During step descent, older adults exhibit decreased knee range of motion and increased vastus lateralis muscle activity.

Purpose: There is substantial evidence indicating an increase in the incidence of lower limb joint osteoarthritis with increasing age. One factor that may contribute to this is an age related reduction in the ability to attenuate the impulse generated during gait and step descent.

Scope: The aim of this study was to investigate the differences between older and younger adults, in the strategies used to attenuate the force generated between initial contact (IC) and maximum vertical ground reaction force (vGRF) (impulse phase) when descending a step.

Methods: Ten older participants aged 60-80 years (mean 65.3, SD ±5) and 10 younger participants aged 20-30 years (mean 22.8, SD ±2.5) took part in the study. Vertical ground reaction force (vGRF) and the time taken to reach maximum vGRF were measured. The maximum joint range of motion of the hip and knee during step descent was measured between IC and the maximum vGRF. Electromyography (EMG) was measured from four lower limb muscles and normalised to task for each individual.

Results: There was a statistically significant difference between older and younger adults in the amount of knee flexion and vastus lateralis EMG activity in the leading leg during the impulse phase of step descent. Older adults had less knee flexion (F(1,18)=5.48; p=0.031) and more vastus lateralis EMG activity (F(1,18)=5.21; p=0.035) during step descent than younger adults.

Conclusion: Older and younger adults used different strategies during step descent. Older adults demonstrated two strategies that have the potential to increase the impulse of a step.