Determination of hydrodynamic drag forces and drag coefficients on human leg/foot model during knee exercise

Objective. The purpose of this laboratory experiment was to measure hydrodynamic drag forces in barefoot/hydro-boot conditions and accordingly, to determine the coefficients of drag on human leg/foot model during simulated knee extension–flexion exercise. Design. The prosthesis of the human lower leg was set in a water tank and connected into an isokinetic force dynamometer to measure resistive forces during knee motion. Background. Quantifying resistance for aquatic exercises has been a challenge in hydrotherapy. The use of models of foot/leg provides a practical method to calculate coefficients of drag and to estimate resistance for rehabilitation purposes in musculoskeletal and amputee patients. Methods. The dynamometer produced constant angular velocities of 250°/s, 270°/s and 300°/s to the prosthesis. The baseline for measurements was performed in barefoot condition. A hydro-boot was used to study effects of increased frontal area (30%) of the leg on drag forces and coefficients. Results. The maximal drag force values were 61 N (300°/s) in barefoot and 270 N (270°/s) in hydro-boot condition. Related drag coefficient values during the range of motion were from 0.3 to 0.1 and from 1 to 0.8, respectively. Conclusions. Drag force and related drag coefficient were highest during the early part of extension (150–140° flexion) as the model was opposing the lift forces with the influence of water resistance. The effect of velocity was remarkable on drag forces but minimal on drag coefficient values.