February 2002 - "Flexibility" Flexibility, or range-of-movement (ROM), is determined by the structural limitations of the relevant joint, the mechanical properties of muscles and other soft tissues of the joint, neuromuscular processes that control muscle tension and length, the level of non-functional muscle tension in the same or other muscles and soft tissues and the pain threshold of the individual in approaching end of range. Two types of flexibility are identifiable: active flexibility and passive flexibility. Active refers to the maximum ROM that can be produced under active muscular control for a particular degree of freedom of any joint, whereas passive refers to the maximum ROM that can be produced by imposition of an external force without causing joint injury. At this point it is relevant to point out that stretching and flexibility training are not necessarily synonymous. Some flexibility exercises are not stretching exercises although they increase range of movement. On the other hand, many stretching exercises do not pay any deliberate attention to neuromuscular processes and tend to concentrate on eliciting structural changes in the soft tissues. Thus, static stretches may actually change the length of the muscle complex, but have an inadequate effect on the dynamic range of movement required in a given physical activity. Therefore, it is vitally important to distinguish between the different types of stretching and flexibility exercises in order to utilize the most appropriate and effective balance of static and dynamic means of increasing functional ROM into an overall training program. For sports participant's active flexibility is by far the more important, even though passive flexibility provides a protective reserve if a joint is unexpectedly stressed beyond its normal operational. Experience has led to recognition for four traditional categories of stretching: static, ballistic, passive and contract-relax (or PNF - proprioceptive neuromuscular facilitation) stretching. Furthermore, a combination of stretching and weight-training exercises as a supplement to a sprint-training program produces significantly greater increases in speed over an un-supplemented sprint program. 1. Static Stretching: Free Static Stretching imposes no external loading to increase ROM. Passive Static Stretching imposes external loading on relaxed or isometrically contracted muscles. 2. Dynamic Stretching: Ballistic Stretching imposes momentum to exceed static ROM on the relaxed or the contracted muscle complex. The ballistic action may be done slowly or rapidly. Active Stretching involves continuous muscle activity to exceed the static ROM, as encountered during normal full-range sporting activities. PNF Stretching methods, which involve intermittent or continuous phases of static or dynamic muscle action, as well as relaxation or passive movement in specific patterns of activation and relaxation. Plyometric (Impulsive) Stretching involves rapid termination of eccentric loading followed by a brief isometric phase and an explosive rebound relying on stored elastic energy and powerful reflex muscle contraction. This 'stretch-shortening' action is not intended to increase ROM, but to use specific stretching phenomena to increase speed-strength of movement for a specific sporting purpose. It may also be viewed as a form of ballistic stretching done impulsively or explosively. The specificity of exercise indicates that each one of these categories of stretching may be used effectively and safely for specific subjects at a particular stage of training to achieve optimal stability and mobility. Active and PNF stretching involving progressive muscle contraction in specific patterns of movement against external loading over the full range of movement and beyond the static ROM seem to offer the most effective means of improving full-range functional performance in sport and exercise. This intensive type of neuromuscular training needs to be applied sparingly among advanced, well-prepared athletes by experienced coaches if it is not to produce overload shortening before stretch activation. It is well known that prior stretching of the muscle decreases the isometric and maximal force that a muscle can produce. For the competitive athlete or rehabilitating patient, static stretching is insufficient to develop the full range of movement strength, power, mobility and stability required in sport. It must be combined with high intensity static and dynamic activities to condition the tissues, full-range resistance training to increase muscle strength, and low-intensity cardiovascular and muscle endurance activity to enhance circulatory efficiency. After all, it is active flexibility of the appropriate degrees of joint freedom, which correlates most strongly with sporting proficiency and resistance to injury. It has been shown that: * The level of joint mobility generally relates strongly to sporting proficiency. The higher the level of sporting proficiency, the greater is passive and active flexibility. * The pattern and range of joint mobility is sport specific. For example in swimmers, the greatest shoulder and ankle mobility occurs in backstroke and butterfly specialists, whereas breaststroke swimmers have the lowest flexibility in these joints. Breaststroke swimmers, however, have the greatest range of hip and knee mobility. In track-and-field athletics, throwers, display the greatest level of shoulder mobility, while the greatest hip flexibility is found among hurdlers. Since active flexibility is a function of soft tissue mechanical stiffness and length (see Ch 1.6.4), as well as the strength of the muscles to move a joint to the limit of its range, any stretching routine should identify which of these factors demands most emphasis in improving active flexibility. Static stretching methods are used where the emphasis needs to be on tissue qualities, whereas dynamic methods are essential for rectifying deficits in full range strength performance. However, it is not only active flexibility, but also active functional range of movement in the specific sporting action that is of central importance to sporting proficiency.