Joint moments have greater impact on vertical jump height than joint angular velocities

IntroductionThe ability to maximally accelerate one’s body from rest or after a preceding countermovement is a critical limitation in athletic performance (e.g. vertical jumping). To accelerate the body’s COM during a vertical jump, the hip, knee, and ankle joint must generate a high mechanical power. Since joint mechanical power is the product of joint moment and joint angular velocity, a given power output can be achieved by different relative contributions of those two components. Good performers of the vertical jump show higher mechanical power at the hip, knee, and ankle joint than poor performers [1]. Moreover, it is valuable knowledge for athletic coaches if there are differences in the joint moments and joint angular velocities between good and poor performers.
MethodsAn ex-post-facto-experiment has been applied to the database of the German Research Centre of Elite Sport Cologne, which encompasses vertical jump performance diagnostics of young athletes in North-Rhine-Westphalia (10 infrared cameras, 120 Hz, Vicon Motion Systems, Oxford, UK; 2 force plates, 1080 Hz, Kistler Winterthur, Suisse; inverse two-dimensional model Alaska Dynamicus, Alaska, Chemnitz, Germany). For the analysis, the database was sorted by countermovement jump height resulting in a group of good (0.35 - 0.40 m jump height, n = 52, male, 17.4 ± 3.5 yrs., 70.2 ± 12 kg) and a group of poor (0.20 – 0.25 m jump height, n = 52, male, 14.4 ± 1.4 yrs., 60.0 ± 11.7 kg) performers. The group differences in the time series of hip, knee, and ankle joint moments and angular velocities were investigated by using statistical parametric mapping.
Results and DiscussionDuring the negative phase of the CMJ there is no difference in the angular velocities between poor and good, whereas during the positive phase, the good group shows sig. greater peak angular velocities at the knee (105.1 ± 12.3°/s, p < 0.001) and ankle joint (99.4 ± 14.9 °/s, p < 0.01) than the poor group (93.3 ± 13.6 °/s, 87.3 ± 17.6 °/s). Regarding the external joint flexion moments, a sig. difference between the two groups was found for all joints. The joint moments of the good group were sig. higher at the hip (1.9 ± 0.4 Nm/kg vs. 1.4 ± 0.3 Nm/kg, p < 0.001), knee (1.1 ± 0.2 Nm/kg vs. 0.9 ± 0.2 Nm/kg, p < 0.001) and ankle joint (1.5 ± 0.2 Nm/kg vs. 1.2 ± 0.1 Nm/kg, p < 0.001) than those of the poor group. Additionally, the effect sizes of the differences in joint moments were larger than the effect sizes of the differences in angular velocities (hip: d = 1.7 (0.3), knee: d = 1.0 (0.8), ankle: d = 2.1 (0.7)), which indicates that the ability to generate higher joint moments might be more crucial in the performance of vertically directed ballistic movements than joint angular velocities. The difference in hip moments was present for the longest time during the jump phase (58-94 %), which confirms the importance of this joint also found by [2]. Interestingly, the higher hip moments did not lead to a significant increase in hip angular velocity, which implies a proximal to distal energy transfer through biarticular muscles [3].
ConclusionsTheses findings suggest that athletic training should focus on provoking high joint moments rather than high angular velocities to improve vertical jump height.
References[1] Lees & Vanezis (2007). SLE Conference, 19-21.[2] Lees et al. (2004). J Strength Cond Res, 18(4), 787–791.[3] Jacobs et al. (1996). J Biomech, 29(4), 513–523.