The influence of task type and movement speed on lower limb kinematics during single-leg tasks.

BACKGROUND

Single-leg squats and step-downs are commonly used to assess kinematic variables that may be linked to injuries. Task type and movement speed may influence the outcomes of interest because of different balance requirements.

RESEARCH QUESTION

What is the influence of task type and movement speed on lower limb kinematics?

METHODS

This is a cross-sectional within-subjects study where 22 physically active females performed three single-leg functional tasks (Squat, Anterior step-down, and Lateral step-down) at three movement speeds (slow [5 s], fast [2 s], and self-selected), while three-dimensional kinematic variables were recorded. Displacement values from the initial position in single-leg support until 60° or peak knee flexion were calculated. Two-way repeated measures ANOVA was used to compare tasks and speeds, and Cohen's d effect size (ES) was calculated for significant pairwise comparisons.

RESULTS

At 60°, lateral step-down presented the greatest hip adduction (large ES) and internal rotation (small ES). The anterior step-down had the lowest knee abduction displacement while the squat had the greatest (small to medium ES). At peak knee flexion, values increased but differences between tasks followed a similar pattern. Slow speed induced smaller displacement angles at the knee and hip (trivial to small ES).

SIGNIFICANCE

When knee abduction is the variable of interest, the SLS may be the best test since it elicits the greatest displacement, but when evaluating hip motion, SD might be best. Knee abduction and internal rotation were lowest in the slow condition, suggesting that faster speed may be more appropriate to detect abnormal movement patterns. However, the small difference in absolute values (i.e., degrees of movement) may indicate that the differences are not clinically significant, particularly for speed comparisons. Researchers and clinicians should take this into consideration when choosing the most appropriate task and the instruction to give during its execution.