Lower Extremity Kinematics are Different When Landing from a Box vs. Landing from a Countermovement Jump

Abstract

Many people get injured when landing from a jump. This has led researchers to study the mechanics of landing. It is common to control for the height of landing by having subjects step off a box onto a force platform to make sure study participants land from a known height. Whether or not this step-off (SO) landing technique simulates landing from a countermovement vertical jump (CMJ) is unknown. Previously we found ground reaction forces and force rates to be significantly different between SO and CMJ landings, at least in male subjects. Joint kinematics, however, were not reported in our previous study. PURPOSE: To compare lower extremity kinematics for SO landings vs. CMJ landings. METHODS: Eighteen subjects (9 males, 9 females) performed both maximal effort CMJ and SO landings on a force platform. The height of the SO box was adjusted so as to produce the same velocity at impact for each subject as their CMJ produced. Digitized coordinates of the hip, knee, and ankle joints were used to calculate joint angles. A mixed design two-way ANO VA with repeated measures (landing type x gender) with type as the between subjects factor was used to analyze the joint angles at initial ground contact and at peak ground reaction force. RESULTS: No significant differences in hip, knee, and ankle joint angles were observed between landing types at initial contact with F (1,16) = 0.36, P> 0.05, F (1,16) = 0.55, P>0.05, and F (1,16) = 0.10, P> 0.05, respectively. However, there were significant differences in hip, knee, and ankle joint angles at peak ground reaction force with F (1,16) = 8.52, p = 0.01, F (1,16) = 12.43, p = 0.003, and F (1,16) = 17.48, p = 0.001, respectively. No, gender by type interaction was seen for any of these comparisons. In addition, it was noticed that the equivalent landing heights when stepping off a box were on the average 0.10m lower than the actual box height as participants tended to lower their foot, thus lowering the body center of mass prior to becoming airborne. CONCLUSION: Results from this study suggest that hip, knee, and ankle kinematics are different when landing from a CMJ vs. SO. These results are consistent with our previous study that found ground reaction force differences. Thus, in order to properly study landing mechanics a true countermovement jump should be used and not stepping off a box.