Hawkins et al., (2001) suggested that muscular strains are the single most commonly reported injuries in English professional soccer. This data is consistent with previous research, which reported similar findings (Hawkins and Fuller, 1999; Lewin, 1989; Ekstrand and Gillquist, 1983a, 1983b). This epidemiological research (studies of the incidence of injury) sought to identify the causes of occupational injury in professional soccer players and served as the exploratory level of research on the nature of soccer injuries. Further research has attempted to investigate the relationship between extrinsic and intrinsic factors and the incidence of muscular injury, particularly hamstring muscle injury (Orchard et al., 1997; Orchard 2001).
Various factors have been implicated in the cause of hamstring injury, including adverse neural tension (Turl and George, 1998), fatigue (Roberts and Smith, 1989; Mair et al., 1996), lack of muscular strength (Worrell and Perrin, 1992), muscular imbalances (Bennell et al., 1998), previous injury (Taylor et al., 1993; Orchard, 2001), and a lack of muscular extensibility (Ekstrand and Gillquist, 1983a, 1983b). Further research by Keller et al (1987) felt that “tightness” or “stiffness” was a major causative factor for muscle injury. Ekstrand and Gillquist (1983a, 1983b) advocated stretching as a strategy to reduce hamstring muscle injuries by increasing extensibility.
Based on these recommendations, stretching techniques have been developed in the training and rehabilitation of elite level soccer players at both youth and senior level (Ekstrand and Gillquist, 1983a Safran et al. 1989). Stretching is intended to improve range of motion (ROM), prevent injury and reduce muscle soreness after physical activity (Van Mechelen et al., 1993; Safran et al., 1989). Stretching for the above goals has become a paradigm within professional soccer which, once established, has become almost ritualistic – as demonstrated before every Premiership match in England. In common with other training practices in professional soccer, the adoption of stretching has occurred despite a lack of sound physiological or scientific evidence to support its use as an injury prevention strategy (Reilly et al. 1993). Some authors have questioned the efficacy of stretching as an injury prevention strategy, as much of the evidence supporting its use remains empirical (Smith, 1994).
Ekstrand and Gillquist (1983a) undertook a prospective study of 180 amateur football players to illustrate the incidence of injury during the year. The authors found that 88% of injuries involved the lower extremities and that muscle strains accounted for 48% of all injuries. This led the authors to advocate a lower limb stretching and strengthening regime as a strategy to reduce the incidence of these injuries, these suggestions being based on conventional theories that have only face validity (i.e. it seems logical), rather than being backed by strong scientific evidence. Methodological issues reduced the clinical value of Ekstrand and Gillquist’s (1983a) research. The authors provide a confusing definition of injury, where return to practice is the main criteria used to define the severity of injury – but this may be related to other factors such as the player for some personal reason not wanting to return to practice, or differences in the management of the injury, rather than the severity of the injury. The study incorporated ten teams in total and each team coach selected 15 players to take part. The authors do not state the selection criteria used by the coaches, and this may affect the outcome. Although the same orthopaedic consultant examined all the injuries, the data was recorded retrospectively and therefore not all the information may have been recalled. In research terms this can be classified as systematic error (Batterham and George, 2000).
Ekstrand and Gillquist (1983a) concluded that “muscle tightness” represented by decreased range of motion was a prominent characteristic in players who later developed injury. Range of motion and muscle strength in the lower extremities were measured in a pre-season test. According to Ekstrand and Gillquist’s (1983a) classification, 63% of players had tight muscles. The soccer players were less flexible than the reference group concerning hip abduction, hip extension, knee flexion, and ankle dorsifiexion. The authors somewhat overstate their findings by inferring cause and effect; this is not valid in a correlational study of this type. Also the definition of muscular “tightness” used by Ekstrand and Gillquist (1983a) could be said to lack construct validity, as the authors only examined range of motion and there was no direct attempt to measure muscle tightness. Even using an indirect method, the authors found no significant difference in the hip joint range of motion of players who had hamstring strains and the players who had not suffered such injuries. Presumably this is because the aetiology of hamstring strain is due to a cumulation of variables (Garrett, 1996; Orchard, 2001).
Hennessy and Watson (1993) assessed posture and flexibility in athletes, with the subjects divided into two groups. The first group was a non-injured group that did not have a history of hamstring strain, and the second an injured group that had a history of hamstring strain within the previous 2 months. Hamstring flexibility was assessed in both legs. The authors found no statistically significant difference in the flexibility between limbs for both the injured and non-injured group.
To summarise, there is mixed evidence from research investigating the relationship between decreased hamstring extensibility and hamstring muscle injury. Where previous authors (Ekstrand and Gillquist, 1983; Keller, 1987) were quite unequivocal that there was a strong relationship between decreased extensibility and muscle injury – to the point where they felt it was the major aetiological factor – more recent research supports a multi-factoral aetiology of hamstring muscle strains.
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