Flexibility means to reach required or maximum joint rangle through muscle contraction or through the action of external forces. Each sports discipline requires a certain rangle of flexibility necessary for optimum performance of motor skills. Gymnasts need much bigger rangle of flexibility of hip joint than football players. Similarly, there are differences in flexibility ranges with an individual athlete in different joints or in the same joints of pair organs. The main factors which affect flexibility include:

• Physique of joints (the shape of the joint, muscle hypertrophy, the lay-out of muscle tissue, the type of muscles).
• Sufficient strength of muscles performing the movement in the point.
• Motor control (the cooperation of agonists, antagonists and sunergists).
• Individual condition of the athlete (age, sex, psychical condition, health condition, fatique).
• External conditions (temperature of the surroundings, time of the day, the quality of stretching).

A basic precondition necessary for flexibility development is relaxed muscle. Relaxation means the opposit of muscle contraction, i. e. “inactivity” of the muscle caused by a cease in the Central Nervous System.

Muscle contraction is caused by a neural impulse towards muscle fibre. The neural impulse releases calcium ions present in the muscle. If adenosintriphosphate (ATP), which represents fuel for skeletal muscles, is present, calcium ions bind with actin and myosine and form electrostatic bond. The formed bond can be compared to two counter-polarized magnets which pull on each other. As a consequence of such a bond, actin fibers are being dragged in between myosine fibers and the muscle fiber is shortened while tension in the muscle appears. The result of this process is muscle contraction. If muscle fibers do not receive any neural impulses, the muscle fibre stretches and tension decreases. An example of this is extension in the knee joint when during contraction of quadriceps femoris, hamstrings relax.

In skeletal muscles, there are two kinds of proprioreceptors (Golgi tendon bodies and muscle spindles) which provide information to the Central Nervous System on changing length of a muscle. Golgi bodies monitor all tension stages of muscle tension; however, they best perceive the tension caused by muscle contratio. Muscle spindles have two types of neural receptors. Primary receptors react to both dynamic and tonic stretching. Secondary neural receptors reacto only to tonic stretching. The reaction is determined by the length and speed of muscle stretching (e.g. in swing stretching). Tonic response is determined only by the length of the muscle (e.g. in static stretching).

Factors limiting muscle stretching

Stretch reflex is the basic function of nervous system; it maintains muscle stretching and reacts to sudden, unexpected muscle stretch. This relfex is a protection from injuries caused by dangerous muscle stretching. A typical example of this is patellar reflex: if patella is knocked on, muscle spindles, which are parallel to muscle fibers, are stretched, which results in stimulation of neural receptors. The consequence of this is neural impulse into quadriceps femoris which shortens. However, this reflex presents a problem for targeted stretching. Cease of stretch reflex presents a necessary precondition for stretching the muscle.

Factor supporting muscle stretching

Reciprocal inervation is enabled by synchronous control of muscle activity by the Central Nervous System. Muscles usually work in pairs; when one is shortened (biceps brachii), the other must be prolonged (triceps brachii) and vice versa. If there appears inervation and subsequent muscle contraction of one muscle, the other muscle is automatically relaxed. This phenomenon is used to achieve relaxation in muscles which we want to stretch. An example: if we want to stretch hamstrings, it is necessary to contract quadriceps femoris in the position of modifiable hurdle sitthing. Reciprocal inervation causes hamstring relaxation.

Myotatic inverse reflex is related to the protective function of Golgi bodies. If the intensity of muscle stretch exceeds critical limit, a reflex which ceases muscle stretch appear immediately, which causes immediate relaxation of the muscle and decrease in excessive stretch. Relaxation is a protection mechanism which prevents from tendon and muscle injuries which could otherwise appear in the form of their being torn off tentacles.

Flexibility development is based on intentional supression of factors which limit joint range and on introducing sitmuli which lead to maintaining or increasing the range. In practice, it is:

• necessary muscle relaxation
• stretching muscles and ligament tissue
• regulating reflexive actitivty of the muscle
• strengthening antagonists
• elimination muscle imbalance

There are several approaches to flexibility classification. In sports practice, static and dynamic flexibility is distunguished. Static flexibility is characterized by achieving maximum current movement rangle by slow movement. Dynamic flexibility is characteristic in repeated achieving maximum rangle by standard or increased speed. From the point of view of the causes of movement, we can differentiate active flexibility when limits are reached by active muscle contraction (concentric muschle contraction of quadriceps femori causes hamstring stretching). The movement range of passive flexibility is determined by actions of external forces (e.g. gravity action or with the help of a partner).

Training flexibility

Requirements for optimum level of flexibility spring from a specific sports discipline. Joint range must be on a level sufficient for allowing the athlete to strive for optimum performance of sports skills. A necessary precondition to increase joint range is a relaxed muscle. The sense of relaxing muscles is to regulate their reflexive activity and thus, relax its stretching prior to futher stretching as much as possible. Stretching muscles without sufficient stretching is not efficient. A further step is applying stretching exercises. A certain level of force plays an important part in the process of flexibility development. It is important for achieving limits in an active way. It is also as important to maintain muscle balance. In some sports disciplines, one-sided load prevails (tennis, volleyball, floorball), which may lead to violating balance. Muscle imbalance appears when there is imbalance between agonists and antagonists. As a rule, one of the muscles is shortened and the other one weakened. An example of this can be the shortening of pectoral muscles and weakening of scapula muscles in volleyball players. As a consequence, shoulders move forward, which causes insufficient movement range at reception outside body axis in volleyball. Another example of muscle imbalance appears in pair limbs in tennis players when the joint range (e.g. in external shoulder rotation) is bigger in the strike arm. A complex training of flexibility includes joint range development, strengthening agonists and antagonists and eliminating muscle imbalance. This process uses the combinations of:

• Relaxation exercises
• Stretching exercises
• Strengthening exercises

Relaxation exercises

The aim of relaxation exercises is to decrease the tension in the muscle before it is subsequently stretched. The basis is movements in individual segments of the body such as flickering, shaking, swinging or rotating with an emphasis on decreasing tension as much as possible. A suitable position for performing relaxation exercises is lying on the back or side, often with the help of a partner. Individual movements are performed in 15-30 repetitions. The aim of relaxation exercises is decreased tension in skeletal muscle before its stretching.

Stretching exercises

Stretching is a name of the process of controlled stretching of skeletal muscles and ligament structures. Three basic stretching techniques can be distinguished:

• Static
• Dynamic
• Proprioreceptive stretching

Static stretching represents a method of slow, intentional muscle stretching, which means stretching the muscle to the limit position and maintain it. Muscles must be warm, well perfused and relaxed. An example of this can be static hamstring stretching.

There are 3 stages:

• initial mild stretching up to a light tension (a warm feeling in muscle tissue, no pain), hold for 10-30 s
• developing stretching which follows after 2-3s relaxation at the end of the preceding stage, the aim is to further increase movement range; it must be performed following the same criteria the preceding stage (hold for 10-30s)
• drastic stretching which is accompanied by unremitting pain in the muscle. There is a risk of a damage to the muscle
• the exercise can be repeated up to 3 times

This method is considered very saving and safe. The main advantages include:

• it is easy to learn
• it provides enough time to “shift” the limit of activating stretch reflex
• it does not require much energy investment
• with training of sufficient intensity, it can cause muscle relaxation through impulses from Golgi tendon bodies

Dynamic stretching uses motor energy of the parts of the body to multiple fast or short muscle contraction which is stopped in limit position. Multiple repetitions (15-30 times).

Proprioreceptive stretching

One of the methods presents stretching the muscle after its preceding contract-relax.

Basis: muscle tension increased with resistance enables subsequent bigger passive stretching.

Procedure:

• the muscle is stretched passively below pain limit
• in this position, static contraction against external resistance is performed (4-6 s)
• relaxation after resistance (relaxation) – infaltion – exhalation (2-3 s)
• passive stretching to limit positions (10-30 s)

The effect of stretching

• “Shifting” the critical point for activating stretch reflex.
• Regular and long-term stretching leads to an increase in the number of sarcomeres.
• Regular and long-term stretching leads to a change in the length of ligaments surrounds muscles (epimysium, endomysium, perimysium).

Basic principles of flexibility development

• Warm-up and stretch properly.
• Combine relaxation, stretching and strengthening exercises with the weight of one’s own body.
• Perform stretching slowly up to the point of feeling slight tension.
• Never exceed pain threshold.
• Not always is it possible to reach maximum position.
• Concentrate on stretched area and do not forget about regular breathing.
• Stretch less flexible part of the body first.
• In static exercises, hold in limit positions up to 60 seconds.
• A complex of 8-12 exercises for different joints within one training block.
• Stretch back less intensively but more frequently.