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• Stretching and hamstring strains
  Ian Shrier
  Published on: 11 October 2022

• Published on: 11 October 2022

  Stretching and hamstring strains

  • Ian Shrier, physician, researcher

  Dear Editor,

  I recently read the article by Dadebo et al with interest [1]. I am a little confused by their results and their take home message. First, the correlation for SHT is reported as 0.02 (Table 6) and 0.54 (Table 8, one predictor) when the two correlations should be equal [2]. Second, the appropriate analysis is Poisson regression with counts of injuries as outcome and exposure rates as a covaria...

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  Dear Editor,

  I recently read the article by Dadebo et al with interest [1]. I am a little confused by their results and their take home message. First, the correlation for SHT is reported as 0.02 (Table 6) and 0.54 (Table 8, one predictor) when the two correlations should be equal [2]. Second, the appropriate analysis is Poisson regression with counts of injuries as outcome and exposure rates as a covariate. Third, the authors should report confidence intervals for the coefficients in the regression model for an appropriate interpretation. Fourth, if assumptions behind correlation and multiple regression statistics (e.g. linearity of relationship, non-correlated variables) are not valid, inappropriate interpretations are likely [2].

  Stepwise regression increases the complexity; forwards stepwise regression (adding variables one at a time) and backwards stepwise regression (deleting variables one at a time) usually produce different conclusions [2]. It is therefore very important to see the actual raw data in a figure for the univariate relationship [2]. For example, re-ordering the data of Table 5 shows that Division II had the least number of teams stretching and the lowest hamstring injury rate (Division II is more elite than Division III but still had lower injury rates). What was the actual risk of injury in teams that stretched and teams that did not (maybe produce 2 different categories for those that stretched different amount of times)?

  The correlations for warm-up and endurance training were higher than SHT and STE (Table 6, no correlation for strength training reported) but the injury rates were not reported. We need to know the coding for stretching technique to compare the three categories (add a fourth for “no stretching”). The analysis is a linear model and it is not clear why the authors suggest that stretching be limited to 15-30 seconds.

  Finally, the authors cite two studies suggesting stretching is associated with increased injury only in studies that used multiple interventions [3,4]. Neither study suggested this, and one [4] suggested the opposite; stretching was beneficial in a multi-intervention study [5], but the benefits were likely due to the other interventions.

  Given the previous research in this area, the current study design and lack of patient-level data, and the limitations noted above, it seems premature to recommend stretching to prevent injury in soccer players.

  References

  (1). Dadebo B, White J, George KP. A survey of flexibility training protocols and hamstring strains in professional football clubs in England. Br.J.Sports Med. 2004;38:388-94.

  (2). Glantz SA, Slinker BK. Primer of applied regression and analysis of variance. New York: McGraw-Hill Inc, 1990.

  (3). Gleim GW,.McHugh P. Flexibility and its effects on sports injury and performance. Sports Med 1997;24:289-99.

  (4). Shrier I. Stretching before exercise does not reduce the risk of local muscle injury: a critical review of the clinical and basic science literature. Clin.J.Sport Med. 1999;9:221-7.

  (5). Ekstrand J, Gillquist J, Moller M, Oberg B, Liljedahl S-O. Incidence of soccer injuries and their relation to training and team success. Am.J.Sports Med. 1983;11:63-7.

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  Conflict of Interest:
  None declared.

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