Movement screens: Are we measuring movement dysfunction or movement skill?

Introduction

Movement screens are commonly used tools for assessing athletic readiness. These screens typically consist of multiple movement assessments requiring athletes to coordinate both unilateral and bilateral movements over large ranges of motion and through fundamental movement patterns such as squatting or lunging.^1–3 By visually observing an athlete’s movement patterns, coaches or clinicians are able to identify deficits in the athletes’ mobility or strength and can then take appropriate corrective measures. Poor performance on movement screens is suggested to be a risk factor for noncontact injuries.^4–6 Therefore, corrective measures often involve the prescription of strength programs or therapeutic interventions designed to improve mobility or strength, and theoretically reducing injury risk, the programming of which is directly based on observed movement deficits.

A fundamental assumption underlying the hypothesis that corrective programming can reduce injury risk is that the faulty movement patterns observed truly reflect movement dysfunction and are not simply due to a lack of movement skill. In other words, the coach must be able to tease out whether the athlete simply does not know how to perform the requested movement or whether they are not physically capable of performing the movement. Central to the ability to separate the two are the instructions, demonstrations, and practice opportunities provided to the athlete prior to performing the movement screen. Numerous studies have shown that providing a visual model of the desired movement enhances both coordination and rate of learning during subsequent performances of the same movement, with the effects being especially pronounced with novel movements.^7–10 Other authors have documented that providing verbal cues and corrective feedback facilitates rapid improvement in subsequent movement trials.^11–13 Finally, a large body of literature documents how using verbal instructions designed to manipulate an athletes’ focus of attention, and specifically using an external focus of attention, improves movement performance.^14–17

Given the importance of using demonstration, allowing practice with feedback, it is problematic that many movement screens recommend on athlete perform the screens without having observed the movement, warmed up, performed any practice trials or received any feedback, and that they are given limited instructions. To date, how these various factors influence movement screen performance has seen minimal investigation. A recent study by Frost et al. ¹⁸ found that movement screen scores improved when participants were provided knowledge of the grading criteria. As a result the authors suggested that movement screens may not be capturing movement “dysfunction.” ¹⁸ However, how other factors such as using demonstrations or allowing practice influence movement screen performance, and the subsequent conclusions one might draw regarding movement “dysfunction” verse movement skill, has yet not been investigated.

Therefore, the purpose of this study was to compare performance on the overhead squat (OHS) when participants performed the movement with no instruction (BASE condition), instructions used with a popular commercial movement screen (CMS condition), and instructions which were developed based on principles of motor control and learning which included verbal instruction and cues, demonstration of the desired movement, and practice trials with feedback prior to evaluation (IDP condition). The OHS was specifically chosen as it is incorporated into numerous commonly used CMSs.^2,3,19,20 We hypothesized that performance on the OHS would be better in the IDP condition than in either the BASE or CMS conditions, as marked by a lower squat, greater range of motion at the hip, knee, and ankle, a more upright torso, and parallel alignment of the torso and shank throughout the squat.

Methods

Results

Symmetry of weight distribution was not different between instructional conditions (F_2,26 = 2.53, p = .095; Figure 2(a)). COM displacement was significantly different between conditions (F_2,26 = 8.32, p = .001; Figure 2(b)). Post hoc comparisons using least significant differences revealed participants lowered their COM significantly more in the IDP condition (0.47 ± 0.67 m) than in either the Baseline (0.41 ± 0.08, p = .003, ES = 0.872) or the CMS conditions (0.43 ± 0.07, p = .022, ES = 0.475). Baseline and CMS conditions were not statistically different, but demonstrated a moderate effect size (p = .07, ES = 0.426). OPEN IN VIEWER

Peak forward lean of the torso was not significantly different between instructional condition (F_2,26 = 1.103, p = .347; Figure 3(a)). For all three instructional conditions paired t-tests revealed there were no differences in torso and shank orientation at the deepest point of the squat between left and right sides (baseline p = .312, CMS p = .417, and IDP p = .535). Therefore, the average of the left and right sides was used in the ANOVA, which showed that the difference in orientation between the torso and shank differed between instructional conditions (F_2,26 = 5.605, p = .009; Figure 3(b)). Multiple comparisons using least significant difference revealed the difference in orientation between the torso and shank was smaller in the IDP condition (9.52 ± 5.14°) than in either the baseline (15.79 ± 10.78°, p = .015, ES = 0.742) or the CMS (13.72 ± 10.16°, p = .039, ES = 0.522) conditions. The Baseline and CMS conditions were not different (p = .216, ES = 0.198). Horizontal distance between the bar COM and whole body COM at the deepest point in the squat was not different between instructional conditions (F_2,26 = 1.122, p = .341; Figure 3(c)). OPEN IN VIEWER

For all three instructional conditions paired t-tests revealed no statistically significant differences between left and right sides for peak hip flexion (baseline p = .571, CMS p = .361, and IDP p = .827), peak knee flexion (baseline p = .662, CMS p = .861, and IDP p = .480), or peak ankle dorsiflexion (baseline p = .807, CMS p = .826, and IDP p = .722). Therefore, the average from left and right sides was used in the ANOVA. Average peak hip flexion was significantly different between instructional conditions (F_2,26 = 7.852, p = .002). Multiple comparisons using least significant differences showed participants had greater peak hip flexion in the IDP condition than in the Baseline (p = .002, ES = 0.399) or CMS conditions (p < .001, ES = 0.231; Table 1). The Baseline and CMS conditions were not different (p = .205, ES = 0.175). Average peak knee flexion was also significantly different between instructional conditions (F_2,26 = 5.142, p = .013). Similar to peak hip flexion, participants demonstrated greater peak knee flexion in the IDP condition than in the Baseline (p = .012, ES = .546) or the CMS conditions (p = .007, ES = 0.308; Table 1). Again, Baseline and CMS conditions were not different (p = .306, ES = 0.212). Average peak ankle dorsiflexion was not different between instructional conditions (F_2,26 = 2.593, p = .093; Table 1).

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Table 1.

Peak hip, knee, and ankle flexion during the overhead squat.

	Baseline	CMS	IDP
Peak hip flexion (°)	95.58 ± 10.91	97.53 ± 10.99	100.16 ± 11.98 a
Peak knee flexion (°)	104.43 ± 16.50	108.23 ± 19.07	114.03 ± 18.59 a
Peak ankle dorsiflexion (°)	29.06 ± 6.51	29.99 ± 6.56	30.73 ± 7.23

Discussion

Movement screens are rapidly increasing in popularity as tools for assessing an athlete’s athletic readiness or potential injury risk. However, in many cases a distinction between movement dysfunction and movement skill are not clearly being delineated. The motor control and learning literature clearly demonstrates the performance benefits when participants are provided instructions, verbal cues, demonstration, and practice. In light of this, the purpose of this study was to examine the effects of instruction, demonstration, and practice on performance of the OHS, an exercise incorporated into many commonly used movement screens. We hypothesized that performance on the OHS would improve under the IDP condition compared to BASE and CMS conditions. The results support our hypothesis. Participants demonstrated greater vertical displacement of the COM, and greater peak hip and knee flexion angles under the IDP condition than either the BASE or CMS conditions, meaning participants squatted deeper during the IDP condition. The large effect sizes for COM displacement, and moderate effect sizes for peak hip and knee flexion suggest that both the hip and knee contributed equally to the increased depth of the squat. Additionally, the differences in the orientation of the torso and shank were smaller in the IDP condition than the BASE or CMS conditions. One of the key evaluation criteria for the OHS is whether there is a parallel alignment between the torso and shank at the bottom of the squat.^2,5 The smaller difference in the orientation of the torso and shank suggest not only did participants squat deeper in the IDP condition but did so with better posture and alignment.

While the results of this study may be considered axiomatic given the large volume of motor learning literature emphasizing the importance instruction, demonstration, and practice, they still have important implications for how coaches or clinicians incorporate movement screening into their daily practice. The purpose of movement screening is to identify dysfunctional movement patterns in order to decrease risk of injury and enhance performance, ² and not to assess deficient movement skill. As such, it is critical that athletes know how to perform a movement correctly before being assessed in the screen otherwise one cannot separate true movement dysfunction from a lack of movement skill. In other words, the athlete may be physically capable of performing the movement, they just do not know how to perform it correctly. For example, the movement screen in the current study, the OHS, is commonly used to assess bilateral mobility of the hips, knees, and ankles, with failure to squat deep enough or heels rising off the ground being indicative of limited mobility in these joints. ² However, when an athlete is properly instructed in how to perform the OHS, allowed to practice, and receives corrective feedback during that practice, then they are immediately able to squat deeper, with increased hip and knee flexion. As a result, the conclusion of limited mobility in the hips and knees would no longer be valid.

In addition to identifying initial dysfunctional movement patterns, our results also call into question the practice of re-administering a movement screen in order to assess improvements in the original dysfunction. Often movement screens are administered at the start of a season and again after some type of corrective exercise program has been performed, with improvements in scores being interpreted as a reduction in “dysfunction.” It is possible the improvement in scores may have nothing to do with improvements in dysfunction. For example, Frost et al. ¹⁸ showed that performance on a commercially available movement screen improved simply by instructing individuals on the goals of each test. As a result they questioned whether movement screens are capable of quantifying improvements in “dysfunction.” Our results support this assertion, with the caveat that perhaps it is not knowledge of the goals, but the individual having a better motor representation (skill) of the desired movement which resulted in the increased performance. However, we did not explicitly test this and further research is required to understand the various mechanisms responsible for improving movement screen performance.

Our results also suggest that the reliability of the OHS itself may be a concern and requires further investigation. Several studies have evaluated the inter-rater, intrarater, and test–retest reliability of movement screens which incorporate the OHS as one component.^27–30 However, these studies only analyzed the reliability of individual components or the composite movement screen score. They did not examine how modifying the instructions influences the reliability of the movement. The fact that we observed significant changes in movement performance with only a few minutes of instruction suggests the OHS may not be as reliable as thought when performed without proper instructions. While further research is required to confirm this, based on our results we recommend coaches and clinicians critically evaluate how they use the OHS and any information it yields as part of their regular athlete screening protocols.

If coaches or clinicians desire to continue incorporating movement screening into their regular practice then we suggest they do so with consideration of the motor learning principles underlying this study. Improved motor performance after observing a demonstration has been previously documented for numerous complex motor activities including throwing, ⁷ volleyball sets and serves, ⁹ figure skating jumps, ¹⁰ and dart throwing. ³¹ The exact mechanisms by which this happens are not clear, but several hypothesis have been proposed. Custers et al. ³² suggested that in the course of observing a model of the desired movement learners acquire a symbolic representation of the activity which serves as a guide for subsequent performance changes toward the desired model. Similarly, Horn et al. ⁷ suggested that demonstration may serve as a rate enhancer which provides learners with a rapid solution for figuring out how to do novel movements. In addition to the beneficial effects of demonstration, previous work by Schmidt ³³ suggests that practice is essential for optimal motor performance, especially during early skill acquisition as it allows performers to construct a better motor representation of the skill. Finally, Horn and Williams ³⁴ showed that movement can be further improved by providing feedback during practice, and that the efficacy of feedback is enhanced with prior demonstration. In other words, the prior demonstration may put learners in a position where they are better suited to receive verbal coaching or instructions regarding a specific movement task.

Applied to the movement screening, these motor learning principles all help explain why performance on the OHS improved in the IDP condition. Often the movements required on a movement screen are a novel task, especially if the individual has never performed a movement screen previously. Thus, the demonstration both provides individuals with a model for how to perform the movement correctly and enhances the rate at which they adopted this model. Additionally, already having the model improves their ability to incorporate the subsequent corrective feedback and cues they receive during their practice trials. Overall, this leads to a better performance on the movement screen.

There are several limitations to the current study which must be considered in interpretation of the results. First, all participants had no previous experience performing movement screens or the OHS movement. Despite this, they were able to rapidly improve their performance when provided verbal cues, demonstration, corrective feedback, and practice. Whether these same improvements would have been observed with individuals who have performed movement screens before or are experienced with the OHS is not clear. Secondly, our IDP condition included demonstration, practice, and verbal instructions. Overall, these combined conditions improved performance on the OHS, but we cannot separate out whether one factor had more impact than the others. It may be that simply observing a demonstration of the movement prior to performing the test would improve performance. Or it may be that specific phrases within our instructions such as ‘while squatting think about staying tall with a big butt and chest’ were enough to change the participant’s movement. Separating out the relative contributions from each factor requires further research. Finally, we only analyzed on activity, the OHS. While this activity is commonly incorporated into many movement screens, these screens also include other movements as well. Whether the differences observed on the OHS transfer to other activities, and as a result, improve overall movement screen scores, requires further study.

In summary, the results of the current study suggest performance on the OHS, one exercise typically incorporated into movement screens, can be quickly and easily improved by considering the influence of demonstration, instructions, and practice on subsequent movement performance. Since movement screens are designed to assess athletic readiness or injury potential it is important to provide an optimal motor learning environment for the athlete, one which allows them to complete the movement to the best of their ability. Failure to do so may result in incorrectly interpreting the athletes’ lack of movement skill for movement dysfunction and lead to unnecessary training prescriptions for that athlete. Coaches and therapists can easily adopt methods similar to those used in this study when using movement screens to assess their athletes. Specifically, coaches should consider incorporating simple modifications to their verbal instructions, add demonstration when describing the task, and allow participants to practice before being evaluated. These steps will improve the overall accuracy of movement evaluations by separating out movement skill from potential dysfunction or asymmetries in movement. The results of our study also suggest that performing movement screens without allowing the athlete to warm up or to practice the movements may not accurately depict their true movement capability. Often this approach is used as some practitioners want to “evaluate an athletes’ natural movement.” However, this claim does not allow for a distinction between an athletes’ movement skill and their physical ability to perform a certain movement. Separating these two is critical for properly programming interventions resulting from movement screen performance.