The purpose of this study was to determine the relationship between joint moments in functional movement and joint moments in isokinetic testing. Isokinetic testing was performed in order to quantify the maximal knee moments that subjects could create under isokinetic (open kinetic chain) conditions. Kinematic and kinetic data were collected using a video-based camera analysis and a force platform, as subjects ascended a stair while carrying increasing loads. The relative contributions of the ankle, knee, and hip moments required to perform this functional task (a closed kinetic chain task) at each load level were compared to the maximum moments created during isokinetic testing. Clarification of the relationship between the joint moments required for functional movement and the joint moments measured during isokinetic testing may allow for predictions of functional capacity based on isokinetic strength testing. Preliminary data collected from two able-bodied subjects revealed significant differences in the kinetic strategies used to perform stair ascent. The contribution of the knee extensors to the functional task of stair ascent (with no additional load) was 27% greater in one subject (subject A) as compared to the other (subject B). The knee extensor contribution to the support moment in subject A decreased as loads increased, while subject B had a constant contribution to the total support moment from the knee extensor. This difference in kinetic strategy was related to a significant difference in knee extensor strength (peak moment of 2.11 N.m/kg in subject A versus 1.76 N.m/kg in subject B, as measured by an isokinetic dynamometer). This suggests that lower extremity strength distribution may predict the kinetic strategy used to perform a functional task.
