Research papers update

[injuryupdate]

Whilst the sports medicine journals continue to have plenty of output as usual, related articles seem to be finding their way more and more into the general medical press (in the same way that the lay press is increasingly fascinated by sports injuries). In last month's Medical Journal of Australia, there was an article (free full text) reviewing the rates of spinal injuries in rugby union and calling for greater injury surveillance.

http://www.mja.com.au/public/issues/181_01_050704/hay10067_fm.html

Unfortunately the Australian Federal government and opposition (despite this being an election year) seem to be the only important groups not interested in sports injuries as an issue. In the British Medical Journal this year (also free full text), there have been articles about the success of steroids injections in back pain, avulsion injuries of the ischial tuberosity in adolescents and human growth hormone. From the August British Journal of Sports Medicine, an article reveals how Premier League soccer teams who stretch more have fewer hamstring injuries, whilst a review of hamstring injuries suggests that underlying lumbar spine problems may be common.

http://www.injuryupdate.com.au/images/research/BJSML5nerve.pdf

Also, from this month's Sportlink, read a review of the risk factors for muscle strains.

http://www.injuryupdate.com.au/images/research/muscleriskfactors.pdf

[hhh]

regarding the stretching paper, Ian Shrier smashes it:

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.

[injuryupdate]

I also have concerns with the FA study as it is very observational, but it is a start.

I like Shrier's recent review of stretching:

Clinical Journal of Sport Medicine: Volume 14(5) September 2004 pp 267-273
Does Stretching Improve Performance?: A Systematic and Critical Review of the Literature
Shrier, Ian MD, PhD

Main Results: Of the 23 articles examining the effects of an acute bout of stretching, 22 articles suggested that there was no benefit for the outcomes isometric force, isokinetic torque, or jumping height. There was 1 article that suggested improved running economy. Of 4 articles examining running speed, 1 suggested that stretching was beneficial, 1 suggested that it was detrimental, and 2 had equivocal results. Of the 9 studies examining the effects of regular stretching, 7 suggested that it was beneficial, and the 2 showing no effect examined only the performance test of running economy. There were none that suggested that it was detrimental.

Conclusions: An acute bout of stretching does not improve force or jump height, and the results for running speed are contradictory. Regular stretching improves force, jump height, and speed, although there is no evidence that it improves running economy.

Discussion: In summary, the evidence suggests that stretching immediately prior to exercise decreases the results on performance tests that require isolated force or power. The effect on running speed remains to be determined. On the other hand, regular stretching will improve the results for all activities. This is similar to the fact that stretching immediately prior to exercise does not reduce the risk of injury, but that regular stretching may reduce the risk of injury. 6 Therefore, if one stretches, one should stretch after exercise, or at a time not related to exercise (the relative benefit of each remains unstudied at the present time). Future research should investigate the cellular and molecular mechanisms by which the effects of stretching occur, whether the added benefit of regular stretching is as effective as other types of performance-enhancement exercises being promoted (e.g., plyometrics, increased weight training), and whether the same effects are seen in the presence of injury.

Interesting conclusion that for performance (and maybe injury prevention) you should stretch, but NOT BEFORE exercise.