Implementation of a two-dimensional biomechanical model i n an opto-electronic motion analysis system

The objective of this study was to implement a dynamic, two-dimensional biomechanical model, a force plate, and electromyography in a three-dimensional, opto-electronic motion analysis system. Further objectives were to present kinematic and kinetic data for basic movements used in rehabilitation and athletic testing, and to make the system rapid and adaptable for clinical use. Kinematic data, including joint movements and muscle length changes, as well as kinetic data, including net torque and net power output, are presented for the ankle, knee and hip joints when performing two-legged vertical counter-movement jumps, walking, and one-leg long hops. Coefficients of variation for net torque and the net power output were between 1.6% and 18·1% when analysing the countermovement jumps, and there were similar results for walking. When performing the hop, the coefficients of variation for net torques were all less than 16%, but power output values were unequivocally non-satisfactory (30% maximum). In conclusion, reliability was acceptable for the counter-movement jumps and for the analysis of walking, but power output reliability for the hops at touch-down was found to be poor, probably due to soft tissue and marker movement relative to the underlying bone. The moderate amount of time needed for testing makes the system useful for clinical practice.