An EMG-to-Force Processing Method for Estimating In Vivo Knee Muscle Power During Self-Selected Speed Walking in Adults

The purpose of this study was to determine the power produced by knee muscles in normal adults when performing self-selected walking. The power of a single knee muscle is not directly measurable without invasive methods. An EMG-to-force processing (EFP) model was developed, which scaled muscle–tendon unit (MTU) power output to gait EMG. Positive power by each muscle occurred when force was developed during concentric contractions, and negative power occurred with lengthening contractions. The sum of EFP power produced by knee muscles was compared with the kinematics plus kinetics (KIN) knee power at percent gait cycle intervals. Closeness-of-fit of the EFP and KIN power curves (during active muscle forces) was used to validate the model. Key findings were that most knee muscles have a characteristic eccentric-then-concentric contraction pattern, and greatest power was produced by the Semimembranosis, with peak magnitude nearly matched by two vastus muscles (VL, VMO). The EMG-to-force processing approach provides reasonable estimates of active individual knee muscle power in self-selected speed walking in neurologically intact adults. Further, a prolonged period of the gait cycle showed substantial knee flexion or extension in the absence of power produced by muscles acting at the knee.