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