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1. Definition of flexibility and injury

    Flexibility can be defined as the amount of movement of a joint through its normal plane of motion. But we can differentiate between static and dynamic flexibility. The static is defined as the range of motion available to a joint or series of joints. The dynamic flexibility refers to the ease of movement within the obtainable range of motion. (Gleim, GW and McHugh, MP. 1997).

    There are lot of different definitions of injury, but the most important thing is that the definition be clearly explained and understandable. Soft tissue injuries are hard to classify and quantify, so various attempts have been made to define a sport injury: new symptom, decreased function or decreased performance, inability to participate in sport, medical consultation, absent from work, self diagnosis. (Leatt, P. 1998).

2. Epidemiological studies on flexibility and injuries

    Most of the studies on flexibility and injuries agree that there is a relationship between both factors. But there are another studies where the results demonstrate that the flexibility do not have a clear influence on the sport injuries. What happen is that the sport injuries don't depend only of the flexibility, there are lot of other risk factors that have an influence, like the psychological, physiological or environmental factors.

2.1 Studies on flexibility and injuries

    William E. Garret, in his article about the muscle strain injuries, expose that among the factors felt to be important in the behaviour of muscle and the prevention of injury are innate flexibility, warm-up, and stretching before exercise. Usually the response of muscle to stretching has been explained on a neurophysiological basis with reference to stretch reflexes. However, many properties of muscle in response to stress might be explained with reference to viscoelastic properties common to connective tissue in general. (Garret, WE. 1990).

    The hamstrains strains have been studied in different researches. One of them was the Liemohn´ study, whose conclusions were that the non-injured groups always tended to be more flexible than the injured groups; furthermore a greater degree of bilaterality was also noted in the non-injured groups relative to flexibility. The data of his study did not show that the least flexible limb was the one that was usually injured. (Liemohn, W. 1978).

    Studies suggested that musculoskeletal tightness in football players may be associated with an increased likelihood of muscle strain injury. Subsequently, retrospective studies have shown that athletes with previous hamstring strains have limited flexibility and prospective investigations have suggested that lower extremity tightness predisposes to injury. It is commonly implied that the relationship of skeletal muscle flexibility to injury is in part related to the passive properties of the muscle. It was recently suggested that acute and long term increases in maximal attainable joint range of motion is related to the subject's tolerance to the stretch, rather than the passive properties of the muscle. However, it remains unclear if subjects with varying flexibility have a different tolerance to stretch. (Magnusson SP. Et al. 1997).

    Recognition of the muscle injury may be based on the four general categories of clinical presentation. They are: acute injury, chronic injury, acute exacerbation of a chronic injury, and subclinical functional alteration.

    Complete and accurate diagnosis of the injury can be established by identifying which of the five components of the muscle injury complex are present in each injury. In each muscle injury, there are five separate areas that may be identified as contributing to the production or continuation of symptoms. These components have an effect on either muscle anatomy or muscle functions. They are tissue injury complex (that area of actual anatomical disruption), clinical symptom complex (that group of symptoms which are causing acute pain, swelling, and dysfunction), functional biomechanical deficit (that combination of muscle inflexibilities, weakness, and imbalance which cause inefficient mechanics in performance of athletic activity), functional adaptation complex (that set of functional substitutions the athlete employs as a result of the injury in order to maintain performance), and tissue overload complex (that group of tissues that may be subject to tensile or eccentric overloads that may cause or continue symptoms or disability.

    These components are actually parts of a negative feedback loop, or vicious cycle, that is operative in muscle and muscle overload injuries. Depending on an athlete's intensity or duration of continued use, cycling within this loop may continue for varied periods of time before actual clinical symptoms are manifest. During this time, the athlete's total function may be fairly normal, but its efficiency may not be as optimal as it should. A thorough evaluation of each athlete with respect to inflexibilities, weaknesses, or imbalances will demonstrate the deficits and allow the diagnostic and therapeutic process to begin. (Kibler, W.B. 1990).

    For the purposes of Magnusson´ study flexibility was defined as normal or tight based on a toe-touch test. Subjects were requested to reach as far down as possible with both hands while standing on a stool with their knees completely extended without any warm-up or prior trials. The distance (cm) between the level of the stool and the finger tips was recorded with a tape measure. Subjects were defined as normal (n=8) if they were able to reach the level of the stool (0 cm) or beyond (indicated as positive values). Subjects were defined as tight (n=10) if they were unable to reach 10 cm or closer to the level of the stool (indicated as negative values).

    The results of the study specifically tested the subjects' tolerance to the stretch by bringing the leg to the onset of pain. Tight subjects had a lower stretch tolerance, as indicated by the lower maximal angle, torque, stiffness and energy. That is, tight subjects experience pain at a lower angle and tension than subjects with normal flexibility. The structures responsible for stretch tolerance are unknown.

    So, the discussion of the study was that restricted flexibility may be related to the mechanism of muscle injury. It is believed that the passive properties of the muscle are of importance in this respect. (Magnusson SP. Et al. 1997).

2.2 Flexibility and injuries in football´s studies

    Most of the studies are based in football players, so we think that it´s important to do a special mention for this big group of sportspeople.

    Inklaar did a study about soccer injuries, the aetiology and prevention, and he said that poor flexibility or muscle tightness has been identified as a risk factor in soccer. He studied senior amateur soccer players, who in general were less flexible than a group of age-matched nonplayers. In soccer players, more muscle tightness was measures in hip abduction, hip extension, knee flexion and ankle dorsiflexion. The 67% of the soccer players were found to have one or more tight muscles in the lower extremity.

    In elite senior soccer players in Belgium, 39% of the strains were re-injuries of the same type and location. A correlation between muscle tightness and strains of the adductors and tight muscles was found. The cause of muscle tightness in senior soccer players is not yet known. Muscle tightness may be the result of the high demands soccer puts on the muscle strength and power and the poor attention that is generally paid to flexibility training. Also, muscle tightness may be the result of former muscle injuries. The finding that few muscle and groin problems exist in youth soccer players probably can be explained by a greater flexibility among the youth players. (Inklaar, H. 1994).

    If we talk about injuries in football players we have to talk about Jan Ekstrand and Jan Gillquist, who did lot of different studies about this subject, especially about the muscle tightness and injuries. In two different studies with one hundred-eighty players in a male, senior soccer division were examined for past injuries, persisting symptoms from past injuries, and muscular tightness in the lower extremities.

    Soccer players were in general less flexible than a group of nonplayers of the same age. No correlation was found between past injuries and existing muscle tightness.

    No differences could be found between players with injuries to the lower extremity during the previous year and the rest. Strains had occurred in 31% of the players with muscle tightness but in only 18% of the players with normal flexibility.

    The final conclusion was that the cause of muscle tightness in soccer players seems to be associated with training methods. It has been suggested that stretching and other flexibility exercises will improve performance and prevent injury. (Ekstrand, J. Et al. 1982 and 1983).

2.3 Flexibility and injuries in young athletes

    A large group of sports practicants are the adolescents, where probably the largest group of adolescents with overuse injuries are those who have developed their symptoms and condition as a result of the effects of the normal growth process. During phases of rapid bone growth, such as the adolescents growth spurt, this creates tightness and inflexibility across the joints as the lengthening of the musculotendinous unit lags behind that of the bone itself. This inflexibility creates imbalances across the joints, and during sports or play activity increased stresses are applied to both the joints and the attachments of the musculotendinous units themselves. (Dalton, S.E. 1992)

    Most of the injuries like coxa vara or valgus deformities of the knee, foot or ankle, excessive foot pronation, chondromalacia, etc; settle with a reduction in stress applied, restoration of muscle flexibility and the slowing of the growth process. Preparticipation evaluation of adolescent athletes is a risk due to alignment disorders and poor flexibility and plays a major role in the prevention of injury, so muscle flexibility is a risk factor in overuse injuries.

    A Bruce H.Johns et al. study about epidemiology of injuries associated with physical training among young men in the army was conducted to assess the incidence, types, and risk factors for training-related injuries among young men undergoing Army infantry basic training. Subjects were followed over 12 weeks of training.

    The data indicate that both the most flexible and least flexible individuals are at higher risk of lower body injuries. It has been suggested that athletes with tight muscles (low flexibility) are more susceptible to muscle strains, whereas those with ligamentous laxity (greater flexibility) are predisposed to a higher risk of sprains and dislocations. Whatever the underlying reason, the finding that both extremes of flexibility experience more injuries, and its implications for the prevention and rehabilitation of injuries deserves further study. (Johns, B.H. 1993).

    In a J.Knapik, B. Jones, C.Bauman and J.Harris´ study the results coincide with the previous study results, where the low and greater flexibility are predisposed to a higher risk of injuries. Subjects in the least flexible and most flexible quintiles were, respectively, 2.5 and 2.2 times more likely to get injured than subjects in the middle quintile. (Knapik, J.J. Et al. 1992).

    Another study of the same group of researchers was about athletic injuries in female collegiate athletes.

    One hundred thirty-eight female collegiate athletes, participating in eight weightbearing varsity sports, were administrated preseason strength and flexibility tests and followed for injuries during their sports season. Flexibility was measured as the active range of motion of several lower body joints.

    The study demonstrated that specific strength and flexibility imbalances were associated with the first incidence of a lower extremity injury in female collegiate athletes. Athletes whose hip extensors had a 15% greater range of motion on the right side were 2.6 times more likely to get injured than athletes with less than a 15% imbalance. It seemed reasonable to expect that a hip extensor flexibility imbalance on either side of the body may predispose the athlete to injury.

2.4 Contradictions on flexibility and injuries

    Up till now we only have talked about the studies where the results show that there are a relationship between flexibility and injuries, but there are another studies where the results show the opposite.

    The purpose of S.Messier and K.Pittala´ study was to determine whether a relationship exists between selected biomechanical, anthropomentric, and training variables and runners afflicted with one of the following three injuries: iliotibial (IT) band friction syndrome, shin splints, and plantar fasciitis.

    The most apparent factor was that 53% of the plantar fasciitis group had a leg length difference of at least 0.64 cm compared to only 21% of the control group. Poor lower back and posterior thigh flexibility have been implicated as etiologic factors in the development of running injuries. The absence of significant differences in flexibility measures may be due, in part, to the insensitivity of the tests. The important point here, however, is that it appears the magnitude of the differences in lower back and hamstring flexibility between injured and non-injured runners is small. (Messier, SP. and Pittala, KA. 1988).

    In a study of L. Hennessy and A.Watson the posture and flexibility were assessed in 34 athletes. Subjects were divided into two groups: a noninjured group that did not have a history of hamstring strain injury within the previous 12 months; an injured group that had a history of hamstring strain within the previous 12 months. Ten different postural components were assessed. Hamstring flexibility was assessed in both legs.

    The results of the study indicate that while differences in hamstring flexibility are not evident between injured and noninjured groups poorer low back posture was found in the injured group. (Hennessy, L. and Watson, AWS. 1993).

    This in agreement with the findings of Stephens and Reid. In their study the authors found no difference in flexibility as determined by the sit and reach test between football players with a history of hamstring injury and players who did not experience hamstring strains.

    Using a mixed longitudinal design, the incidence of injuries, and the development of flexibility and isometric strength of the upper and lower limbs were studied for two years in 453 elite young athletes by N. Mafulli, J. King and P. Helms. Strength and flexibility did not exert a significant role in determining injuries. The rate of injury was not significantly different between the two years of the study.

    The present study suggests that some ranges of motion are sports specific, and the most of them are influenced by age.

3. Conclusions

    After see the different results of the researches about the relationship between flexibility and injuries we only can say that we do not know yet the real existence relation. There are enough studies that demonstrate the benefits of a good flexibility in sportspeople, but the biggest problem is that the injuries are produced for lot of different factors, and flexibility is only one of them, and we do not know yet the importance rank of the flexibility. It´s very difficult separate the flexibility risk factor from the others risk factors that are involved in sports injuries.

    Finally, we want to promote flexibility exercises in every warm-up and after physical activity to prevent injuries.

References

• Dalton, S.E. Overuse injuries in adolescents athletes. Sports Medicine 13 (1): 58-70, 1992.

• Ekstrand, J. and Gillquist, J. The frequency of muscle tightness and injuries in soccer players. The American Journal of Sports Medicine, vol. 10, No. 2, 75-78. 1982.

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• Ekstrand, J. and Gillquist, J. Prevention of Sport Injuries in Football Players. International Journal of Sports Medicine, vol. 5, 140-144 Supplement, 1984.

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• Kibler, W.B. Clinical aspects of muscle injury. Medicine and Science in Sports and Exercise. 22, 450-452. 1990.

• Knapik, J.J.; Bauman, C.L.; Jones, B.H.; Harris, J.M.; Vaughan, L. Preseason strength and flexibility imbalances associated with athletic injuries in female collegiate athletes. American Journal of Sports Medicine, vol. 19 (1), 76-81, 1991.

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• Leatt, P. Notes from Sports Medicine and Rehabilitation´s module (not edited). Liverpool John Moores University. 1998.

• Liemohn, W. Factors related to hamstring strains. Journal of Sports Medicine and Physical Fitness, vol. 18; 71-76; 1978.

• Mafulli, N.; King, J.B.; Helms, P. Training in elite young athletes (the training of young athletes (TOYA) study: injuries, flexibility and isometric strength. British Journal of Sports Medicine 1994; 28 (2); 123-136

• Magnusson SP, Simonsen EB, Aagaard P, Boesen J, Johannsen F, Kjaer M. Determinants of musculoskeletal flexibility: viscoelastic properties, cross-sectional area, EMG and stretch tolerance. Scandinavian Journal of Medicine & Science in Sports 1997: 195-202.

• Messier, S.P. and Pittala, K.A. Etiologic factors associated with selected running injuries. Medicine and Science in Sports and Exercise 20 (5), 501-505. 1988.

• Reid, D.C.; Burnham, R.S.; Saboe, L.A.; Kushner, S.F. Lower extremity flexibility patterns in classical ballet dancers and their correlation to lateral hip and knee injuries. American Journal of Sports Medicine, vol. 15 (4), 347-352, 1987.

• Schmidt-Olsen, S.; Jorgensen, U.; Kaalund, S.; Sorensen, J. Injuries among young soccer players. American Journal of Sports Medicine, vol. 19 (3), 273-275, 1991.

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