Ehrmann, FE, Duncan, CS, Sindhusake, D, Franzsen, WN, and Greene, DA. GPS and Injury Prevention in Professional Soccer. J Strength Cond Res 30(2): 360–367, 2016.

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To the Editor:
I read with interest the article by Ehrmann et al. (3). This article investigated the relationships among global positioning system (GPS) variables measured and injury occurrences in professional soccer. Two issues attracted my interest: the small sample reported and the identification of 2 GPS variables as noncontact soft-tissue injury predictors. The study used a sample of 19 elite soccer players competing in the Australian Hyundai A-League. I believe that this sample size is too low to answer questions about injury prevention. As reported, 16 injuries occurred in 11 players. Therefore, this study offers a limited number of cases throughout the season, in contrary to previous studies that used larger samples (1,6). Moreover, injuries are generally associated to several factors, such as age, previous injuries, etc. (2,4,5). In this study, these factors were not taken in account, which may have affected the results. One of the questions could be: were there reinjuries? Limited information on this issue was reported in the study. My second concern is in relation to the “identification” of 2 GPS variables as noncontact soft-tissue injury predictors. This study reported (Table 3) that averages for meters per minute during the 1- (89.00 m·min−1) and 4-week blocks (88.28 m·min−1) preceding the injuries were greater than the season average meters per minute for the 1- (80.99 m·min−1) and 4-week blocks (82.12 m·min−1), respectively. The authors stated that average meters per minute was the only variable that demonstrated a real measure of session intensity with respect to duration. It seems that there was too much speculation in the discussion of this parameter; therefore, it would be necessary to consider other parameters recorded during this research. Total distance was greater during the season average than the 1-week blocks (7103.74 and 6511.52 m, respectively) and the season average compared with the 4-week blocks (7137.87 and 6847.97 m, respectively). This statistical trend was also found for average new body load such that the 1- (133.07 Arbitrary Units [AU]) and 4-week blocks (142.93 AU) were less than the season averages (158.82 and 158.51 AU, respectively). Greater season averages for new body load were in agreement with greater season averages for total distance covered, but in contrast to lower season averages for meters per minute compared with the preceding injury blocks. In the study, there are discrepancies among the variables identified; thus, the study does not offer clear conclusions. Contrary to what it is shown, other literature shows that injury risk is associated with total distance (1). In conclusion, the sample size considered in this study is small, and the discrepancies among the total distance and new body load versus meters per minute do not adequately support the conclusions.
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