The Role of Low Back Capacities on Loaded and Unloaded Functional Movements: Squat and Lunge

Abstract

Variability of movement patterns across individuals have been well documented in healthy young adults. Large heterogeneity of movement patterns within seemingly homogenous populations suggests the possible presence of subgrouping of individuals. This variability makes it difficult to study and draw conclusions based on group effects, since group means may not be representative of individuals within the group, and especially when subgroups respond differently to interventions. It is also well established that certain movements and movement characteristics are relevant to movement efficiency, tissue exposure, and injury risk, however, it is not fully understood why individuals utilize certain movement patterns over others. It is plausible that physical capacity related differences between subgroups of individuals can help explain differences in movement. As such, this thesis aimed to cluster individuals according to their lumbar movement profiles during functional movements, and then relate characteristic profiles of each subgroup to the low back capacities of strength, muscular endurance, proprioception, and motor control. Additionally, this thesis investigated the effects of introducing a moderate challenge (i.e., loading) to the lumbar movement profiles during functional movements. Thirty-two healthy young adults (16 M, 16 F) performed two sets of ten repetitions each of squat (SQT) and lunge (LNG) in both unloaded (UL) and loaded (LD) conditions. Additionally, lumbar capacity tests of strength (S), endurance (E), joint position accuracy (P-A), joint position sensitivity (P-S), and motor control (MC) were assessed. State spaces of lumbar angle dynamics for each condition of movement were constructed, then discretized into 48 bins and averaged across repetitions. State spaces were then analyzed using spectral clustering with the number of subgroups selected based on the strongest silhouette score. Analyses of variance (ANOVAs) testing the effect of sex and group on each capacity test’s scores were conducted. The results of the clustering produced two groups with weak clustering strength in each condition. In both the SQT UL and SQT LD conditions, a significant interaction between sex and group in P-S (p = 0.01), and a significant effect of sex in E (p = 0.04)were found. In the LNG UL condition, a significant interaction between sex and group in P-A (p = 0.04), and a significant effect of sex in E (p = 0.04) were found. Significant interactions between group and sex were found in both P-S (p = 0.04) and MC (p = 0.03) for the LNG LD condition. Differences in lumbar capacities between groups were related to features of the state spaces, including shape, diffuseness, and intensity of attractors. This thesis highlighted the importance of physical capacities on movement patterns and affirmed the necessity of characterizing subgroups of individuals within a heterogeneous sample population. This thesis provides a framework for more comprehensive investigations into the relationships between specific capacities and movement profiles.