THE CONCEPT OF FLEXIBILITY
Flexibility, mobility and suppleness tend to signify the same fundamental faculty. Each denotes amplitude of joint movement and absence of stiffness. The vocabulary is further extended when calisthenics, mobilising or stretching exercises describe training procedures. Two attributes have been distinguished – extent (or static) and dynamic flexibility (Fleishman, 1964). Extent flexibility refers to the range of movement possible at a particular joint or series of joints in functional combination. Dynamic flexibility describes the ability to move part or parts of the body quickly or make rapid and repeated movements involving muscle flexibility. The concern is with stiffness or the forces opposing movement over any range rather than the magnitude of the motion. It is manifested in such actions as squat-thrusts and is likely to be important in speed and power events.
It is misleading to regard extent flexibility as a general factor since it is largely joint specific (Harris, 1969). Good flexibility in a particular joint does not guarantee better than average values elsewhere. Different sport events have specialised forms of action that in turn produce particular changes in the range of motion so that specific patterns of flexibility are found in selected sports. Hurdlers and karate competitors, for example, need great hip abduction while gymnasts and soccer goalkeepers need good lateral flexion of the spine. Javelin throwers and shot putters tend to have outstanding wrist flexibility, while tennis players are mobile in the shoulder. Weightlifters excel in trunk, gymnasts in hip and swimmers in ankle extent flexibility, reflecting particular requirements for those sports (Leighton, 1957a; 1957b).
Dynamic flexibility has been called ‘agility that does not involve running’ (McCloy and Young, 1954). It is clearly distinct from agility which is defined as the ability to change direction of the body or its parts rapidly and is usually measured by standardised run tests (Cureton, 1970). Agility depends on a number of underlying abilities such as muscular power, reaction time, coordination, dynamic flexibility and at least a normal amount of extent flexibility. Agility can be paramount in avoiding hazards that present themselves without warning in field games especially.
Flexibility exercises are used in warming-up for training and competition and for more permanent effects as a component of the training programme. Justification for their practice is based on a number of counts.
Firstly, suppling exercises are employed in warming-up as a precaution against injury in the more strenuous exercise to follow.. There is an immediate beneficial effect on flexibility so that muscles are less tight when competition starts (Atha and Wheatley, 1976a). Consequently they are better able to survive a sudden stretch intact. Performance is also likely to be assisted by the elevation in muscle temperature produced. Though there is no conclusive evidence that preliminary flexibility exercises substantially reduce the risk of injury, their practice is uniformly supported as sound by practitioners. Muscle soreness from succeeding activity is known to be reduced (De Vries, 1959), and stretching exercises the day after strenuous competition help to ameliorate sore muscles (De Vries, 1961; 1962).
Secondly, improvement in extent flexibility is likely to assist performance by allowing a more efficient posture to be assumed. The butterfly swimmer, for example, can more easily get into a flat streamlined position and still recover his arms over water. Increased flexibility in specific regions is likely to improve technique in hurdling, diving, gymnastics and ballet, all of which require extremes of particular movements. Greater flexibility also allows application of force over a wider distance. Increased hyperexten-sion of the shoulder permits the javelin thrower to exert force on the implement over a longer distance before release. This should increase the acceleration and assist the throw.
Thirdly, improved flexibility reduces the susceptibility to injury since the joint has greater margin to yield under strain. Liemohn (1978) presented evidence that inflexibility in the hip predisposes towards hamstring strains. Alternatively, hypermobility can be disadvantageous in that the individual may adopt extreme positions where the joint is unstable and unable to withstand the mechanical strain imposed on it. For this reason extreme flexibility measures have been proposed as a screening tool for contact sports (Mathews and Fox, 1976).
Finally, adaptive shortening of connective tissue resulting from inactivity and resisting movement can be reversed by flexibility routines. Though extremes of flexibility are of little value in normal activity, inactive individuals tend to be inflexible (McCue, 1953) and lack adequate range of motion for many day-to-day activities. Attention to restoring extensibility applies to athletes returning to training after enforced inaction through injury as well as to the habitually sedentary embarking on an exercise regimen.
THE MEASUREMENT OF FLEXIBILITY A variety of instruments have been devised for measurement of flexibility and procedures standardised for extent flexibility measurement (Billig and Loewendahl, 1949; Cureton, 1947).
The goniometer consists of a 180° protractor constructed of plexiglass, wood or stainless steel. It may have two extended arms, one fixed at the zero line and one mobile, or just one mobile arm which can be locked in any position . The centre point of the protractor is aligned with the centre of the joint being measured and readings taken in extreme flexion and extension.
The flexometer designed by Leigh ton (1955) overcomes the disadvantage of the goniometer in that no decision is required as to what constitutes the axis of a bony lever. The device contains a rotating circular dial marked off in degrees and a pointer counter-balanced to ensure it always points vertically . It is strapped on to the appropriate body segment and the range of motion determined in respect to this perpendicular.
The universal clectrogoniometer designed by Kar-povich and Karpovich (1959) consists of two brass shafts attached to the knob and housing of a potentiometer. The shafts are secured by snap fasteners to a chassis strapped to a body segment, the length of the chassis and shafts depending on the joint studied. Displacement and velocity are continuously recorded during motion so that changes in joint angles throughout a movement are monitored. According to Adrian (1973) over a dozen types of elgons have been designed since the original. Currently miniature potentiometers and lightweight plastics are employed so movement is not inhibited and concomitant emg analysis permitted.
Photographic techniques reported by Hunnebelle et al (1972) are useful for measuring flexibility in body segments difficult to stabilise, notably the hips and trunk.
Maximal flexion and extension movements are held for one to two seconds while photographs are taken. Amplitude of each movement is determined from the photographs after drawing the direction of the body segments and measurement of appropriate angles.
Flexibility has been measured with different forms of a general test incorporating hip and back flexion. Three practical tests are more commonly used.
SCOTT AND FRENCH (1950) BOBBING TEST A 20 inch (50cm) scale marked in half-inch (1cm) units is attached to a stable bench, the middle of the scale being level with the bench top. Standing with toes even with the front edge of the bench, the subject bobs downwards forcefully four times reaching equally with fingers of both hands while keeping the knees fully extended. The score is the lowest point reached in the series or attained and held for two to three seconds. This test has been modified for non-athletes to permit mild knee flexion and requires slow rather than bobbing movements to avoid possible hamstring strain (Reilly, 1971).
KRAUS AND HIRSCHLAND (1954) FLOOR-TOUCH TEST This consists of attempting to touch the floor from standing, keeping the knees extended and holding the end position for three seconds. The test originated in a posture clinic for treatment of patients with low back pain as it was maintained that a certain degree of flexibility in the back and hamstrings is essential for preventing low back disorders. It was included with five other items in a battery of minimum muscular fitness tests which have been extensively applied to children, the flexibility test typically producing the highest failure rate.
WELLS AND DILLON (1952) SIT AND REACH TEST The subject assumes a long-sitting position and slides both hands forward on a suitably placed low table as far as possible. A marked scale is incorporated on the table with the zero line directly over his feet which in turn are firmly pressed against a cross-board. The score is the distance reached by the finger-tips.
Methods have been designed to measure the torque needed to move a joint through various ranges of motion at varying speeds (Wright and Johns, 1960). The apparatus of Goddard et al (1969), for measuring the passive resistance of the human knee joint to an applied force, used a strain gauge torque plate and an angular displacement transducer. The contribution of a simple frictional component proportional to the normal force between the joint surfaces, a viscous component due to the shear of the synovial fluid film between the articulating surfaces as well as an elastic component can be extracted. Results can be expressed in dissipative stiffness, representing the resistive torque exerted by the articular surfaces and their lubrication, and elastic stiffness due to the soft tissue around the joint. Arthrography has, as yet, been applied more to study diseased conditions such as rheumatoid arthritis and osteoarthrosis than to physical performance.
LIMITATIONS TO MOVEMENT
Limitations to movement vary with the type of joint and the soft tissue around it. Hinge joints for example may be limited in the extreme position by adjacent bony surfaces as occur in elbow and knee extension. This factor is unlikely to alter once epiphyseal growth plates have closed. The long bones are especially more pliable during growth and hence their joints can be affected by hard training in the developmental years. Ballet dancers as well as gymnasts commence training at an early age and have a significantly higher incidence of hypermobility in many joints (Grahame, 1971). Extreme hypermobility may be due to osteogenesis imperfecta (McKusick, 1966) or to intense training prior to calcification of the growth plates . Inextensibility of soft tissue may be the factor limiting movement as occurs in shoulder or hip flexion and extension at the ankle joint. By far the greater flexibility in flexion and extension is found in the shoulder joint being approximately 260° compared with 65° at the ankle and hip or 75° at the trunk in normal individuals (Leighton, 1957a; 1957b). The greater flexibility is at the expense of stability and arises from the shallow insertion of the humeral head into the glenoid cavity, security being attained by the surrounding ligaments and muscles. Lax ligaments may in some cases cause hypermobility and can be due to pathological conditions whereas excessively tight ligaments may restrict limbs from moving to extreme positions. Prevalence of ligamentous laxity due to a process of natural selection and heredity has been put forward to partially account for the hypermobility in ballet students (Grahame and Jenkins, 1972). The restraint on movement imposed by ligaments may at many points be reinforced by muscular tension which may actually check movement before the ligaments are fully stretched. This effect is called passive insufficiency or the ligamentous action of muscle. Tension in the hamstrings, for example, while the knee is fully extended, limits hip flexion.
Dynamic flexibility may be restricted by the resistance of soft tissue. Data obtained by Johns and Wright (1962) indicate that the largest contribution to stiffness in the mid-range of free movement is from the joint capsule (47 per cent), secondly muscles and their fascial sheaths (41 per cent) and thirdly tendon (10 per cent), while skin contributes minimally (2 per cent). At extremes of motion, tendons have a more limiting effect while excess subcutaneous fat deposits may impede mobility particularly in the hip/trunk region. Hypertrophied muscle, as could occur with highly developed biceps, deltoid or hamstrings, might impair flexibility. The contractile elements of muscle comprising the acto-myosin complex are mainly affected by strength training while the elastic components, consisting of the fascia and connective tissue surrounding the fibres and to some extent the Z discs linking successive sarcomeres, are provoked in stretching exercises. Consequently it is recommended that muscle extensibility should not be neglected when intensive strength training programmes are followed.
Movement may also be limited by neuromuscular factors. As actions proceed, sensory information about movement and limb positions is provided by proprioception. The muscle spindle is activated when a muscle is passively stretched and evokes reflex contraction in the muscle being stretched. This is called the myotatic or stretch reflex. It serves to facilitate the contraction of the muscle stretched but has also a protective function in securing appropriate postural adjustments or withdrawal from extreme positions. Golgi tendon organs, found mainly in musculotendon-ous junctions, are deformed whether the muscle is shortening or being stretched. This effect is inhibitory and functions to protect the entire operating muscle group by damping moto-neuronal discharges. Pacinian corpuscles, located in joints and in sheaths of muscle and tendon, sense pressure and along with the free nerve endings are involved in pain tolerance at extreme positions. The condition of peripheral nerve trunks may also limit movement. Hip flexion, for example, may be limited by irritability of the sciatic nerve as well as tight hamstrings.
Flexibility seems to be independent of physique (Laubach and McConville, 1966) and largely unrelated to anthropometric variations (Mathews et al, 1957). Only extremely disproportionate body builds were found by Broer and Galles (1958) to have any advantage in a toe touch test. There is a circadian variation in joint stiffness with lowest levels in the morning and late evening (Wright et al, 1969). Since stiffness increases with decreased temperature the proximity of the curve to the circadian rhythm of body temperature is not surprising. A similar circadian variation has been found for hip/trunk flexibility (Stockton et al, 1978). Preliminary stretching exercises are especially advisable for those athletes engaged in early morning training.
It is well established that girls of most ages have greater hip/trunk flexibility than boys (Phillips, 1955). It seems this superiority exists at all ages and persists through adult life. Boys lose flexibility as they enter adolescence from 10 to 12 years of age, then improve until late teens without regaining the early childhood levels. Girls increase in flexibility from 6 to 12 years of age and then gradually deteriorate (Hupprich and Sigerseth, 1950).
In normal individuals, dynamic flexibility appears to grow steadily poorer from childhood onwards though this is largely due to low habitual activity levels rather than an innate early ageing effect.
TRAINING FLEXIBILITY Training effects
Training effects on flexibility are observed within a single session as a warm-up result and this persists for more than one day (Atha and Wheatley, 1976a). Persistent effects are found after three to four weeks of regular training and may be attributable to various causes.
Firstly, structural changes in the mechanical realignment of the network of tissues crossing the joint or lengthening of semi-plastic elements in those tissues may occur. This results from moving a joint beyond the normal end position to the point of real discomfort. The principle is that the rate of increase of flexibility depends on the magnitude of the imposed stretch.
Secondly, greater relaxation is found in the antagonist which permits further movement without producing tension to oppose it. This is achieved by prop- rioceptive neuromuscular facilitation. Increased flexibility follows the reflex inhibition of muscles resisting movement in the limiting position.
Thirdly, tolerance to pain induced by maximum stretching of the tissues crossing the joint improves. Alterations occur in receptor bias which change the strength of the stimulus needed to exceed the pain threshold of a limiting position.
Overload to which restricting tissues adapt is presented by stretching them to the point of discomfort. If this stimulus is discarded the training effect reverses as the joint gradually loses flexibility. It is important to maintain flexibility exercises in training routines through the competitive season. The exercises should be conducted before exhausting strength or endurance training so that they can more easily be executed properly. Stretching exercises are particularly important for injured muscle as scar tissue forms so that repair in a shortened position must be avoided. During recovery, exercises can be worked out which contract the antagonist to the injured muscle which is itself stretched in consequence.
In active flexibility movement is carried to the end position. An example is lateral flexion of the spine performed while standing where the trunk is bent as far as possible alternately to left and right sides. Movements may be carried out slowly or in a jerking ballistic action. Both methods achieve similar results, the slow stretching being preferable for its reduced injury risk as pain can be felt before any tissue damage occurs. Active exercises are suitable in a general warm-up where all major joint complexes can be systematically mobilised. A sound strategy is to start with neck rotation and progress downwards to end with ankle exercises.
In static stretching the limiting position is actively held for a period or body segments to be extended are locked in position at their greatest possible range. This is exemplified in the achievement of certain positions in Hatha Yoga postures .
In passive exercises the limb is moved to its end position and held there by external resistance. This method can be useful to the physiotherapist in restoring normal joint function to an injured limb. It must be applied cautiously even by experienced coaches and it is essential that the athlete relaxes completely during the exercises. The theoretical advantage of this technique is that the normal limb rebound in active exercises due to the stretch reflex is prevented. Passive flexibility work should be followed up by active exercises which allow the agonist to contract so that the increased flexibility is accompanied by increased strength to enhance stability in the newly acquired range. This passive lift to the limit can also be followed by a maximum isometric contraction for about six seconds against the manual resistance provided, and repeated five or six times.
PASSIVE MOBILISING METHODS Short-term improvements in flexibility have been found with heat treatment and cycloid vibration massage. Diathermy has long been known to allow greater mobility in stiff joints (Benson, 1930). Dynamic flexibility is improved 20 per cent by local warming of a joint to 45 °C and is decreased 10 to 20 per cent by cooling to 18 °C (De Vries, 1977). Local application for 15 minutes of cycloid vibration of low amplitude and frequency can be equally as effective as a programme of flexibility exercise of similar duration (Atha and Wheatley, 1976b). These changes occur as a result of improved muscle relaxation (Bierman, 1960). In practice exercise-induced flexibility is preferred because of its known long-term effects and additional concomitant benefits.
An almost endless number of exercises can be devised for flexibility. These will depend on the degrees of freedom of movement at the particular joint and the needs of the athlete. Particular sports call for their own special emphasis. Considerable variety can be achieved on any one exercise simply by changing posture. Lateral flexion of the spine can be conducted either by slowly reaching down the side of the leg on each side successively while standing, or from a supine position parting the legs, and attempting to touch the ankle first on the left then the right while keeping legs and shoulders in contact with the floor. A further example is the performance of hamstring stretching either by high kicks from a standing position or by raising one leg at a time from a supine posture. A selection of typical exercises for the major complexes of the body is now described.
Ballistic exercises include arm circling singly or together in as wide an arc as possible and repeatedly shaking hands behind the back with an imaginary person, the shoulder hyperextended. Elbows may be taken overhead and the fingers attempt to crawl down the back to the inferior angle of the scapulae. From a kneeling position with the back parallel to the ground, the hands supporting well in front, the armpits are forced towards the floor. Lying prone with the arms outstretched to form a cross, the arms are raised as high as possible.
Active exercises should include lateral flexion, rotation and twisting of the trunk as well as spinal flexion and extension. Trunk twisting can be combined with hamstring exercises in touching alternate toes with feet wide apart and knees extended from a standing or sitting position. Spinal flexion can be improved by attempting, from a sitting posture and legs outstretched in front, to bend forward and take the chin between both knees. Spinal extension can be performed while kneeling by pushing the hips forward and attempting to look overhead to see the floor directly behind. It can also be improved by holding an arch to crab position for 20 seconds or so, or with less flexible individuals holding an arch supported by the shoulders at the scapulae rather than the palmar surface of the hand. Another exercise is to repeatedly raise the legs, head and outstretched arms from a prone posture and hold this for about 15 seconds at a time.
A wide variety of exercises are possible because of the freedom of movement at this joint. Hamstring exercises should be counter-balanced by quadriceps stretching routines . A suitable advanced exercise for the hamstrings is to slowly move the feet forward from a press-up position until they are in line with the hands keeping the palms on the floor and the knees extended. Basic exercises involve attempting to touch the toes keeping the knees as straight as possible. With top athletes the leg may be retained for about 20 seconds in a high kick position by the experienced coach or at its end position when raised from supine for a similar period. With less flexible individuals it may be retained after a kick forward to rest on a chair top.
In most sports, considerable attention is needed to improve the ability to achieve a wide split between the legs in the sagittal and frontal planes. Long jumpers, decathletes, sprinters and fencers particularly need great fore-and-aft flexibility while outdoor games and racket players, gymnasts and combat sports competitors need great flexibility in the frontal plane to avoid adductor strains. Many athletes including hurdlers, skiers and gymnasts need both. Starting with the lotus position, appropriate split positions can be held while sitting. A lateral split can be facilitated by putting both feet against a wall while sitting, slowly moving the hips as close to the wall as possible by edging the feet further and further apart.
Flexibility training should be regarded as having an important role in the preparation of athletes for competition. It should help to reduce the risk of injury and facilitate optimum performance production. Special emphasis must be placed on the individual’s needs and bilateral flexibility development encouraged. Controlled active stretching is recommended for safety and good results. Passive manipulation at the limiting position should be conducted only with top athletes and under expert supervision. Communication between subject and partner helps to avoid any unnecessary strain. Stretching exercises are advised in the warm-up prior to competition and on the day following to eliminate stiffness.
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