Ground Reaction Force Comparison Between Barefoot and Shod Single Leg Landing at Varied Heights

Background: Landing is a common movement that occurs in many sports. Barefoot research has gained popularity in examining how shoes alter natural movements. However, it is unknown how a single leg landing under barefoot conditions, as well as landing height, affects ground reaction forces (GRF). Objective: The purpose of this research was to examine the differences in GRF during a single leg landing under barefoot and shod conditions from various heights. Methods: Sixteen female Division II collegiate athletes, 8 basketball (age: 19.88 ± 0.64 yrs; height: 1.77 ± 0.09 m; mass: 75.76 ± 12.97 kg) and 8 volleyball (age: 20.00 ± 1.07 yrs; height: 1.74 ± 0.08 m; mass: 72.41 ± 5.41 kg), performed single leg landings from 12, 18, 24, and 30 inches barefoot and shod. An AMTI AccuGait force plate was used to record GRF. A 2 (condition) x 4 (box height) x 2 (sport) repeated measures ANOVA was performed to determine any GRF differences. Results: There were no significant three way or two-way interactions (p 0.05). There was also no main effect for sport (p 0.05). There were main effects for footwear and box height (p = 0.000) where shod (2295.121 ± 66.025 N) had greater impact than barefoot (2090.233 ± 62.684 N). Conclusions: Single leg barefoot landings resulted in less vertical GRF than shod landings. This could be due to increased flexion at the joints which aids in force absorption

The Effects of Surface Composition on 6-weeks of Plyometric Training

Background: Plyometric training programs may be performed on a hard surface or a soft surface to target specific training adaptations and enhance jump performance. However, it is unknown how surface compliance impacts jump performance. Objective: To compare changes in horizontal lower body power following a 6-week plyometric training program performed on a soft surface (n = 9) and a hard surface (n = 11). Methods: This was a quasi-experimental study. University students (N = 20; males = 11, females = 9; age: 20.4 ± 3.7 yr; body mass: 68.4 ± 12.5 kg; height 1.7 ± 0.1 m) with a history of being physically active volunteered to participate. Participants performed an initial pre-test standing long jump (SLJ), measured in centimeters (cm), then went through an accommodation period to be familiarized with training demands. A post-accommodation pre-test for SLJ was then completed. After the accommodation period, a 6-week plyometric training program was conducted. Following the completion of the training, a post-test was performed. The SLJ distance was analyzed with a 2 (surface) x 2 (time) repeated measures ANOVA. Results: There was no interaction for surface, but there was a main effect for time. Both training groups improved jump distance from pre- (soft surface = 191.6 ± 34.6 cm, hard surface = 216.1 ± 25.4 cm) to post-test (soft surface = 205.7 ± 38.8 cm, hard surface = 227.2 ± 23.4 cm). Conclusion: Practitioners designing plyometric training programs to increase lower body horizontal power may perform the training sessions on a soft surface or a hard surface and see similar improvements in horizontal jump performance

Effects of Drop Height on Drop Jump Performance

Background: Drop jumps (DJ) are commonly implemented in plyometric training programs in an attempt to enhance jump performance. However, it is unknown how different drop heights (DH) affect reactive strength index (RSI), jump height (JH) and ground contact time (GCT). Objectives: The purpose of this study was to assess the effect of various DHs on RSI, JH, and GCT. Methods: Twenty volunteers with a history of plyometric training (Males = 13, Females = 7; age: 22.80 ± 2.69 yr, height: 175.65 ± 11.81 cm, mass: 78.32 ± 13.50 kg) performed DJs from 30 cm (DJ30), 45 cm (DJ45), 60 cm (DJ60), 76 cm (DJ76), and 91 cm (DJ91) and a countermovement jump (0 cm). A 16-camera Vicon system was used to track reflective markers to calculate JH; a Kistler force plate was used to record GCT. RSI was calculated by dividing JH by GCT. RSI and GCT were compared using a 2x5 (sex x DH) mixed factor repeated measures ANOVA, while JH was compared using a 2x6 (sex x DH) repeated measures ANOVA. Results: There were no interactions, but there was a main effect for sex for both JH (M>F) and GCT (F>M). JH demonstrated no main effect for DH: DJ30 (0.49 ± 0.11 m), DJ45 (0.50 ± 0.11 m), DJ60 (0.49 ± 0.12 m), DJ76 (0.50 ± 0.11 m), and DJ91 (0.48 ± 0.12 m). However, GCT showed a main effect where DJ30 (0.36 ± 0.10 s), DJ45 (0.36 ± 0.12 s), and DJ60 (0.37 ± 0.10 s) were not significantly different but were less than DJ76 (0.40 ± 0.12 s) and DJ91 (0.42 ± 0.12 s). Conclusions: Increasing DH beyond 60 cm increased GCT but did not affect JH, resulting in decreased RSI. Therefore, practitioners designing plyometric training programs that implement DJs may utilize DHs up to 60 cm, thereby minimizing GCT without compromising JH