How Much Exercise we can do
The training effect of exercise depends on four variables
Frequency (how often a person exercises);
Intensity(how strenuously or, in some cases, at whatspeed);
Duration (how long);
Mode (type of exercise).
Aerobic activities allowing moderate exertion over long periods are best suited to improving the vital capacity of the lungs and the efficiency of the heart. But the other factors are open to considerable variation, depending on an individual’s health profile, schedule, interests, and motivation. Because these factors are interrelated, a change in one will mean an increase or decrease in the others. For example,walking a mile burns the same amount of calories as running a mile. In the running mode, the body works at a greater intensity but covers the ground more quickly, so the duration is shorter. Walking is done at a slower speed, so it takes longer to cover the same ground. A person running at 6 miles an hour will burn about 330 calories running 3 miles in 30 minutes. In order to burn approximately the same number of calories, a person walking at a lower intensity, 3 miles an hour, will either have to increase the duration to one hour or, at the same duration, to increase the frequency by dividing the walking into two half-hour sessions.
The following recommendations can guide healthy adults in achieving fitness
Exercise should be performed three to five days a week.
Intensity is expressed in terms of maximum heart rate, which is determined by subtracting one’s age from 220. The maximum heart rate for a 40-year-old, for example, would be 180 (220 – 40 = 180). Exercising at this maximum, however, would soon result in exhaustion.
Older people or those in poor health may start out in the low end of the range, while betterconditioned people may start at a higher range.
After six months or so, exercisers may want to work up to 75 to 85 percent of maximum heart rate. There is no need to exceed that; most people can stay in excellent condition at 75 percent.
Each session should last 20 to 60 minutes. Clearly, these guidelines leave the exerciser a great deal of latitude when developing an individual plan. Is it better to exercise closer to the minimum described, or closer to the maximum? Does exceeding the maximum described above yield any additional benefits, or can it do harm?
The answers to these questions will vary, depending upon a person’s initial fitness level, the potential for injury because of orthopedic or other conditions such as arthritis, and desired goals. The person who wants to improve from a good baseline level of conditioning to the status of a marathon runner will have very different requirements from the obese and completely sedentary individual who wishes to introduce some additional activity safely into his or her weekly routine.
In addition, the choice of a particular activity or set of activities will reflect personal abilities, circumstances, and preferences. In general, the greater the frequency, intensity, and duration of exercise, the more improvement can be expected in aerobic capacity. People who start an exercise program with a very low level of fitness will notice a greater initial improvement than those who start in better condition. Studies of the efficiency of exercise training tend to produce conflicting data, but they have generally shown that exercising for more than four to five days a week produces little additional cardiovascular benefit, while exercising fewer than three days a week is inadequate to achieve the training effect. The minimum level of exertion to start improving oxygen consumption is about 60 percent of maximum heart rate. This target heart rate changes with age and other factors.
Although it is the total amount of exercise that will improve and maintain fitness, the relationship of intensity and duration of exercise can be manipulated, as described earlier, to suit the individual exerciser.Of course, exercise must be done regularly on a longterm basis to consolidate the gains of the training period; missing a session occasionally won’t set one back significantly, but some studies have shown up to 50 percent loss in fitness improvement after 4 to 12 weeks without exercise.
The question “How much is enough?” raises another question: “How much is too much?” For people at high risk for coronary heart disease (CHD) or those who already have it, this is an issue to be resolved in consultation with the physician, based on medical test results such as the exercise stress test. For healthy adults, there is a slight risk of injury from intense and prolonged exercise that involves jumping or pounding, such as running, jogging, and rope-jumping, or from any activity that involves overuse of certain joints, muscles, and connective tissues. Graduated, balanced workouts with appropriate warm-ups and cool-downs are the best safeguards against injury.