Landing from a jump or elevated surface is a common mechanism of injury. Contrasting lower extremity adjustments in response to landing height alterations may highlight factors related to injury.
PURPOSE: The purpose of the study was to examine changes in lower extremity sagittal joint moment variability following landing height manipulations. Joint-specific adjustments were investigated via principal component analysis (PCA).
METHODS: Ten healthy volunteers (4M, 6F; 21.5±2.3y, 1.71±0.12m, 66.3±11.7kg) provided institutionally approved consent prior to participation. Subjects completed 5 landing trials from 3 heights, computed as percentages of maximum vertical jump height (60%, 100%, 140% MVJH). Data were acquired using dual force platform (Kistler 9281CA, 9281B; 2000Hz) and 12-camera motion capture systems (Vicon MX-T40S; 200Hz). Sagittal internal joint moments (hip, knee, ankle) were normalized to body mass (Nm/kg) and temporally normalized (101 data points) from ground contact to the point vertical center of mass velocity reached zero. Separate analyses were performed at the hip, knee, and ankle joints, extracting principal components (PCs) providing 95% cumulative explained variance. One-way ANOVAs and pairwise comparisons identified PCs demonstrating differences among landing condition PC scores (α=0.05; Bonferroni post-hoc adjustments). PC loading vectors were visually examined for sources of variation captured by each PC that showed differences among conditions.
RESULTS: The number of extracted PCs identified a proximal to distal decrease among joints (hip: 8 PCs, knee: 6 PCs, ankle: 4 PCs). Differences among landing height PC scores were detected in PC1 at the hip (140% > 60%) and PC2 at the knee and ankle joints (140% & 100% > 60%; p<.05). At the hip, PC1 loading vector identified a peak flexor moment from 0-10% of landing and peak extensor moment from 10-30% of landing. At the knee, PC2 loading vector identified bimodal extensor moments from 0-10% and 10-40% of landing, while PC2 loading vector at the ankle captured a peak plantarflexor moment from 0-30% of landing.
CONCLUSIONS: Joint-specific adjustments were observed across landing heights. The availability of contrasting motor solutions expressed via PCA may highlight important considerations for factors related to landing injuries.
