Abstract
Single leg movement screens provide valuable information to practitioners when evaluating unilateral weightbearing control. The ability to maintain proper alignment of the trunk, pelvis, and lower extremity are often assessed during single leg movement screens such as the single leg squat (SLS), forward step down (FSD), and lateral step down (LSD). Each of these tasks examine an individual’s ability to lower and raise their center of mass while maintaining balance and proper mechanics (i.e., upright trunk position, neutral pelvis). Movement patterns identified by these tasks such as ipsilateral trunk lean, pelvic drop, and knee valgus that are known to place excessive forces on lower extremity joints and considered to be a sign of inadequate motor control. The ability of these tasks to identify the abovementioned factors provides utility for practitioners when screening movement and tracking the rehabilitation process. Additionally, the unilateral nature of the SLS, FSD, and LSD allow for the analysis of bilateral differences that may be associated with increased injury risk. Current research supports the idea that healthy individuals have symmetrical lower extremity movement during single leg weightbearing movements. Thus, rehabilitation protocols often assume symmetry prior to the injury and subsequently will utilize the unaffected leg as a benchmark for treatment goals. However, conventional research has focused on group analyses that have been found to obfuscate asymmetrical movement patterns that are occurring at the individual level. The masking of asymmetrical movement patterns at the group level is due to the dichotomization of legs by the dominant (i.e., the leg used to kick a ball) and non-dominant leg. Historically leg dominance, or preference, were arbitrarily selected as the dynamic leg used to kick a ball. However, this series of studies illustrates the importance of identifying a task specific method of identifying limb preference when performing clinical assessments from a group analysis perspective.
The overall purpose of this dissertation was to examine 1) potential differences in the movement patterns of three single leg weightbearing tasks (e.g., SLS, FSD, LSD), 2) whether performing these tasks resulted in asymmetrical mechanics, and 3) whether asymmetrical movement patterns could be corrected with an intervention. To address this purpose, two separate data collections were collected using convenience samples. The results of the first study provided the foundation for the clinical task used for the intervention of the culminating study.
The purpose of the first manuscript was to assess potential differences in the movement patterns of healthy individuals during the SLS, FSD, and LSD. To identify differences between tasks, kinematic waveforms in the fontal and sagittal plane of the trunk, pelvis, hip, and knee were analyzed. Primary findings indicated that the FSD provoked greater knee abduction than both the SLS and LSD. The SLS generated the greatest amount of sagittal plane motion at the trunk, pelvis, and hip for the entirety of the movement. The LSD elicited the least amount of ipsilateral trunk lean. Thus, the FSD may be optimal for assessing frontal plane knee motion as a screen for injury risk, while the SLS provided greater demand on the sagittal plane motion resulting in increased demand of the hip musculature.
The purpose of the second manuscript was to examine the ability of each task to elicit bilateral differences at the group and individual level. Kinematic waveforms in the fontal and sagittal plane at the trunk, pelvis, hip, and knee were analyzed to compare bilateral differences elicited during each task. Participants self-identified their preferred (perceived as most stable) and non-preferred legs for each task. Minimal differences occurred at the group level when comparing preferred and non-preferred legs during the FSD, LSD, and SLS. Performing the LSD on the non-preferred leg resulted in increased pelvic drop at the group level. There were no other significant group findings for the LSD, FSD, or SLS. At individual level, numerous differences were identified with the largest percentage of participants demonstrating asymmetries for frontal plane knee motion. Sagittal plane asymmetries were most common at the pelvis during the FSD. Individual analyses were necessary to illustrate the prevalence of asymmetrical movement patterns across tasks and participants.
The primary purpose of the final manuscript was to examine whether self-identified Total Motion Release® (TMR®) scores coincided with mechanical asymmetries during a SLS. The secondary purpose was to explore whether improving the subjective self-reported imbalances resulted in decreased movement pattern asymmetries. Sagittal plane mechanical waveforms for the SLS task were used to evaluate group and individual mechanical bilateral differences before and after the TMR® intervention. The study population included individuals who had bilateral difference scores greater than 10 on 0–100-point TMR® scale, with higher scores indicating a greater difference between legs. The leg that scored higher was classified as the non-preferred leg. When preferred leg was identified based on task specific criteria, reduced knee flexion, ankle flexion, and internal knee flexion moments were identified on the non-preferred leg for both group and individual analyses. After the intervention, subjective scores for dysfunction had equalized between legs. Additionally, participants had increased their internal knee flexion moments on the non-preferred leg. Bilateral differences for knee and ankle flexion, as well as knee flexion moments persisted following the intervention. In conclusion, practitioners should consider the potential of the TMR® protocol to improve self-perceived scores of dysfunction during a SLS; however, objective measures of movement should also be included when rehabilitative protocols intend to address mechanical imbalances.
The overall results of this dissertation indicate: 1) single leg movement tasks should not be used interchangeably, and the mechanical demands of each task may best suit specific screening or rehabilitative protocols, 2) incongruities between group and individual analyses indicated that it is necessary to include individual analyses when assessing movement pattern asymmetries, and 3) including objective measures of patient perceptions is required to dichotomize legs for group analyses. Future studies should begin to examine the importance of the observed movement asymmetries by considering individual analyses in conjunction with patient reported scales while performing longitudinal injury tracking.