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Biomechanical considerations

The range of movement of a joint is normally limited by the articular surfaces, the ligaments, and the joint capsule, and by the length and flexibility of muscles and tendons. The ligaments and joint capsule are comparatively inelastic and are responsible for maintaining passive stability, while muscles and tendons control active stability.Muscles, tendons, and ligaments all contain collagen fibers. A tendon, for example, consists of 90% collagen fibers and 10% elastic fibers. The collagen fibers run parallel in tendons, in tendon attachments,and in the areas where they merge with muscles. They are under no tension at rest but are loaded and stretched during muscle contraction.Collagen tissue can be elastic (resilient) or plastic (pliable), and has a high viscosity (internal friction). The fact that it is both viscous and elastic means that the speed with which it is loaded is of importance. The faster a tendon is loaded, the stiffer (less elastic) and less pliable it becomes.During slow loading, on the other hand, there is an increase in its elastic and plastic properties.The collagen in tendons must be subjected to extension for at least 6 seconds for its plastic properties to change.

At temperatures of about 38 °C (100–101 °F) or just above normal body temperature, there is an increase in the elasticity and plasticity of collagen fibers, so a careful and thorough warm-up should be carried out before any flexibility training begins. Localized warming of tendons followed by slow stretching to the pain threshold results in extension of the collagen fibers of the tendons to their maximum length. The stretching should be carried out within 15–20 minutes of the application of local heat treatment, otherwise the warm-up effect will be lost.

Range of motion

Full, pain-free range of motion (ROM) is the goal of all rehabilitation programs. However, this need not be achieved completely before strengthening exercises are initiated as long as the exercises are pain-free.Range-of-motion exercises can be facilitated through the use of thermotherapy to limit pain and increase blood flow to the area, resulting in increased tissue extensibility. These exercises may be done passively or actively. Passive ROM exercises allow for early motion without the use of contractile tissues. Often in the early stages of rehabilitation, passive motion is indicated to allow for tissue healing; active motion may be painful. Active ROM exercises require muscular action for movement to occur. This is the method of choice as rehabilitation progresses and muscle activity is safe.


Flexibility, the ability to move a joint painlessly through its full range of motion, is an important goal of rehabilitation. Flexibility is believed to contribute to fluidity of movement patterns. Most agree that adequate flexibility is necessary for good performance and injury prevention, although this is based primarily on observation rather than research. Flexibility exercises should be designed to improve joint ROM. They include static stretching, proprioceptive neuromuscular facilitation techniques, and ballistic stretching.

Static stretching is an extremely effective and popular technique. This method involves passively stretching a muscle and holding it in its extended position for a period of 10–60 seconds (most often, 20 seconds). Static stretching is probably safer than ballistic stretching because the extensibility limits of involved muscles are less likely to be inadvertently exceeded. Training with static stretching should be an integral part of the rehabilitation program following an injury.

In most cases, it can begin soon after the injury occurs, although in cases of muscle or tendon rupture, it should be postponed until a doctor gives approval. Generally, static stretching can start when there is no local tenderness in the injured area and when static muscle contractions can be performed without pain. However, static stretching can be used to evaluate healing in an injured muscle or tendon by using the level of pain as a measure of the state of the healing process.

Proprioceptive neuromuscular facilitation (PNF) is a technique for use with flexibility exercises,involving a combination of alternating isometric and isotonic contractions and subsequent relaxation of both the agonist and antagonist muscle groups. The exercises are often performed with a partner, and consist of 10 seconds of contraction followed by 10 seconds of relaxation and stretching.Ballistic stretching involves repetitive, small-amplitude bouncing motions. It is generally accepted as less safe because of the quick stretches and somewhat uncontrolled forces within the muscle, which may exceed the limits of the muscle fiber.

However, used correctly, it can be effective.During any flexibility exercise, the involved muscles should be warm, and stretched slowly, and controlled to the point of slight resistance or tightness. In order to improve flexibility, each exercise should be performed daily, for five or six repetitions, held for a minimum of 20 seconds. Stretching should be included as part of a warm-up to prepare muscles for activity. Stretching after activity may prevent some muscle soreness and help increase flexibility by stretching loose, warm muscles.

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