What is the evidence that poor flexibility is a risk factor for sports injury?

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Sports Medicine and Rehabilitation

What is the evidence that poor flexibility is a risk factor for sports injury?

Research into the area of physiological factors and their impact on injury incidence in sports has been considerable. It has become a priority to identify significant risk factors that are causing players and athletes to miss matches and sometimes a large slice of a season. With the increased numbers of games in a season and the increased standard of playing it is essential that an athlete is free from injury so that they can perform at their optimal level all of the time. Studies have been conducted so that the number of injuries can be analysed to show when they are happening, who too in particular and probably the most important why? The results can then be used to assess and ultimately prevent the risk factors and also measure the impact of an intervention programme that will reduce injury. This information can be of particular interest to sports companies who design protection such as shin pads and shoulder pads or to sports fitness instructors who can develop a regime that will rectify their problem.    

What is flexibility?

Flexibility is one of these physiological factors and has been described as the ability of skeletal muscle and tendon to lengthen (Gleim and McHugh 1997). There are two types of flexibility that can be measured for analysis. Static flexibility is the range of movement available to a joint or series of joints and dynamic flexibility is the ease of movement within that range of movement. These biomechanical factors and their relation to sports injuries stimulated considerable interest and extensive research has been conducted to try and explain these statements and to generate data that will provide meaningful evidence [1, 2, 4, 5, 6, 8, 9, 10, 12, 13].  

Evidence that poor flexibility is a risk factor.

        A recent study examined the relationship between increasing hamstring flexibility and the result it had on lower extremity overuse injuries (Hartig and Henderson 1999). Its strength was that is was conducted on approximately 300 military basic trainees who were all performing their 13 week training course at the same time. This is a strength because the environment is easy to control because they are all living in the same place and although the test was not compulsory the likelihood is that they were made to see the test through by their superiors. Consequently the follow up will be extremely good because the dropout percentage will be low. It will also mean that all the subjects will be doing the same infantry basic training course at the same time and so exposure to other variables can be controlled. These factors combine to ensure that the quality of the study will be excellent in that area.

        The design of the study looked at the effectiveness of implementing an intervention programme i.e. three hamstring stretching sessions that were incorporated into half of the military trainees existing fitness schedule. Throughout the 13-week training period any injury that the trainee occurred in the lower extremity was recorded by the troop medical clinic. This paper is also good because it does not give an absolute number of injuries but it states the incidence rate, which allows the data represented to be interpreted clearer i.e. the number of injuries compared to the number of training hours or trainees. Although the incidence is an important factor it is also important to find and record the severity of the injury. This is something that the researchers have failed to do and is a major weakness in this study. They have mentioned the types of injury that have occurred but have failed to show the number of each type in the total incidence rate. Therefore a sprained ankle could have been categorised the same as a torn ligament.

        The results of this study showed that both the control group and the intervention group both increased their flexibility but with a larger increase in the intervention group. This difference was found to be significant. When considering the incidence of injuries it was established that the number of lower extremity overuse injuries was significantly lower in the intervention group compared with the control group (Hartig and Henderson 1999).  Therefore this paper is excellent evidence that poor flexibility is an important risk factor in the development of a sports injury.

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        Another study that supports these findings was conducted on female collegiate athletes and investigated into flexibility imbalances and their association with athletic injuries (Knapik et al., 1991). The testing took place on 138 female subjects who participated in eight weightbearing varsity sports during their athletic season. The fact that it was during the season is a strength because it means that factors such as motivation would not have effected the results i.e. testing at the end of season when motivation levels are low and participant is not fully committed.  Selecting subjects from the same environment and subjects that were doing the ...

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