Dr. Kevin Yip

Dr Kevin Yip
Orthopaedic Surgeon

Featured on Channel NewsAsia

Training and exercising

Basic physical fitness

Good physical fitness is of the utmost importance in avoiding injury. Those whose basic fitness is below normal are more prone to injury both from trauma and from overuse.After a period of inactivity, the ability of the body tissues to utilize oxygen decreases noticeably. In one experiment, five healthy test subjects stayed in bed for 20 days without any physical activity whatsoever.This relatively short period of inactivity reduced their capacity to utilize oxygen by 20–45%.This and similar experiments demonstrate how quickly the body adapts to the physical demands made on it. When the demands are reduced there is a corresponding decrease in the cardiac output, muscle mass diminishes (hypotrophy), and blood volume decreases. The body is less efficient in transporting oxygen from the lungs to the tissues, and as a result the capacity of the muscles to convert nutrients into energy is reduced.

Basic physical fitness can be achieved by exercises and general physical activity continued throughout the year. All training aimed at achieving good basic physical fitness should progress gradually, and this applies above all to those who are no longer young. During a period of rehabilitation following illness, injury, or a break in training, it is important that a reasonable level of basic physical fitness is reached before competition is resumed.

The warm-up period

Warm-up exercises are designed to prepare the body for the ensuing sporting activity. They have two functions: to prevent injury, and to enhance performance.In a body at rest the blood flow to the muscles is low, and most of the small blood vessels supplying them are closed. When activity begins, the blood flow to the muscles increases as the vessels open. At rest 15–20% of the blood flow supplies muscles, while the corresponding figure after 10–12 minutes of exercise can be 70–90%. A muscle can achieve maximum performance only when all its blood vessels are functional.

Physical work increases the potential energy output and the temperature of the muscles, and this in turn leads to improved coordination with less likelihood of injury.A progressive warm-up leads to a marked decrease in the risk of injury and an enhanced performance,while at the same time providing some psychological preparation for the task to come. Warm-up exercises should begin with movements of the large muscle groups, as these are the main areas to which blood is redistributed.

After this general warm-up, more specialized exercises can begin. Runners, for example, should concentrate their warm-up on the muscles and joints of the lower limbs. Stretching of muscles and joints is essential, but heavy loads at the outer limits of joint movement should be avoided. The final stage of warm-up concentrates on technique, perhaps checking a run-up or practicing a sport-specific movement. The pace of the exercises can be gradually increased, and the warm-up sessions should last for at least 10–30 minutes, depending on the sport involved.

Depending on the circumstances surrounding the activity in question (such as temperature and humidity) it may be advantageous to put on a fresh shirt after a warm-up, to prevent the muscles from cooling too quickly as sweat evaporates. A tracksuit may also be advisable for warmth. The effect of the warm-up soon starts to wear off and ideally the time delay before competition should be no longer than 10 minutes. Warmup exercises should be completed before both training and competition, and clearly represent a major factor in preventing injury and enhancing performance.After training or competition, cooling-down exercises, such as gentle jogging, are desirable. Stretching should also be part of the cooling-down process if maximum benefit is to be achieved.

Effects of inactivity and training on tissues

The musculoskeletal system, comprising the bones and their associated joints, ligaments, muscles, tendons,nerves and blood vessels, undergoes qualitative changes in response to levels of physical activity.

Effects on bone

The bone structure of athletes who have been immobilized for some time or who have not exercised becomes decalcified. This weakens the bone, with increased risk for fracture. Immobilization stimulates bone resorption and depresses bone formation, resulting in osteoporosis. Of the total bone loss, 30% is due to increased bone resorption and about 70% to decreased bone formation. If weightbearing is allowed despite immobilization, bone loss is less than in non-weightbearing conditions. If the bone structure is exercised regularly by physical training, it adapts to increased demands and becomes more robust, though those parts that are subject to decreased stress may still undergo some weakening and degeneration.

These changes take place slowly during the rehabilitation period after injury and—most importantly—during prolonged, unbalanced training of children and young people. These changes can be permanent.There is a relationship between the different states of loading and tissue quality: during training, the lower the initial loading state, the faster and better the adaptation; during immobilization, the higher the initial loading state, the faster and more severe the demineralization. The reverse is true for both situations.

Effects on tendons

Inactivity and immobilization cause tendon hypotrophy, although at a slower rate than that of muscle. The tensile strength, elastic stiffness, and total weight of the tendon tissue decrease; the collagen fibers that compose the tendon become thinner and disoriented; and the crosslinks between the tendon fibrils may become smaller and reduce in number. Regular exercise can preserve the strength of the connective tissue and delay the degeneration that normally occurs with age. It also improves the mechanical properties (material composition) and the structural properties (breaking strength) of the tendon.

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