FLEXIBILITY

Skeletal muscle consists of many muscle fibers (cells) arranged in parallel bundles. Muscles can grow in length and diameter, have the ability to contract and if relaxed, are very elastic. When a muscle contracts, two kinds of protein (actin and myosin) in its cells slide along one another. As a muscle is stretched beyond its normal resting length, its force of contraction gradually drops to zero at 175% of resting length. Diminishing strength of contraction is caused by decreasing amount of overlap between actin and myosin. Cutting off the flow of blood to the muscle reduces elasticity. Flexibility improves with increased flow of blood in stretched muscles.

Whole muscle is encased in a connective tissue sheath (epimisium), bundles and even single cells are also surrounded by the same tissue (perimisium and endomisium). Tension generated by muscle cells is transferred to the fibers of connective tissue. Tendons are cordlike extensions of this tissue. Collagen fibers, a major element of connective tissue, have great strength, no elasticity and cannot contract. These fibers are arranged in wavy bundles allowing motion until the slack of these bundles is taken up. Extension of a tendon beyond 4% of its length causes irreversible deformation. Improper use of isometric or eccentric tensions can put too much stress on collagen fibers damaging them and causing muscle soreness - a result of disintegration of collagen and release of hydroxyproline, one of its components, into the muscle. With age molecules of collagen change becoming more rigid and this is reflected in general body stiffness.

Joint capsule is a connective tissue sleeve completely surrounding each movable joint. Immobilisation for a few weeks causes chemical changes in collagen fibers of the joint capsule that will restrict flexibility. Ligaments holding joints together are made primarily of collagen fibers. They have more elastic fibers, made of protein elastic, than do tendons. Stretching ligaments leads to loose-jointness and can be effectively applied only with children. In adults, age related increase in rigidity of collagen fibers makes any stretches aimed at elongating ligaments hazardous. When children stretch ballistically or statically, their muscles do not contract as strongly as adult's and ligaments can be stretched. If a ligament is stretched more than 6% of its normal length it will tear. There is no need to stretch ligaments to perform even the most spectacular Tae Kwon-Do kicks. Natural range of motion is sufficient.

If stretching was started past the age when elongating ligaments was possible then difficulty can be encountered in touching the ground with the front of the thigh of the rear leg in a front split. This is not muscle but a ligament (lig. iliofemorale) running in front of the hip joint that is tightened by extension of the hip (posterior tilting of the pelvis or moving the thigh to the back while keeping the pelvis straight) that stops the thigh touching the ground. Flexing the hip (tilting the pelvis forwards or moving the thigh to the front) relaxes this ligament. To achieve a nice, flat split the hamstring of the front leg and the muscles of the lower back need to be stretched so that the pelvis can tilt forward while keeping the trunk upright.

A person unable to perform a complete side split but who can bring one of the thighs into the position it would have in relation to the hip in a side split, or at least get it much closer to this position than when spreading both legs at the same time should be able to perform a proper side split because no muscles run from one leg to the other. A simple test is to stand next to a chair and to rest one leg on the back of the chair in side split position whilst the other leg stays on the floor. Only reflective contraction of the muscles prevents a complete split with equal ease. Our reflexes are so arranged as to be useful in normal circumstances and when the legs slide sideways, tension of adductors and their synergists on both sides of the body is needed to maintain a good posture. In a side split not only do the legs spread sideways but the pelvis tilts forwards (push buttocks to the rear). In a side split with the feet pointing upwards, the pelvis is kept straight but the thighs rotate outwards. Alignment of the hips and thighs in both types of side split is the same. This split is not possible without either rotating the thighs outwards or tilting the pelvis forwards. This forward tilt (hip flexion) unwinds capsular ligaments of the hip, among them the pubofemoral ligament that resists excessive abduction. Spreading the legs without these additional movements twists and tightens ligaments of the hip and jams the thigh bones against the pelvis.

Relieving tension of muscles around the joint increases its range of motion. This means that only muscular tension prevents a person from doing the splits. Muscular tension has two components: tension generated by the contractile elements (muscle fibers) and the tension, present even in an inactive, denervated muscle, exerted by the connective tissues associated with it. The nervous system regulates tension and thus length of muscles by influencing the contractile element. The cells whose nerve fibers conduct signals to the muscles are called motoneurons. Other neurons contact and influence motoneurons. When motoneurons of one set of muscles are stimulated, motoneurons of muscles opposing them are inhibited. This is called reciprocal inhibition. It allows a person to move.

Muscles are usually long enough to allow for full range of motion in joints. It is nervous control of their tension that has to be reset for the muscles to show their full length. It is possible to use the inhibiting functions of the Golgi organs (located in the tendon at its junction with the muscle) by contracting a muscle before stretching it. This increases the amount of possible stretch. After reaching maximal stretch (maximal for the person at a given stage of training) tensing the muscle improves static strength in it.

DYNAMIC STRETCHING: Moving parts of the body, gradually increasing reach and/or speed of movement. There should be no bouncing or jerky movements.

STATIC ACTIVE STRETCHING: Moving the body into a stretch and holding it there by tension of muscles-agonists in this movement. Tension of these muscles helps to relax (reciprocal inhibition) muscles opposing them.

STATIC PASSIVE STRETCHING: Relaxing your body into a stretch and holding it their by the weight of your body or by other external force.