An approach to estimating performance capacity envelopes: knee extensor system example

Develops and evaluates an approach to modeling multi-dimensional (strength, joint angle and speed) performance capacity envelopes that more completely characterize specific human musculoskeletal subsystems (e.g. trunk extensor and wrist extensor). This is a logical extension to the typical 2D families of curves produced by isokinetic measures, which provide only limited utility. Isometric and newly modified isokinetic protocols were used to obtain a parametric data set for each of the 21 (male and female) volunteers, using the knee extensor as a representative subsystem for the approach. The functional form of a normalized 3D performance capacity envelope representing the general population was determined using statistical analysis of the subject data. A limited subset of each subject's data was used in combination with the general population model to derive higher-fidelity subject-specific models. The estimated knee extensor torque capacity of each model was compared to the measured torque values. The approach provided torque capacity estimates that were comparable to the test-retest accuracy.