DISCUSSION
This systematic review and meta-analysis assessed the literature to determine whether there is an association between an FMS score of less than 14 out of 21 points and subsequent injuries and whether it could serve as a useful tool. The results suggest the association is not clear. It has been observed that the results do not offer strong arguments in favour of the 14/21 cut-off, which is widely used in the literature since the results reported by Kiesel et al.9 Only half of the studies to date have shown the discriminating use of the FMS. The focus on using a score of 14/21 to avoid the variability in other cut-offs reported by other systematic reviews23–26 did not support the association between the FMS and subsequent injuries. However, an analysis of previously published systematic reviews showed that the cut-off was initially set at 14/21, but actually studies with a score of 14 (±3)/21 were analysed. This should suggest the possibility of proposing, instead of a specific cut-off point, a range of scores that allow the screening from a qualitative rather than a quantitative point of view. In this way, functional capacities at different levels could be stratified and the association according to the category analysed.
Association between FMS score and injuries
Five out of 12 studies, in addition to the female sample from the study of Knapik et al,31 demonstrated that FMS score was associated with subsequent injuries. This systematic review did not confirm that the 14/21 cut-off was associated with subsequent injuries. According to another systematic review, 6 of 15 results on the association between FMS score and injury risk (OR or risk ratio) showed a significant effect.23 Perhaps performing a stratification by levels (integrating different cut-off points) of functional capabilities of the subject could be a qualitative screening method that facilitates the functional analysis (and association with injuries) of the FMS.
One of the possible reasons for these differences may be the definition of the injury in each article. The different criteria used by the different studies make it very difficult to compare across them and helps to understand the poor evidence that was represented in the systematic reviews. For example, we could divide the definitions according to medical criteria31 32 35 38 40 or according to the time since the last sports activity.9 33 34 36 39 41 42 These criteria are very difficult to compare; in addition, the time since last sports activity ranges from 1 day to 4 weeks according to each article. Also, the fact that they do not take into account previous injuries cannot be ignored. A review in 2014 regarding injury risk and runners concluded that the main indicator of risk was being injured in the previous 12 months.43 A previous injury could influence the FMS score because it is possible that subjects will score worse. To improve the comparison, the definition of injury must follow the same standards according to a reference test.
The different samples and follow-up used in each study did not influence the results. If we divide studies into short-term follow-up (0–4 months)31 34 35 38 40 and long-term follow-up (4 months–1 season),9 32 33 35 37 39 41 42 the results that are in favour of the FMS having an association with the likelihood of injury were distributed in both groups, so it was impossible to define the tendency of a relationship with injuries according to follow-up. The risk of bias in the short-term follow-up studies was low,23 and only one study did not obtain results in favour of the FMS. Despite the advantage of short-term follow-up, other methodological factors have been more decisive. With respect to the sample size, there are inconclusive relationships as with the follow-up. The follow-up and the sample size are important factors to take into account in subsequent studies.
Gender differences and the risk of injury have been studied in the literature.44 45 According to the results by gender, the FMS score was a significant risk factor in women (OR=2.41, 95% CI 1.38 to 4.22) who participated in the study of Knapik et al.31 However, for men who participated in the sample of the same study, the FMS score was not a risk factor (OR=1.18, 95% CI 0.82 to 1.69). If these results are compared with Chorba et al
32 and Kodesh et al,38 FMS score was not a significant risk factor for women in both studies (OR=4.58, 95% CI 0.99 to 21.13 and OR=1.29, 95% CI 0.67 to 2.51). A notable difference between the two samples was that the study sample of Knapik et al
31 was bigger (n=275) than that of Chorba et al
32 (n=38) and Kodesh et al.38 In short, methodological biases would have to be minimised to better interpret the results46 because the comparison between men and women is important to confirm that injury prevention strategies should be specific to each gender.47
Finally, the variability in the sensitivity (0.26–0.83) and specificity (0.46–0.91) is huge, and previous studies have rendered the 14/21 score doubtful. Most of the selected studies decided to find a better cut-off, and a sensitivity and specificity analysis of other cut-offs was carried out. Within the studies selected in this systematic review, Mokha et al
41 obtained a better sensitivity (0.83) and specificity (0.88) with 16 as the cut-off, and Knapik et al
31 with a cut-off score of 12 in the male sample obtained a sensitivity of 0.22 and specificity of 0.87. There are other examples in the literature with other cut-offs with better sensitivity and specificity, such as Letafatkar et al
48 which used a cut-off of 17 with good sensitivity (0.64) and specificity (0.78). On the contrary, there are no firm results that establish an acceptable cut-off point with excellent results49 in sensitivity and specificity except for the study of Mokha et al.41 Therefore, a sensitivity and specificity analysis in each study is a good option to find the best cut-off due to the variability in design, as has been shown before.
Homogeneity of the meta-analysis
The meta-analysis from the systematic review confirmed that there was some heterogeneity in the selected results. The selected studies reflected substantial heterogeneity (I2=70%) according to Higgins and Green,30 as the value was between 50% and 90%. The differences discussed above could create great variability which could be caused by the level of heterogeneity, so the overall OR (2.03, 95% CI 1.23 to 3.35) is not a valid value due to the poor homogeneity of the selected studies.
If other systematic reviews on the FMS and subsequent injuries are compared with the current study, both come to an agreement that the precision of the FMS for prediction of the risk of injury is low and that its effectiveness could not be verified. Dorrel et al
26 performed the first systematic review on the FMS, and a conclusion was obtained after a meta-analysis of the diagnostic reliability, which showed that the FMS had low sensitivity (0.24) and good specificity (85.7). The authors proposed that each study should look for its cut-off according to its sample and definition of the lesion since, as it has been confirmed in this review, using the same cut-off score does not achieve better solid results.26 When compared with the results of Moran et al,23 the current review obtained better results in the meta-analysis (OR=1.47, 95% CI 1.22 to 1.77, I2=57%), but they used three studies and a military male sample. Having similar samples and the definition of the lesion very close, by medical decision, confirmed the importance of having minimum heterogeneity in the studies, emphasising that there was no uniformity in the selected articles in the three reviews. The meta-analysis outcomes presented in this review of 12 studies, with a larger number of different samples and with both genders included, increased the heterogeneity. To conclude, there are no findings that support a relationship between FMS score and injury risk.
The lack of consensus is common in this kind of tools because there are other tests that need to be further investigated.50 51 Lisman et al
52 and O’Connor et al
35 used Physical Fitness Tests (PFTs) along with FMS. A PFT score of less than 280 was a risk factor (OR=2.1, 95% CI 1.5 to 2.9) with a male sample. Lisman et al
52 specified that a PFT that could significantly predict a risk factor was the 3-mile run in more than 20.5 min (OR=1.72, 95% CI 1.29 to 2.31). In contrast, the PFT had limited and conflicting evidence regarding reliability and validity in common usage.53 Future studies should better define the sample, the definition of the injury and the methodology because the FMS is far from being a good tool to identify a high risk of injury to the individual.54
Methodological quality
We noted a wide range in the methodological quality of the studies that comprised our systematic review. There was too much difference between the scores used as a reference in the different studies. Theoretically, the cut-off should be 14, but they actually ranged from 11 to 18. Importantly the five studies that had the poorest method scores were those studies that confirmed the relationship between a low FMS score and injury.9 31 34 37 42 According to Bahr,55 the majority of studies on injury prediction were inappropriately designed because they did not explain the causative factor with sufficient accuracy. Therefore, the lack of good methodology could influence the information, and the limited methodology could detriment the results of the systematic review and the heterogeneity of the meta-analysis.
Clinical importance
Although many sports teams use the FMS at the beginning of the season, there is no evidence to confirm its association with injuries. Sport has been the starting point to identify the importance of having good tools to predict injuries; however, other types of assessments must deal with physically demanding tasks.56 Most of the selected studies included samples related to sports or workers that required good physical condition. A good initial assessment could help reduce the time lost in a competition or work, and reduce the costs associated with injuries.57
Due to its ability to evaluate stability and strength, and because it is easy to administer and perform and is very adaptable to the clinical environment,13 14 the FMS could be a good tool for clinicians and physiotherapists. Despite the advantages that the FMS may have in clinical practice, according to the selected studies the association between FMS score and injuries is limited, and due to the heterogeneity of the data there can be no consensus on what should be the reference score to use for the FMS as a predictive tool for injuries. Therefore, it is necessary to focus on the nature of the patient in daily practice and individualise the clinical information collected.
Limitations
The study has some limitations. The number of studies included in the review was small. The meta-analysis showed that the OR of the selected studies had a heterogeneous distribution. The definition of injury was not very similar in the studies and could be a reason for this heterogeneity. From a methodological point of view, we used the most well-known appraisal tool for observational studies—STROBE. Other tools more focused on diagnosis could be more adjusted to the topic, but since the FMS is not a conventional diagnostic tool we could clearly and concisely score and classify the quality of the articles included using STROBE.
The samples used in the studies were quite similar because subjects were young and were in sports or had a very good physical condition. It would be interesting to see how it affects other people, because the risk of injury increases with age,58 and using participants who are not involved in sports in prospective studies.