Landing ground reaction forces in figure skaters and non-skaters

Abstract

Researchers and clinicians have suggested that overuse injuries to the lower back and lower extremities of figure skaters may be associated with the repeated high impact forces sustained during jump landings. Our primary aim was to compare the vertical ground reaction forces (GRFs) in freestyle figure skaters (n = 26) and non-skaters (n = 18) for the same barefoot single leg landing on a force plate from a 20 cm platform. Compared with non-skaters, skaters exhibited a significantly greater normalised peak GRF (3.50 ± 0.47 × body weight for skaters vs. 3.13 ± 0.45 × body weight for non-skaters), significantly shorter time to peak GRF (81.21 ± 14.01 ms for skaters vs. 93.81 ± 16.49 ms for non-skaters), and significantly longer time to stabilisation (TTS) of the GRF (2.38 ± 0.07 s for skaters vs. 2.22 ± 0.07 s for non-skaters). Skaters also confined their centre of pressure (CoP) to a significantly smaller mediolateral (M–L) (25%) and anterior–posterior (A–P) (40%) range during the landing phase, with the position of the CoP located in the mid to forefoot region. The narrower and more forward position of the CoP in skaters may at least partially explain the greater peak GRF, shorter time to peak, and longer TTS. Training and/or equipment modification serve as potential targets to decrease peak GRF by distributing it over a longer time period. More comprehensive studies including electromyography and motion capture are needed to fully characterise the unique figure skater landing strategy.     

Shoe collar height and heel counter-stiffness for shoe cushioning and joint stability in landing

ABSTRACT

This study examined the effects of shoe collar-height and counter-stiffness on ground reaction force (GRF), ankle and knee mechanics in landing. Eighteen university basketball players performed drop landing when wearing shoes in different collar height (high vs. low) and counter-stiffness (stiffer vs. less stiff). Biomechanical variables were measured with force platform and motion capturing systems. Two-way repeated measures ANOVA was performed with α = 0.05. Wearing high collar shoes exhibited smaller peak ankle dorsiflexion and total sagittal RoM, peak knee extension moment, but larger peak knee varus moment than the low collar shoes. Stiffer counter-stiffness shoes related to smaller ankle inversion at touchdown and total coronal RoM, but larger peak knee flexion and increased total ankle and knee sagittal RoM than the less stiff counter-stiffness. Furthermore, wearing stiffer counter-stiffness shoes increased forefoot GRF peak at high collar condition, while no significant differences between counter-stiffness at low collar condition. These results suggest that although higher collar height and/or stiffness heel counter used can reduce ankle motion in coronal plane, it would increase the motion and loading at knee joint, which is susceptible to knee injuries. These findings could be insightful for training and footwear development in basketball.     

Between-limb asymmetry in kinetic and temporal characteristics during bilateral plyometric drop jumps from different heights

ABSTRACT

This study investigated the between-limb asymmetry in kinetic and temporal characteristics during bilateral plyometric drop jumps from different heights. Seventeen male basketball players performed drop jumps from 3 heights on two platforms in randomized orders. Vertical ground reaction force data were analysed with respect to the lead limb (i.e. the limb stepping off the raised platform first) and trail limb. Peak forces and loading rates of each limb were calculated. The absolute time differential between the two limbs at initial ground contact and takeoff were determined. The frequency of symmetrical landing and taking off with “both limbs together” were counted using 3 time windows. Results showed that the lead limb displayed higher peak forces and loading rates than the trail limb across all heights (p <.05). As drop height increased, the absolute time differentials decreased at initial ground contact (p <.001) but increased at takeoff (p =.035). The greater the preset time window, the more landings and takeoffs were classified as bilaterally symmetrical. In conclusion, higher drop heights allowed subjects to become more bilaterally symmetrical in the timing of landing but this reduction in temporal asymmetry did not accompany with any reduction in kinetic asymmetry.     

田径、举重运动员下肢反应力量能力探析

采用国际上通用的反应力量测试手段和方法，对191名田径、举重运动员和普通人进行了实验测试，通过对测试结果的统计分析，发现：（1）田径、举重运动员下肢反应力量测试结果未能表现出运动项目和竞技水平间的显著性差异；（2）跳深实验中，适宜的下落高度随着性别、运动项目、竞技水平等条件的不同，差异较大，因此，判定适宜的下落高度时，最好具体分析，因人而异；（3）起跳时间对于判定适宜的下落高度也有一定影响，准确的适宜下落高度的判定，对于反应力量的训练具有重要意义。