The Associations between Asymmetries in Quadriceps Strength and Gait in Unilateral Transtibial Amputees

Background – Individuals with unilateral transtibial amputations (ITTAs) are asymmetrical in quadriceps strength. It is unknown if this is associated with gait performance characteristics such as walking speed and limb symmetry.
Research Question – Are quadriceps strength asymmetries related to walking speed and/ or gait asymmetries in ITTAs?
Methods – Knee-extensor isometric maximum voluntary torque (MVT) and rate of torque development (RTD) were measured in eight ITTAs. Gait data were captured as the ITTAs walked at self-selected habitual and fast speeds. Step length and single support time, peak knee extension moments and their impulse and peak vertical ground reaction force (vGRF) in the braking and propulsive phases of stance were extracted. Bilateral Asymmetry Index (BAI) and, for gait variables only, difference in BAI between walking speeds (ΔBAI) were calculated. Correlation analyses assessed the relationships between MVT and RTD asymmetry and (1) walking speed; (2) gait asymmetries.
Results – Associations between strength and gait BAIs generally became more apparent at faster walking speeds, and when the difference in BAI between fast and habitual walking speed was considered. BAI RTD was strongly negatively correlated with habitual and fast walking speeds (r=~0.83). Larger BAI RTD was strongly correlated with propulsive vGRF BAI in fast walking, and larger ΔBAIs in vGRF during both the braking and propulsion phases of gait (r=0.74–0.92). ITTAs who exhibited greater BAI MVT showed greater ΔBAI in single support time (r=0.83).
Significance – While MVT and RTD BAI appear to be associated with gait asymmetries in ITTAs, the magnitude of the asymmetry in RTD appears to be a more sensitive marker of walking speed. Based on these results, it’s possible that strengthening the knee-extensors of the amputated limb to improve both MVT and RTD symmetry may benefit walking speed, and reduce asymmetrical loading in gait.