Force-velocity relationship of leg muscles assessed with motorized treadmill tests: Two-velocity method.

Linear regression models applied on force (F) and velocity (V) data obtained from loaded multi-joint functional movement tasks have often been used to assess mechanical capacities of the tested muscles. The present study aimed to explore the properties of the F-V relationship of leg muscles exerting the maximum pulling F at a wide range of V on a standard motorized treadmill. Young and physically active male and female subjects (N=13+15) were tested on their maximum pulling F exerted horizontally while walking or running on a treadmill set to 8 different velocities (1.4-3.3m/s). Both the individual (median R=0.935) and averaged across the subjects F-V relationships (R=0.994) proved to be approximately linear and exceptionally strong, while their parameters depicting the leg muscle capacities for producing maximum F, V, and power (P; proportional to the product of F and V) were highly reliable (0.84<ICC<0.97). In addition, the same F-V relationship parameters obtained from only the highest and lowest treadmill V (i.e., the 'two-velocity method') revealed a strong relationship (0.89<R<0.99), and there were no meaningful differences regarding the magnitudes of the same parameters obtained from all 8 V's of the treadmill. We conclude that the F-V relationship of leg muscles tested through a wide range of treadmill V could be strong, linear, and reliable. Moreover, the relatively quick and fatigue-free two-velocity method could provide reliable and ecologically valid indices of F, V, and P producing capacities of leg muscles and, therefore, should be considered for future routine testing.