Physical exercise strengthens the body by improving its structure and function. Lack of exercise lessens the capacity to move and to resist stress.
Exercise is "physical" only in the sense that muscular action meets resistance and overcomes force. Exercise also involves mental and emotional activity and leads to a feeling of well-being.
Basically, there are two types of exercise: dynamic, or isotonic, and static, or isometric.
Dynamic exercise, such as calisthenics, involves moving muscles against some resistance.
Static exercises involve producing tension in motionless muscles and includes such activities as contracting the abdominal muscles when lying on one's back.
Minimum Requirements to Prevent Bodily Deterioration
There are four suggested guidelines for the maintenance of normal body structure and function. First, the body must expend through muscular activity at least 300 calories per day. This number of calories is used by such activities as walking at a brisk rate for one hour or playing golf leisurely for four hours. However, a busy person, if he walks, climbs, lifts, or carries an average of five minutes every hour requires no special exercise to use the minimum 300 calories a day. It is through expending calories that exercise helps to combat obesity. Use of less than 300 calories per day promotes the storage of body fat unless compensated for by a starvation diet when the caloric (food) intake is greatly reduced.
Second, the heart must accelerate above 110 beats per minute for at least five minutes each day to preserve normal heart function. Brisk walking or stair climbing will do this if prolonged enough to require circulatory and respiratory adjustments.
Third, the muscles must work at more than half their maximum tension at least every other day to maintain their strength. This can be accomplished by lifting a fairly heavy load- for example, a sack of groceries. It is the weight, not the number of lifts or length of time the object is carried that strengthens the muscles.
Fourth, the body joints should move through their maximum range of motion at least twice a week to keep connective tissues flexible- for example, the arms should be swung around their full range of movement.
To avoid injury and fatigue, one should start exercise training at a level slightly above that of the daily routine. The force, duration, and frequency of the training load should increase gradually. A period of four to eight weeks is required to elevate fitness from low to high levels. The mere repetition of moderate exercise has little effect on training. It is the amount of work done in each time period that determines the rate of training.
Effects of Exercise
The mechanisms by which exercise improves structure and function of the body involve subtle changes in the metabolic, nervous, skeletal, muscular, respiratory, and circulatory systems. In early stages, improvement results from lessening of waste motion. Further improvements come from better coordination as respiratory and circulatory systems adjust. Finally, improvements in the cellular structure of muscles, nerves, blood vessels, and bones bring training near the organism's capacity. An important effect of exercise is an increase in the body's oxygen uptake and consequently an increase in the body's ability to perform work. As exercise training progresses, there is a gradual increase in the lungs' ability to take in oxygen from the air and in the circulatory system's ability to pump and carry oxygen-laden blood to the working muscles. Dangers of Excessive Exercise. It is doubtful that a healthy organism can be damaged by exercise. Transient discomfort, such as a "stitch," or pain in the side, muscular aches, or shortness of breath are normal. It is well to feel the heart pounding in the chest, but when the pulse pounds in the head, one should rest. One should seek medical advice if any of the following symptoms persist after exercise: pains in the chest, severe shortness of breath, dizziness or faintness, fatigue, or an unwell feeling.