The influence of squat depth on maximal vertical jump performance

Abstract

An increase in the period over which a muscle generates force can lead to the generation of greater force and, therefore, for example in jumping, to greater jump height. The aim of this study was to examine the effect of squat depth on maximum vertical jump performance. We hypothesized that jump height would increase with increasing depth of squat due to the greater time available for the generation of muscular force. Ten participants performed jumps from preferred and deep squat positions. A computer model simulated jumps from the different starting postures. The participants showed no difference in jump height in jumps from deep and preferred positions. Simulated jumps produced similar kinematics to the participants' jumps. The optimal squat depth for the simulated jumps was the lowest position the model was able to jump from. Because jumping from a deep squat is rarely practised, it is unlikely that these jumps were optimally coordinated by the participants. Differences in experimental vertical ground reaction force patterns also suggest that jumps from a deep squat are not optimally coordinated. These results suggest there is the potential for athletes to increase jump performance by exploiting a greater range of motion.     

The influence of squat depth on maximal vertical jump performance

An increase in the period over which a muscle generates force can lead to the generation of greater force and, therefore, for example in jumping, to greater jump height. The aim of this study was to examine the effect of squat depth on maximum vertical jump performance. We hypothesized that jump height would increase with increasing depth of squat due to the greater time available for the generation of muscular force. Ten participants performed jumps from preferred and deep squat positions. A computer model simulated jumps from the different starting postures. The participants showed no difference in jump height in jumps from deep and preferred positions. Simulated jumps produced similar kinematics to the participants' jumps. The optimal squat depth for the simulated jumps was the lowest position the model was able to jump from. Because jumping from a deep squat is rarely practised, it is unlikely that these jumps were optimally coordinated by the participants. Differences in experimental vertical ground reaction force patterns also suggest that jumps from a deep squat are not optimally coordinated. These results suggest there is the potential for athletes to increase jump performance by exploiting a greater range of motion.     

不同下肢力量训练形式对原地纵跳成绩的影响

本文通过文献资料珐、实验法和教理统计珐,以西安体育学院2010级20名休闲体育专业的学生为研究对象（A粗【单纯向心收缩】10人,B组【离心＋向心收缩】10人）,分别采用两种不同肌肉收缩形式进行为期8周的下肢力量训练。实验前后采用瑞士KILSTER9287C型三堆渊力台,对实验对象的静止纵跳、反弹从跳进行动力学分析。     

Effects of adding a preceding run-up on performance, blood lactate concentration and heart rate during maximal intermittent vertical jumping

In this study, we examined the effects of a prior run-up on intermittent maximal vertical jump performance. Seven regionally ranked male volleyball players volunteered to participate in the study. They performed three randomized tests: (1) six repeated intermittent maximal jumps (jump condition), (2) six repeated intermittent run-ups (run-up condition), and (3) six repeated run-ups followed by maximal jumps (run-up plus jump condition). All performances were assessed and blood lactate concentration and heart rate were measured before and after each of the tests. Mean ( +/- ) jump performance (64.7 +/- 2.3 cm) increased significantly (P = 0.02) over the course of the jump condition and was significantly higher (P < 0.001) than for the run-up plus jump condition (58.0 +/- 3.2 cm), which tended to decrease with repetition. Blood lactate concentration was significantly higher in the run-up plus jump condition (3.73 +/- 0.24 mmol . l(-1)) than in the jump (2.61 +/- 0.26 mmol . l(-1), P = 0.02) and run-up (2.86 +/- 0.18 mmol . l(-1), P = 0.03) conditions. The increase in heart rate was significantly higher both in the run-up plus jump condition (33 +/- 6 beats . min(-1), P = 0.05) and run-up condition (33 +/- 4 beats . min(-1), P = 0.02) than in the jump condition (21 +/- 3 beats . min(-1)). The results indicate that the addition of run-ups probably impeded performance in the repetition of vertical jumps.     

手臂摆动在跳高起跳中的生物力学意义

用模型研究法对跳高起跳中的手臂摆动进行了研究．分析了起跳前手臂和身体其余部分的受力情况．探讨了起跳时加速力的产生过程,比较了手臂不同的加速摆动方式对身体重心最后速度的影响。由此指出,手臂摆动对身体起跳加速力的贡献率很大,并且,手臂加速摆动的距离越长,身体重心速度的增加越明显。     

The effects of limb dominance and a short term,high intensity exercise protocol on both landings of the vertical drop jump: implications for the vertical drop jump as a screening tool

The effectiveness of vertical drop jumps (VDJs) to screen for non-contact ACL injuries is unclear. This may be contributed to by discrete point analysis, which does not evaluate patterns of movement. Also, limited research exists on the second landing of VDJs, potential lower limb performance asymmetries and the effect of fatigue. Statistical parametric mapping investigated the main effects of landing, limb dominance and a high intensity, intermittent exercise protocol (HIIP) on VDJ biomechanics. Twenty-two male athletes (21.9 ± 1.1 years, 180.5 ± 5.5 cm, 79.4 ± 7.8 kg) performed VDJs pre- and post-HIIP. Repeated measures ANOVA identified pattern differences during the eccentric phases of the first and second landings bilaterally. The first landing displayed greater (internal) knee flexor (η² = 0.165), external rotator (η² = 0.113) and valgus (η² = 0.126) moments and greater hip (η² = 0.062) and knee (η² = 0.080) flexion. The dominant limb generated greater knee flexor (η² = 0.062), external rotator (η² = 0.110) and valgus (η² = 0.065) moments. The HIIP only had one effect, increased thoracic flexion relative to the pelvis (η² = 0.088). Finally, the dominant limb demonstrated greater knee extensor moments during the second landing (η² = 0.100). ACL injury risk factors were present in both landings of VDJs with the dominant limb at potentially greater injury risk. Therefore, VDJ screenings should analyse both landings bilaterally.     

Time course of recovery of vertical jump height and heart rate versus running speed after a 90-km foot race

It is well known that sport and exercise play an important role in stimulating site-specific bone mineral density (BMD). However, what is less well understood is how these benefits dissipate throughout the body. Hence, the aim of the present study was to compare the BMD (recorded at nine sites throughout the skeleton) of 106 male athletes (from nine sports) with that of 15 male non-exercising age-matched controls. Given that BMD is known to increase with body mass and peak with age, multivariate and univariate analyses of covariance were performed to compare the BMD of the nine sports groups with controls (at all sites) using body mass and age as covariates. Our results confirmed a greater adjusted BMD in the arms of the upper-body athletes, the right arm of racket players and the legs of runners (compared with controls), supporting the site-specific nature (i.e. specific to the externally loaded site) of the bone remodelling response (all P?<0.01). However, evidence that bone mass acquisition is not just site-specific comes from the results of the rugby players, strength athletes, triathletes and racket players. The rugby players' adjusted BMD was the greatest of all sports groups and greater than controls at all nine sites (all P?<0.01), with differences ranging from 8% greater in the left arm to 21% in the lumbar spine. Similarly, the strength athletes' adjusted BMD was superior to that of controls at all sites (P?<0.05) except the legs. The adjusted BMD of the triathletes was significantly greater than that of the controls in both the arms and the legs as well as the thoracic and lumbar spine. The racket players not only had significantly greater right arm BMD compared with the controls but also a greater BMD of the lumbar spine, the pelvis and legs. In contrast, the low-strain, low-impact activities of keep-fit, cycling and rowing failed to benefit BMD compared with the age-matched controls. These results suggest that sporting activities involving high impact, physical contact and/or rotational forces or strains are likely to convey significant benefits not only to the loaded sites, but also to other unloaded peripheral and axial sites throughout the skeleton.     

体操游戏健身方案实施对幼儿投掷运动能力影响的运动学分析

为了评价体操游戏健身方案对幼儿投掷能力的影响,运用影像分析方法对不同年龄阶段幼儿干预前后实验组和对照组投掷过程的运动学指标进行分析,探讨体操游戏健身方案的干预效果。研究发现:干预对投掷远度的影响具有统计学差异;对幼儿的肩、肘、腕三个关节的活动范围均有影响,实验组关节活动范围较对照组增加明显,且干预对年龄越大幼儿关节活动范围影响也越大;体操游戏健身方案干预对幼儿肘关节活动范围的影响大于上肢其他两个环节,对腕关节运动幅度的影响最小,除大班孩子外其它年龄组差异均不具有统计学意义。     

Effect of 6-weeks WBVT on the behaviour of the lower limb muscle fibres during vertical jumping

The purpose of the current study was to examine the effect of 6 weeks of whole body vibration training (WBVT) on body composition, muscle activity of the gastrocnemius and vastus lateralis, gastrocnemius muscle architecture (static and dynamic) and ground reaction forces (performance jump) during the take-off phase of a countermovement jump in young healthy adult males. A total of 33 men (23.31 ± 5.62 years) were randomly assigned to a whole body vibration group (experimental group, EG_WBVT: n = 17; 22.11 ± 4.97 years) or a control group (CG: n = 16; 24.5 ± 6.27 years). The total duration of the intervention phase (WBVT) was 6 weeks with a frequency of 3 sessions per week. Statistically significant differences were observed (P ≤ 0.05) between pre- and post-test in the power peak (Δ 1.91 W · kg^?1; P = 0.001), take-off velocity (0.1 cm · s^?1; P = 0.002) and jump height (Δ 0.4 cm; P = 0.002) for EG_WBVT. There were no statistically significant differences in any of the body composition and muscle architecture variables. Moreover, no significant differences were found between EG_WBVT and CG nor changes in muscle activity during take-off phase of the gastrocnemius and vastus lateralis pre- versus post-training. This study suggests that a 6-week WBVT programme with increasing intensity improves jump performance but does not alter muscle activity nor muscle architecture in healthy young men.     

Influence of carbohydrate mouth rinsing on running and jumping performance during early morning soccer scrimmaging

Carbohydrate mouth rinse (CMR) is a novel method proposed to enhance endurance performance lasting ≤ 60 min. The current study examined the influence of CMR on anaerobic performance tasks in 11 collegiate female soccer players after an overnight fast. Athletes completed two experimental sessions, during which carbohydrate (CHO; 6% maltodextrin) or taste- and colour-matched placebo (PLA) mouth-rinse solutions were administered in a counterbalanced, double-blinded design. Three rounds of a 5-min scrimmage bout and series of performance tests including a single countermovement vertical jump (1VJ), a set of four consecutive vertical jumps, a 72-m shuttle run (SR72) and 18-m sprint comprised each trial. Thirst sensation (TS), session TS, ratings of perceived exertion (RPE) and session RPE were assessed as secondary outcomes. The first SR72 approached significance (p = 0.069), but no significant between-trials differences were observed for any of the mean performance tasks. The highest 1VJ scores did not differ for the first (CHO = 47.3 ± 3.4, PLA = 47.7 ± 3.5 cm; p = 0.43), second (CHO = 48.0 ± 4.1, PLA = 47.9 ± 3.5 cm; p = 0.82) or third bout (CHO = 47.4 ± 3.9, PLA = 48.1 ± 3.9 cm; p = 0.26). TS approached significance (p = 0.053) during the first bout. No significant differences (p > 0.05) were found for any of the perceptual variables. Current results fail to support ergogenic influence of CMR on anaerobic performance tasks in collegiate female athletes.     

Effect of ski boot rear stiffness (SBRS) on maximal ACL force during injury prone landing movements in alpine ski racing: A study with a musculoskeletal simulation model

A common anterior cruciate ligament (ACL) injury situation in alpine ski racing is landing back-weighted after a jump. Simulated back-weighted landing situations showed higher ACL-injury risk for increasing ski boot rear stiffness (SBRS) without considering muscles. It is well known that muscle forces affect ACL tensile forces during landing. The purpose of this study is to investigate the effect of different SBRS on the maximal ACL tensile forces during injury prone landings considering muscle forces by a two-dimensional musculoskeletal simulation model. Injury prone situations for ACL-injuries were generated by the musculoskeletal simulation model using measured kinematics of a non-injury situation and the method of Monte Carlo simulation. Subsequently, the SBRS was varied for injury prone landings. The maximal ACL tensile forces and contributing factors to the ACL forces were compared for the different SBRS. In the injury prone landings the maximal ACL tensile forces increased with increasing SBRS. It was found that the higher maximal ACL force was caused by higher forces acting on the tibia by the boot and by higher quadriceps muscle forces both due to the higher SBRS. Practical experience suggested that the reduction of SBRS is not accepted by ski racers due to performance reasons. Thus, preventive measures may concentrate on the reduction of the quadriceps muscle force during impact.     

Influence of recovery intensity on time spent at maximal oxygen uptake during an intermittent session in young,endurance-trained athletes

Abstract

In this study, we examined the effects of three recovery intensities on time spent at a high percentage of maximal oxygen uptake (t90[Vdot]O_2max) during a short intermittent session. Eight endurance-trained male adolescents (16 ± 1 years) performed four field tests until exhaustion: a graded test to determine maximal oxygen uptake ([Vdot]O_2max; 57.4 ± 6.1 ml · min^?1 · kg^?1) and maximal aerobic velocity (17.9 ± 0.4 km · h^?1), and three intermittent exercises consisting of repeat 30-s runs at 105% of maximal aerobic velocity alternating with 30 s active recovery at 50% (IE₅₀), 67% (IE₆₇), and 84% (IE₈₄) of maximal aerobic velocity. In absolute values, mean t90[Vdot]O_2max was not significantly different between IE₅₀ and IE₆₇, but both values were significantly longer compared with IE₈₄. When expressed in relative values (as a percentage of time to exhaustion), mean t90[Vdot]O_2max was significantly higher during IE₆₇ than during IE₅₀. Our results show that both 50% and 67% of maximal aerobic velocity of active recovery induced extensive solicitation of the cardiorespiratory system. Our results suggest that the choice of recovery intensity depends on the exercise objective.