Bilateral Differences in Lower-Extremity Biomechanics during Step-Close and No-Step Jumps

Due to the dynamic nature of many sports, the countermovement of a vertical jump is often initiated simultaneous with stepping into the jump location. This is often referred to as a step-close (SC) jump with a lead leg (LL) stepping in and a trail leg (TL) closing the stance. Since forces are at or near maximal towards the end of the countermovement, separate demands may be placed on each leg. There may also be differences compared to the no-step (NS) jump that could be important for training, performance, and injury prevention. PURPOSE: The goal of this investigation was to characterize the biomechanical differences of the lower extremities during a SC jump as well as compare to the NS jump. METHODS: Recreationally competitive volleyball players volunteered for the study (12 men and 12 women, age = 21.9+/−1.9 yrs, height = 175+/−8 cm, mass = 71.2+/−9.0 kg (Mean +/− SD)). Three maximal effort jumps in each condition, as measured by a double hand reach, were analyzed. Ground reaction forces were measured with two force platforms and lower-extremity kinematics with optical capture. Joint motion as well as net muscular moments and powers from inverse dynamics were analyzed in the anatomical flexion/extension plane of movement for the hip, knee, and ankle. Significance was assessed at p <0.05 for appropriate maximum, minimum, and average values during the propulsion phase (analysis began when the total vertical ground reaction force exceeded bodyweight towards the end of the countermovement). RESULTS: Subjects jumped higher in the SC condition (51+/−11 versus 48+/−11 cm). The hip, knee, and ankle of the TL were flexed/plantarflexed to a greater degree at the bottom of the countermovement compared to the LL in the SC jump. Maximum and average hip and knee extensor moments and average ankle plantarflexor moments were greater in the LL compared to the TL in the SC jump with only the maximum ankle power greater in the TL. Maximum and average extensor/plantarflexor moments of the LL were greater at all joints in the SC compared to NS jump. Maximum hip and ankle joint extensor/plantarflexor moments of the TL were greater in the SC compared to NS jump as was the maximum knee joint power while the average ankle joint extensor moment was reduced. CONCLUSIONS: Due to the increased demands placed on the LL and differences observed compared to the NS jump, strength and conditioning programs should be tailored to promote appropriate development and prevent injury. This includes activities, such as plyometric jumps, that incorporate a SC technique and the alternating of lead and trail legs between sets/repetitions to minimize the potential development of functional asymmetries.