Differences in spring-mass characteristics between one- and two-legged hopping

Although many athletic activities and plyometric training methods involve both unilateral and bilateral movement, little is known about differences in the leg stiffness (K(leg)) experienced during one-legged hopping (OLH) and two-legged hopping (TLH) in place. The purpose of this study was to investigate the effect of hopping frequencies on differences in K(leg) during OLH and TLH. Using a spring-mass model and data collected from 17 participants during OLH and TLH at frequencies of 2.0, 2.5, and 3.0 Hz, K(leg) was calculated as the ratio of maximal ground reaction force (F(peak)) to the maximum center of mass displacement (ΔCOM) at the middle of the stance phase measured from vertical ground reaction force. Both K(leg) and F(peak) were found to be significantly greater during TLH than OLH at all frequencies, but type of hopping was not found to have a significant effect on ΔCOM. These results suggest that K(leg) is different between OLH and TLH at a given hopping frequency and differences in K(leg) during OLH and TLH are mainly associated with differences in F(peak) but not ΔCOM.