The functional demand (FD) placed on the knee and hip of older adults during everyday activities

Age-related decline in physical capacity and diminishing physiological reserves may increase the demand placed on lower extremity joints during everyday activities. This study aimed to characterize the FD at the knee and hip joints of older adults during various mobility activities. Eighty-four healthy participants (60-88 years) performed strength tests using a custom-built dynamometer. Biomechanical assessment of gait, chair rise (CR) and sit-down (CSt), stair ascent (SA) and descent (SD) was performed using an 8-camera VICON system (120 Hz) and Kistler force plates. Comparisons between groups (60s, 70s and 80s) were made using ANOVA. The FD was defined as the muscle moment generated during a task, divided by the maximum isometric strength (expressed as a percentage). FD was higher in the 80s age group compared to those in the 60s. The demand on hip and knee extensors was normally higher than those of flexors across all the activities. The knee extensor demand during gait (101%), SA (103%) and SD (120%), and hip extensor demand during gait (127%) were high requiring moments in excess of the maximum isometric muscle strength available at these joints. FD during CR and CSt was comparatively lower with knee extensor demands of 73% and 69% and hip extensor demands of 88% and 51%, respectively. Gait, SA and SD placed high demands on the knee extensors while hip extensor demand was high for gait, CR, CSt and SA. The levels of demand leave little reserve capacity for the older adult to draw on in unexpected circumstances.