Search

Musculoskeletal injuries often occur during the execution of dynamic sporting tasks that involve rotation. The prescription of appropriate prevention strategies of musculoskeletal injury relies on assessments to identify risk, but current assessment tools focus on uniplanar movements. The purpose of this paper is to demonstrate the utility of the unilateral 180° jump as a potential assessment tool for injury risk in the lower body by (1) providing descriptive kinematics of the knee, thigh, and pelvis (2) conducting inter-segmental coordination analysis, and (3) comparing the knee kinematics between the dominant and non-dominant limb (NDL) during the loading (LOP) and landing phase (LAP). Elite rugby players completed one session, performing five 180° unilateral jumps on each limb while collecting kinematic data. Independent t-tests were used to compare peak angles of DL and NDL. Continuous Relative Phase (CRP) plots were constructed for thorax and pelvis in the transverse plane. At the loading phase, the non-dominant limb had greater peak knee abduction (ABD) (p = 0.01). At the landing phase, the dominant limb had greater peak knee adduction (ADD) (p = 0.05). At the landing phase, the non-dominant limb had greater peak knee ABD (p = 0.01). CRP plots indicate participants can utilize a thorax-led, pelvis-led, or synchronized rotational method. Bilateral asymmetries were observed, indicated by significant differences in the bilateral landing phase peak ADD/ABD, which is of particular interest considering all participants were healthy. Therefore, additional research is needed to determine thresholds for injury risk during rotational tasks.

The purpose of this study was to investigate the eccentric and concentric force-velocity (Fv) characteristics recorded during drop jumps (DJ) from different heights and loaded jump squats (JS) and to determine the number of jumps required to accurately model the eccentric and concentric Fv relationships. Fourteen resistance-trained men (age: 21.9 ± 1.8 years) performed a countermovement jump (CMJ) and DJ from heights of 0.40, 0.60, and 0.80 m. JS with loads equivalent to 0%, 27%, 56%, and 85% 1-repetition maximum were performed in a separate session. Force platforms and a 3-D motion analysis system were used to record the average force ( F ¯ ) and velocity ( v ¯ ) during the absorption (CMJ, DJ40, DJ60, DJ80) and propulsion (JS0, JS27, JS56, JS85) phases of the jumps. Eccentric (absorption phase) and concentric (propulsion phase) Fv characteristics were then calculated and linear regression equations were determined when the number of jumps included was varied. F ¯ during the absorption phase significantly increased from CMJ to DJ60 while v ¯ increased significantly from CMJ to DJ80. The two-point method (CMJ, DJ80) resulted in a significantly lower y-intercept (mean difference [MD]: 0.7 N/kg) and a greater slope (MD: 0.7 Ns/m) for the eccentric Fv characteristics compared to the multiple-point method. F ¯ increased significantly and v ¯ decreased significantly with increasing external load in the JS conditions. The two-point method (JS0, JS85) resulted in a significantly greater y-intercept (MD: 1.1 N/kg) compared to the multiple-point method for the concentric Fv characteristics. Both DJ and loaded JS may provide means of assessing the eccentric and concentric Fv characteristics with only two jumps being required.

The purpose of this study was to compare different methods for assessing plyometric ability during countermovement (CMJ) and drop jumps (DJ) in a group of adults and adolescents. Ten resistance-trained adult men (age: 22.6 ± 1.6 years) and ten adolescent male basketball players (age: 16.5 ± 0.7 years) performed a CMJ and a DJ from a height of 0.40 m. Jump height (JH), contact time, normalized work (WNORM), and power output (PONORM) during the absorption and propulsion phases were calculated from force platforms and 3-D motion analysis data. Plyometric ability was assessed using the modified reactive strength index (RSIMOD during CMJ) and the reactive strength index (RSI during DJ) as well as three indices using propulsion time, propulsion work (PWI), and propulsion power. Adults jumped significantly higher than adolescents (mean difference [MD]: 0.05 m) while JH (MD: 0.05 m) and ground contact time (MD: 0.29 s) decreased significantly from CMJ to DJ. WNORM (MD: 4.2 J/kg) and PONORM (MD: 24.2 W/kg) during the absorption phase of CMJ were significantly less than these variables during the propulsion phases of the jumps. The reactive strength index variants increased significantly from the CMJ to DJ (MD: 0.23) while all other plyometric indices decreased significantly. Neither RSIMOD nor RSI contributed significantly to the prediction of JH during CMJ and DJ, respectively, while PWI was able to explain ≥68% of the variance in JH. Variants of the reactive strength index do not reflect the changes in mechanical variables during the ground contact phase of CMJ and DJ and may not provide an accurate assessment of plyometric ability during different vertical jumps.

Whole-body vibration (WBV) may positively influence performance acutely through the potentiation of the muscle's series elastic components and neuromuscular mechanisms. The purpose of this investigation was to examine the acute effects of WBV on sprint performance in NCAA Division I collegiate male sprinters and jumpers. Twenty-one athletes (n=21) completed a control or WBV protocol (30 seconds, 50 Hz, low amplitude ~3mm) one minute before a 30 m flying sprint. Each athlete participated in three separate trials using randomized treatment sessions (1 treatment per session) over 12 weeks of preparation training prior to the indoor season. The control condition consisted of no vibration, while treatment 1 (T1) and treatment 1 repeated (T1-R) incorporated vibration. The vibration-sprint protocol was repeated after a five minute rest period following the first sprint (test-re-test ICC≥0.81). The sprint consisted of a 15 m run-in from a standing start and a 30 m flying sprint with a total distance of 45 m. A two-way factorial ANOVA with repeated measures (p ≤ 0.05) was used to compare treatments. Statistics showed no differences between the treatments at all distances (average sprint time of control vs. T1, control vs. T1-R, and T1 vs. T1-R). The results of this study indicate that WBV at 50 Hz and low amplitude has no potentiation effect on sprint times (15, 30, 45, or 30 m fly). Further research is needed to determine if different WBV protocols may elicit enhanced results in 30 m flying sprint performance. The present WBV protocol does not appear to have practical acute value for sprinting. [ABSTRACT FROM AUTHOR]