Injury History, Sex, and Performance on the Functional Movement Screen and Y Balance Test

Musculoskeletal injuries are an inherent risk of participation in athletes. Noncontact injuries represent approximately 20% of all injuries sustained during games and 40% of injuries sustained during practices.¹ Beck and Wildermuth² theorized that noncontact injuries occur because of a coordination failure involving a combination of high velocity and momentary loss of normal protective muscle support. Therefore, researchers^3–5 have suggested that risk factors for noncontact injuries are modifiable when identified through movement patterns, right-to-left asymmetry, or balance abnormalities. The Functional Movement Screen (FMS; Functional Movement Systems Inc, Chatham, VA) and Y Balance Test (YBT; Move2Perform, Evansville, IN) are examples of screening tools that are being used clinically to assess injury risk based on abnormal movement patterns, asymmetry, and dynamic balance.

The FMS was developed to evaluate movement performance during 7 movement patterns: deep squat, hurdle step, in-line lunge, shoulder mobility, straight-leg raise, trunk stability push-up, and rotary stability.⁶ These movement patterns are scored from 0 to 3 based on performance with or without pain or compensation, and the scores are summed for a maximal composite score (CS) of 21. This tool has been suggested to predict injury when a CS of 14 or lower is obtained in male⁷ and female⁸ athletes and male military candidates.⁹ However, the sensitivity (0.91) and specificity (0.54) of a CS of 14 to determine injury risk from the first published report⁷ has not been reproduced in the subsequent 2 studies, with one indicating a sensitivity of 0.58 and a specificity of 0.74⁸ and the other indicating that no receiver operating characteristic curve was able to maximize sensitivity and specificity.⁹ These challenges to the ability of the FMS CS to identify injury risk, coupled with well-documented sex differences^10–14 and neuromuscular changes in movement patterns after injury,^15–17 suggest that although FMS CSs may be similar between women and men or injured and uninjured individuals, these scores may be obtained with different individual movement patterns. Therefore, men and women and injured and uninjured individuals may not actually perform similarly on the FMS. To date, authors of 1 study¹⁸ have reported no sex differences in FMS performance in a young active population; however, they evaluated only the CS. Additionally, reports in the literature conflict as to the effect of previous injury on FMS performance, which may be related to methodologic differences. Schneiders et al¹⁸ found no difference in the FMS CS between recreational female and male athletes with and without injury in the previous 6 months; however, injury was not defined or identified. Peate et al¹⁹ reported that firefighters with a history of documented musculoskeletal injury were 68% more likely to have lower FMS scores than those without a history of injury.

The YBT, which is a commercially available, highly reliable tool,²⁰ was developed to standardize the modified Star Excursion Balance Test (SEBT). The SEBT was modified to improve efficiency in assessing dynamic balance and includes only 3 (anterior [ANT], posterolateral [PL], and posteromedial [PM]) of the original 8 SEBT reach directions.²¹ The YBT CS is calculated by summing the 3 reach directions and normalizing to lower extremity length, whereas asymmetry is the difference between right and left limb reach. Greater than 4 cm of ANT asymmetry during the SEBT has been suggested to predict which individuals are at risk of lower extremity injury; however, when evaluating the CS, Plisky et al²² found that only female athletes with a composite reach of less than 94% of limb length were at greater risk of injury. Recent evidence²³ has shown that sensitivity (100%) and specificity (71.1%) were maximized using 89.6% of the YBT CS to predict injury in football players; scores of less than 89.6% were associated with an injury risk that was 3.5 times greater. These results may indicate that sex differences exist in the prediction of injury risk based on dynamic balance performance as assessed by the YBT. Additionally, Steffen et al²⁴ reported that adherence to a neuromuscular-training program improved performance on the SEBT and decreased the injury risk in female youth soccer players.

Gribble and Hertel²⁵ reported differences among raw reach distances. Male participants reached farther than female participants in all 8 directions of the SEBT, but when the distances were normalized to leg length, the sex differences disappeared.²⁵ Additional data suggested that men perform better on normalized posterior reach directions, but when all 3 reach directions were averaged, no sex differences existed.²⁶ Gorman et al²⁷ showed that men performed better in normalized reach distances; however, Gribble et al²⁸ reported that women performed better in normalized reach distances. Discrepancies in the effect of sex on performance of dynamic balance may be due to small sample sizes, as the largest of the aforementioned studies included just 32 participants,²⁶ or may be due to muscle-activation differences between women and men. Whereas researchers have documented that individuals with patellofemoral pain syndrome²⁹ and chronic ankle instability^30–32 perform worse on the SEBT, additional injuries or surgeries also alter normal neuromuscular control^15–17; thus, individuals with histories of pathologic conditions that have not yet been studied may also have limitations in dynamic balance.

To date, gaps are apparent in the literature regarding the effect of injury history and sex on FMS and YBT performance in the collegiate population. Furthermore, if injury or surgery history and sex affect FMS and YBT performance in a large collegiate cohort, investigators may be able to identify an appropriate algorithm to more accurately use the outcomes of the FMS and YBT to predict injury risk in athletes. Therefore, the purpose of our study was to evaluate the effect of potential preexisting confounders of injury or surgery history and sex on performance of the FMS and the YBT in a large sample of National Collegiate Athletic Association Division I athletes. Our first hypothesis was that the sample of Division I female athletes would perform worse than the sample of Division I male athletes in FMS CS, FMS movement patterns, and YBT CS and demonstrate greater asymmetry in each of the 3 reach directions. Our second hypothesis was that the Division I participants with a history of lower extremity injury or surgery would perform worse on FMS CS and movement patterns of deep squat, hurdle step, in-line lunge, straight-leg raise, trunk stability, and rotary stability. Our third hypothesis was that the Division I participants with a history of upper extremity injury or surgery would perform worse on FMS CS and movement patterns of shoulder mobility, trunk stability, and rotary stability. Our fourth hypothesis was that the Division I participants with a history of lower extremity injury would perform worse on YBT CS and demonstrate greater asymmetry in each of the 3 reach directions.

METHODS

Health History Questionnaire

A health history questionnaire was used to assess self-reported history of injury and surgery (Figure 1). For this study, we defined injury as having experienced a previous injury and surgery as having undergone a previous surgery. Thus, for data reduction, athletes were grouped based on whether they indicated having had or not having had injuries or surgeries. For the injury and surgery history questionnaire, the participants were asked about each joint individually, except that the trunk and back were grouped together, to indicate if they had experienced injuries or surgeries. So that we could compare sexes, participants also were instructed to indicate sex.

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RESULTS

A total of 170 FMS and 190 YBT screens were completed (Table 1). The association between previous injury or surgery with FMS and YBT varied by individual joint (Table 2). Athletes with a history of hip (t₁₆₈ = −2.880, P = .005), hand (t₁₆₈ = −2.806, P = .006), or elbow (t₁₆₈ = −2.309, P = .02) injury or shoulder surgery (t_7.366 = −6.132, P < .001) performed worse on the FMS CS (Table 2). The MCID for FMS CS was 1.25. Analysis of individual FMS movement patterns revealed that participants with ankle injuries had better in-line lunge (P = .01; U = 2962; 95% CI for mean = 2.15, 2.38 [injured] versus 1.92, 2.18 [uninjured]), those with knee surgeries had worse rotary stability (P = 0.033; U = 1224; 95% CI for mean = 1.45, 2.05 [injured] versus 1.95, 2.10 [uninjured]), those with hip injuries performed worse on deep squat (P = .008; U = 899; 95% CI for mean = 0.92, 1.75 [injured] versus 1.68, 1.89 [uninjured]) and hurdle step (P = .04; U = 1117; 95% CI for mean = 1.58, 2.09 [injured] versus 1.97, 2.09 [uninjured]), those with hip surgeries had worse hurdle step (P = .002; U = 81.5; 95% CI for mean = −0.10, 2.77 [injured] versus 2.03, 2.15 [uninjured]) and in-line lunge (P = .01; U = 87.5; 95% CI for mean = −0.10, 2.77 [injured] versus 2.02, 2.19 [uninjured]), those with trunk/back injuries had better deep-squat performance (P = .02; U = 1695; 95% CI for mean = 1.74, 2.20 [injured] versus 1.56, 1.80 [uninjured]), those with shoulder injuries had worse shoulder mobility (P = .002; U = 1374.5; 95% CI for mean = 1.47, 2.25 [injured] versus 2.30, 2.57 [uninjured]), those with shoulder surgeries had worse shoulder mobility (P = .001; U = 84; 95% CI for mean = −0.24, 1.84 [injured] versus 2.26, 2.51 [uninjured]), and those with hand injuries had worse shoulder mobility (P = .02; U = 605; 95% CI for mean = 1.08, 2.42 [injured] versus 2.25, 2.51 [uninjured]) than participants without a history of injury or surgery. We found no differences in YBT CS or asymmetries when evaluating performance based on a history of lower extremity injury or surgery in individual joints (Table 2). The MCID for the YBT CS was 3.5%.

Table 1. Functional Movement Screen and Y Balance Test Composite Scores Classified by Sport and Sex

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Table 2A. Functional Movement Screen and Y Balance Test Performance Classified by Injury History

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Table 2B. Functional Movement Screen and Y Balance Test Performance Classified by Surgery History

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Table 3. Differences in Functional Movement Screen and Y Balance Test Performance Classified by Sex

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When individual joint injuries or surgeries were grouped as lower extremity, trunk/back, and upper extremity, we found no differences in FMS CS; YBT CS; or YBT ANT, PM, or PL asymmetry among participants with a history of lower extremity injury or surgery; however, a history of trunk/back injury contributed to larger asymmetry ranges in both the ANT and PM reaches (Figure 2). Participants with a history of upper extremity injury or surgery performed worse on the FMS CS (Figure 2).

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We found no differences between female and male athletes in FMS CS (t₁₆₈ = 0.907, P = .37; Table 3). Female athletes performed worse than male athletes in trunk stability (P < .001; U = 2438; 95% CI for mean = 1.54, 1.99 [women] versus 2.18, 2.54 [men]) and rotary stability (P = .01; U = 3055.5; 95% CI for mean = 1.71, 1.92 [women] versus 1.87, 2.11 [men]); however, female athletes performed better than male athletes on in-line lunge (P = .008; U = 2928.5; 95% CI for mean = 2.03, 2.27 [women] versus 1.75, 2.03 [men]), shoulder mobility (P < .001; U = 2429.5; 95% CI for mean = 2.30, 2.67 [women] versus 1.81, 2.19 [men]), and straight-leg raise (P < .001; U = 2059; 95% CI for mean = 2.33, 2.68 [women] versus 1.87, 2.13 [men]). We found no differences in performance on the deep squat (P = .10; U = 3130; 95% CI for mean = 1.51, 1.80 [women] versus 1.66, 1.96 [men]) or hurdle step (P = .87; U = 3571; 95% CI for mean = 1.89, 2.06 [women] versus 1.87, 2.04 [men]) between female and male athletes. Their YBT CSs were similar (t₁₈₈ = −1.920, P = .052; Table 3). However, female athletes demonstrated less asymmetry than male athletes in YBT ANT (t₁₈₈ = −1.920, P = .02), whereas asymmetry was similar in YBT PM (t₁₈₈ = −1.529, P = .13) and YBT PL (t₁₈₈ = 0.322, P = .75; Figure 3).

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DISCUSSION

The FMS and the YBT are being used clinically to identify athletes at risk of injury^{7–9,19,22,23} and subsequently to administer programs to decrease injury risk³⁷; however, differences exist in movement patterns and balance between athletes who have and have not been injured and between female and male athletes.^{10–17,21,26–30,38–41} Therefore, the purpose of our study was to evaluate the effect of potential preexisting confounders of sex and injury or surgery history on performance of the FMS and the YBT in a large sample of Division I athletes.

We found no difference between female and male athletes in FMS CS; however, female and male athletes performed differently in all movement patterns of the FMS except for the deep squat and hurdle step. Researchers⁶ have suggested that the deep squat is a movement needed in most sports. If true, this may be why female and male Division I athletes appear to perform this task with similar scores. Division I female and male athletes also perform similarly in the hurdle step, which researchers have suggested requires coordination and stability between the hips and torso along with dynamic balance,⁶ and the YBT, which requires dynamic stability during contralateral limb reaching. These findings indicate that the female and male athletes in our study had similar dynamic balance. Researchers^25,26 have demonstrated no difference between sexes in performance on the YBT with small sample sizes. Our study is the largest reported to date with adequate power (1.0), minimizing the risk of type II error. Our findings, coupled with those reported in smaller previous studies, show that sex differences likely do not exist in performance of the YBT when evaluating the CS.

Whereas we hypothesized that Division I female athletes would perform worse than Division I male athletes in the FMS CS and movement patterns, we found that they performed worse on tasks that may involve greater core coordination with an appropriate transfer of energy through the trunk (ie, trunk stability and rotary stability) but better on tasks that involve greater flexibility and joint mobility (ie, in-line lunge, shoulder mobility, and straight-leg raise). These findings may indicate that Division I female athletes have an increased risk of injury, as decreased core stability has been hypothesized to increase injury risk.⁴² Our results suggest that, although female and male Division I athletes performed similarly on the overall FMS score, FMS CS was not achieved in the same manner; this is similar to findings reported in recreational athletes.¹⁸ Therefore, future researchers should evaluate if sex biases the association between FMS CS and injury. They also need to observe differences in individual movement-pattern performance to truly determine individualized injury risk, as Kazman et al⁴³ recently proposed that the FMS CS lacks internal consistency and validity. Additionally, assessing differences between women and men and specific FMS movement patterns may aid in structuring any subsequent training on an individualized, sex-specific basis.

Evaluation of sex as a confounder also may be necessary when assessing performance on the YBT, as Division I male athletes had greater ANT asymmetry than Division I female athletes (Figure 3). This finding directly contradicted our hypothesis that female athletes would demonstrate greater reach asymmetry than male athletes. Based on previous research,²² this may suggest that the Division I male athletes in our study could be at risk of lower extremity injury, as they had more than 4 cm of ANT asymmetry. However, the study design did not enable us to determine why men in our study had greater ANT asymmetry. Investigators⁴⁴ have indicated that collegiate athletes participating in soccer, which requires reaching outside the base of support during functional activities, performed better in dynamic balance than athletes involved in basketball, which primarily stresses the sensorimotor system within the base of support. Perhaps participation in sport modulated symmetric performance in the ANT task in our study, as most of the male athletes whom we sampled were football players. In addition, the YBT possibly challenged the sensorimotor system more in the football players in our study and, thus, was associated with greater ANT asymmetry in male than female athletes. This may suggest that, when football players are in positions that are outside their base of support, they may have altered neuromuscular responses and, therefore, a greater risk for injury. Sport-related neuromuscular factors may influence performance on the SEBT; collegiate female soccer players reached farther than female nonsoccer recreational athletes in the ANT and posterior reach directions.⁴⁵

In previous studies,^7–9 the FMS has been used to predict injury. However, injury history, which has been suggested as the best predictor of injury risk,^46,47 was not assessed in these studies. As such, poor performance on the FMS may actually reflect injury history rather than predict future injury risk. To date, athletes who score less than 14 on the FMS have experienced a higher proportion of injuries.^7–9 Our results demonstrated that Division I athletes with a history of hip, elbow, or hand injury or shoulder surgery performed worse (FMS CS = 12.7, 12.1, 12.3, and 12.0, respectively) than athletes without a history of injury or surgery (FMS CS = 14.4, 14.3, 14.3, and 14.3, respectively; Table 2). If we did not account for injury or surgery history in these athletes, their FMS CSs would suggest, based on the literature,^7–9 that they were at risk of future injury. However, they quite possibly are at risk for future injury based on their history, or the FMS CS may actually be detecting previous injury rather than predicting future injury risk. Therefore, clinicians need to look not only at scores on screening tools, such as the FMS and YBT, when evaluating injury risk but also need to assess previous history. Previous history may provide a more accurate predictor of performance on these screens and subsequent injury risk than assuming that, because an athlete performs poorly on these screens, he or she is at greater risk for injury.

Our results are similar to those of Peate et al,¹⁹ who reported that firefighters with previous injury were more likely to perform worse on the FMS, but contradicts the findings of Schneiders et al,¹⁸ who did not observe a difference in FMS performance by those who had sustained an injury in the 6 months before the study. Perhaps evaluating overall injury history rather than only injuries that have occurred recently is important. Discerning whether the risk of future injury is identifiable based on FMS performance or injury history is impossible if researchers have not assessed and accounted for injury history.

In addition, participants with a self-reported history of lower extremity injury or surgery performed worse on deep squat, hurdle step, in-line lunge, and rotary stability depending on the body part that was injured, whereas participants with a self-reported history of upper extremity injury or surgery performed worse on shoulder mobility. Interestingly, participants who self-reported a trunk/back injury performed better on the deep squat, and participants who self-reported an ankle injury performed better on the in-line lunge. Although we could not determine why participants with trunk/back and ankle injuries performed better on the deep squat and in-line lunge, respectively, this finding may reflect improved neuromuscular control or improved range of motion gained through effective postinjury rehabilitation. Inani and Selkar⁴⁸ reported that patients with nonspecific low back pain had improved functional status after 3 months of core-stabilization exercises; thus, our participants may have had improved core stability, which was reflected in improved performance in the deep squat. Gutierrez et al¹⁵ found that individuals with chronic ankle instability demonstrated increased preparatory and reactive activation of the peroneal muscles in response to a supination event, suggesting an enhanced response to promote dynamic restraint. Macklin et al⁴⁹ demonstrated that runners with ankle-joint equinus had improved ankle-joint dorsiflexion after a triceps surae stretching program. Perhaps our participants had enhanced dynamic restraint or ankle range of motion and, therefore, were able to perform better in the in-line lunge. Specific joint injuries or surgeries resulted in increased or decreased performance on select FMS movement patterns, again suggesting that performance on the FMS may actually reflect injury history rather than predict future injury risk.

Although we did not find that injury or surgery history influenced performance on the YBT, these results are consistent with a recent report that injury history did not influence YBT performance in collegiate football players.²³ Whereas injury or surgery history did not affect performance on the YBT or contribute to reach asymmetries, the 95% CIs indicate that participants with trunk/back injuries had greater variability in YBT reach asymmetry than participants without trunk/back injuries (Figure 2). The combination of reported altered neuromuscular control of the trunk as a predictor of knee-injury risk⁵⁰ and our findings of greater variability in YBT performance may suggest that athletes with a history of trunk/back injury are at greater risk for lower extremity injury. Furthermore, the large deviations seen in YBT performance and reach asymmetry in participants with a history of trunk/back injury demonstrate that, when individuals are grouped, potentially meaningful asymmetric movement patterns may be lost. Therefore, individual injury histories should be examined before assuming that injury risk is similar based solely on scores obtained from the FMS and YBT.

We are the first to assess injury history and sex differences in the FMS CS and individual movement-pattern scores and YBT CS and reach asymmetries in a large sample of Division I collegiate athletes. Whereas our sample represented the percentage of athletes who participate in each sport relative to the total number of athletes in a Division I institution, most of our male participants were football players; this may have limited our findings, as the neuromuscular system is developed through previous experiences. Injury history was self-reported; we possibly did not have a complete picture of each athlete's previous injuries. However, self-report is the most common method of injury reporting used during collegiate preparticipation examinations. Additionally, although we asked about injury to each joint, we did not assess concussion history and did not ask about the types or numbers of previous injuries. We aimed to assess if participants had previous injuries or surgery; we did not classify injury or surgery based on type of injury or surgery type or time since injury or surgery had occurred. Injury severity, time since previous injury or surgery, or rehabilitation after injury or surgery may have affected findings. Future researchers should consider these factors.

CONCLUSIONS

Whereas Division I female and male athletes may perform similarly in FMS and YBT CS, differences appear in some FMS movement patterns and YBT ANT asymmetry. Female athletes performed better on FMS movement patterns involving flexibility and balance but worse on movement patterns associated with core strength. Investigators should consider assessing sex as a confounder in future research. Injury or surgery history did not affect overall YBT performance. It indicated differences in some FMS and YBT movement patterns but not necessarily the overall score. Therefore, evaluating FMS or YBT movement patterns rather than just overall scores in athletes with previous injury or surgery may be appropriate.