Inter-individual differences in the passive resistance of the human knee

The passive resistance of the knee to angular motion in the flexion-extension plane was investigated in groups of healthy males (n = 29) and females (n = 20). ‘Least square’ fitting procedures proved to be reliable for approximating the equilibrium angle of the knee and variables of the moment/angle diagrams. To assess the influence of the dimensions of the lower limb on the resistance of the knee, a multiple regression analysis was performed, using seven dimensional parameters of the lower limb. The results indicate that for males 35–77% (mean 58%) of the total variance is accounted for by the dimensional parameters. For females this range is 9–74% (mean 44%). Differences between males and females exist in all selected resistance variables. To decrease the influence of dimensional parameters, the slopes of the exponential curves relating moment and knee angle are expressed as percentages of the absolute moment values. When the values of these ‘relative slopes’ are used, differences between males and females become less in flexion and are absent when the knee is extended. These results indicate that male-female differences can partly be ascribed to differences in dimensions.