Ina Janssen

The Effect of Assisted Jumping on Vertical Jump Height in High-Performance Volleyball Players

Assisted jumping may be useful in training higher concentric movement speed in jumping, thereby potentially increasing the jumping abilities of athletes. The purpose of this study was to evaluate the effects of assisted jump training on counter-movement vertical jump (CMVJ) and spike jump (SPJ) ability in a group of elite male volleyball players. Seven junior national team volleyball players (18.0±1.0 yrs, 200.4±6.7 cm, and 84.0±7.2 kg) participated in this within-subjects cross-over counter-balanced training study. Assisted training involved 3 sessions per week of CMVJ training with 10 kg of assistance, applied through use of a bungee system, whilst normal jump training involved equated volume of unassisted counter-movement vertical jumps. Training periods were 5 weeks duration, with a 3-week wash-out separating them. Prior to and at the conclusion of each training period jump testing for CMVJ and SPJ height was conducted. Assisted jump training resulted in gains of 2.7±0.7 cm (p<0.01, ES=0.21) and 4.6±2.6 cm (p<0.01, ES=0.32) for the CMVJ and SPJ respectively, whilst normal jump training did not result in significant gains for either CMVJ or SPJ (p=0.09 and p=0.51 respectively). The changes associated with normal jump training and assisted jump training revealed significant differences in both CMVJ and SPJ (p=<0.03) in favour of the assisted jump condition, with large effect (CMVJ, ES=1.22; SPJ, ES=1.31). Assisted jumping may promote the leg extensor musculature to undergo a more rapid rate of shortening, and chronic exposure appears to improve jumping ability.

Validity and reliability of intra-stroke kayak velocity and acceleration using a GPS-based accelerometer

The aim of this study was to assess the validity and reliability of the velocity and acceleration measured by a kayak-mounted GPS-based accelerometer units compared to the video-derived measurements and the effect of satellite configuration on velocity. Four GPS-based accelerometers units of varied accelerometer ranges (2 g or 6 g) were mounted on a kayak as the paddler performed 12 trials at three different stroke rates for each of three different testing sessions (two in the morning vs. one in the afternoon). The velocity and acceleration derived by the accelerometers was compared with the velocity and acceleration derived from high-speed video footage (100 Hz). Validity was measured using Bland and Altman plots, R 2, and the root of the mean of the squared difference (RMSe), while reliability was calculated using the coefficient of variation, R 2, and repeated measures analysis of variance (ANOVA) tests. The GPS-based accelerometers under-reported kayak velocity by 0.14–0.19 m/s and acceleration by 1.67 m/s2 when compared to the video-derived measurements. The afternoon session reported the least difference, indicating a time of day effect on the velocity measured. This study highlights the need for sports utilising GPS-based accelerometers, such as minimaxX, for intra-stroke measurements to conduct sport-specific validity and reliability studies to ensure the accuracy of their data.

Predicting the patellar tendon force generated when landing from a jump

PURPOSE Although high patellar tendon loading is believed to be the primary causative factor for patellar tendinopathy, research investigating factors that affect patellar tendon loading during landing is scarce. Therefore, the purpose of this study was to identify whether factors previously associated with the development of patellar tendinopathy, and selected variables characterizing landing technique, could predict patellar tendon loading incurred by volleyball players when landing from a jump. METHODS Ten highly skilled male, 20 skilled male, and 20 skilled female volleyball players performed a lateral stop-jump movement. Sex, skill level, quadriceps strength, quadriceps extensibility, and trunk moment of inertia were recorded. Landing kinematics (250 Hz) and kinetics (1500 Hz) were collected, and peak patellar tendon force and patellar tendon force loading rate were calculated. Backward multiple regression analyses identified which risk factors or landing technique variables were predictors of patellar tendon loading. RESULTS Multiple regression analyses were able to estimate and predict 52% (F4,49 = 14.258, P < 0.001) and 70% (F4,49 = 29.329, P < 0.001) of the peak patellar tendon force and the patellar tendon force loading rate variance, respectively. The present study revealed that male volleyball players with greater quadriceps strength, who displayed increased ankle dorsiflexion velocity and trunk flexion velocity during landing, were predicted to incur higher patellar tendon loading. CONCLUSIONS As frequent application of high patellar tendon loading has previously been identified as a causative factor for developing patellar tendinopathy, interventions designed to decrease ankle dorsiflexion velocity and trunk flexion velocity at landing, particularly in male players with strong quadriceps muscles, may be effective in reducing patellar tendon loading and, in turn, patellar tendinopathy prevalence in this population.

Lower Extremity Kinematics and Kinetics When Landing From Unloaded and Loaded Jumps

Countermovement jumps loaded with a weighted vest are often used for the training of lower body power to improve jump performance. However, it is currently unknown how this added load affects the lower extremity kinematics and kinetics, in particular whether this results in an increased injury risk. Therefore, the purpose of this investigation was to determine how lower extremity kinematics and kinetics during landing are affected by loaded jumps as demonstrated in a volleyball block jump landing. Ten elite male volleyball players performed block jump landings in an unloaded and loaded (9.89 kg) condition. Kinematic and kinetic landing data from the three highest jumps were collected and assessed. Paired samples t test was used to establish whether load condition had a significant effect on lower extremity kinematics and kinetics. Hip flexion was significantly greater in the unloaded condition compared with the loaded condition (p = .004). There was no significant difference in any other kinematic or kinetic variables measures between the unloaded and loaded conditions. These results suggest that landing from loaded volleyball block jumps does not increase injury risk compared with unloaded jumps in elite male volleyball players.

Variations in jump height explain the between-sex difference in patellar tendon loading during landing

Patellar tendinopathy is the most common overuse knee injury in volleyball, with men reporting more than twice the injury prevalence than women. Although high patellar tendon loading is thought to be a causative factor of patellar tendinopathy, it is unknown whether between‐sex variations in landing technique account for differences in patellar tendon loading. It was hypothesized that male volleyball players would display differences in landing technique and would generate higher patellar tendon loading than their female counterparts. The landing technique and patellar tendon loading of 20 male and 20 female volleyball players performing a lateral stop‐jump block movement were collected. Independent t‐tests were used to identify any between‐sex differences in landing technique with the data grouped to account for differences in jump height and in anthropometry. Male volleyball players were taller and heavier, landed from a higher height, displayed differences in landing kinematics, generated a significantly greater knee extensor moment, and experienced higher patellar tendon loading than female players when all 40 participants were compared. However, when participants were matched on jump height, they generated similar patellar tendon loading, irrespective of their sex. These results imply that jump height is a more important determinant of patellar tendon loading than sex.

Sex differences in neuromuscular recruitment are not related to patellar tendon load

PURPOSE Although male volleyball players report a greater prevalence of patellar tendinopathy than female players, it remains unknown whether higher patellar tendon loading generated during landing by male players is related to sex-specific neuromuscular recruitment patterns. This study aimed to investigate the relationship between neuromuscular recruitment patterns and patellar tendon loading during landing and to determine whether there were any significant differences in lower limb neuromuscular recruitment patterns displayed by male and female volleyball players during landing. METHODS The neuromuscular recruitment patterns and patellar tendon loading of 20 male and 20 female volleyball players performing a lateral stop-jump block movement were recorded and calculated. Pearson product-moment correlations were conducted to determine whether neuromuscular recruitment patterns were related to the peak patellar tendon force or patellar tendon force loading rate generated at landing. Independent t-tests were applied to a subset of data for 13 males and 13 females matched for jump height to identify any between-sex differences in neuromuscular recruitment patterns. RESULTS Later onset of rectus femoris (r = 0.312), vastus medialis (r = 0.455), and biceps femoris (r = 0.330) were significantly correlated with a higher patellar tendon force loading rate, although these correlation values were weak. Male volleyball players displayed significantly earlier biceps femoris and semitendinosus onset, and significantly earlier peak semitendinosus activity compared with their female counterparts. CONCLUSION Although male and female volleyball players displayed significantly different muscle onset times, these patterns were not strongly related to patellar tendon loading at landing. It is likely that a multitude of factors, including the frequency of patellar tendon loading, more strongly contributes to developing patellar tendinopathy than neuromuscular recruitment patterns in isolation.

The relationship between patellar tendinopathy risk factors and ground reaction forces during cross-over block jump landings

Background Overuse knee injuries, such as patellar tendinopathy, are one of the most prevalent and frequent injuries in volleyball with up to 50% of male indoor volleyball players sustaining this injury in their careers. Objective The aim of this research was to examine the intrinsic and extrinsic risk factors associated with patellar tendinopathy including muscle flexibility, muscle strength, vertical jump, and their relationship to vertical ground reaction forces (vGRF) during cross-over block jump landings. Design Structural alignment, lower limb flexibility, and muscle strength assessed were measured for each participant who then performed five trials of a cross-over step block. vGRF (vGRF: 1500 Hz; Kistler) were collected for takeoff and landing. Setting A portable volleyball net was used to simulate a typical and realistic volleyball condition in a biomechanics laboratory. A standard volleyball was mounted on a post and used as a target. Participants Elite male (EM) (N=10), sub-elite male (SEM) (N=10), and sub-elite female (N=10) volleyball players with no existing knee joint injury or history of lower limb surgery participated in this study. Main outcome measurements Magnitudes of and correlations among risk factor measures and peak vGRF. Results Gender differences were observed with SEM displaying significantly smaller Q-angle (p=0.04), greater strength (p=0.00), and maximal jump height (p=0.00) than SEF. EM displayed passive greater hip extension (p=0.01) and trunk flexion (p=0.05), and significantly greater strength in their non-dominant quadriceps (p=0.01) than SEM. SEM generated significantly higher vGRF compared to SEF. Significant negative correlations were found between vGRF and Q-angle and gastrocnemius flexibility for SEF but not SEM or EM. Conclusions The results of this study may provide further insight why and which volleyball athletes may be prone to developing overuse knee injuries.

Previously identified patellar tendinopathy risk factors differ between elite and sub-elite volleyball players

Patellar tendinopathy is the most common knee injury incurred in volleyball, with its prevalence in elite athletes more than three times that of their sub‐elite counterparts. The purpose of this study was to determine whether patellar tendinopathy risk factors differed between elite and sub‐elite male volleyball players. Nine elite and nine sub‐elite male volleyball players performed a lateral stop–jump block movement. Maximum vertical jump, training history, muscle extensibility and strength, three‐dimensional landing kinematics (250 Hz), along with lower limb neuromuscular activation patterns (1500 Hz), and patellar tendon loading were collected during each trial. Multivariate analyses of variance (P < 0.05) assessed for between‐group differences in risk factors or patellar tendon loading. Significant interaction effects were further evaluated using post‐hoc univariate analysis of variance tests. Landing kinematics, neuromuscular activation patterns, patellar tendon loading, and most of the previously identified risk factors did not differ between the elite and sub‐elite players. However, elite players participated in a higher training volume and had less quadriceps extensibility than sub‐elite players. Therefore, high training volume is likely the primary contributor to the injury discrepancy between elite and sub‐elite volleyball players. Interventions designed to reduce landing frequency and improve quadriceps extensibility are recommended to reduce patellar tendinopathy prevalence in volleyball players.

The effect of leg dominance and landing height on ACL loading among female athletes

Female athletes are more prone to anterior cruciate ligament (ACL) injury. A neuromuscular imbalance called leg dominance may provide a biomechanical explanation. Therefore, the purpose of this study was to compare the side-to-side lower limb differences in movement patterns, muscle forces and ACL forces during a single-leg drop-landing task from two different heights. We hypothesized that there will be significant differences in lower limb movement patterns (kinematics), muscle forces and ACL loading between the dominant and non-dominant limbs. Further, we hypothesized that significant differences between limbs will be present when participants land from a greater drop-landing height. Eight recreational female participants performed dominant and non-dominant single-leg drop landings from 30 to 60cm. OpenSim software was used to develop participant-specific musculoskeletal models and to calculate muscle forces. We also predicted ACL loading using our previously established method. There were no significant differences between dominant and non-dominant leg landing except in ankle dorsiflexion and GMED muscle forces at peak GRF. Landing from a greater height resulted in significant differences among most kinetics and kinematics variables and ACL forces. Minimal differences in lower-limb muscle forces and ACL loading between the dominant and non-dominant legs during single-leg landing may suggest similar risk of injury across limbs in this cohort. Further research is required to confirm whether limb dominance may play an important role in the higher incidence of ACL injury in female athletes with larger and sport-specific cohorts.

JUMP HEIGHT IS THE CRITICAL FACTOR AFFECTING BETWEEN-SEX DIFFERENCES IN PATELLAR TENDON LOADING DURING LANDING IN VOLLEYBALL

Background Patellar tendinopathy is the most common overuse knee injury in volleyball, with men reporting more than twice the injury prevalence than women. However, whether between-sex variations in landing technique account for differences in patellar tendon loading is unknown. Objective Our objective was to compare the landing technique and patellar tendon loading in male and female volleyball players. We hypothesised that males would display differences in landing technique and generate higher patellar tendon loading due to having a higher jump height than the females. Design Controlled laboratory study. Setting A regulation height volleyball net and mounted volleyball were used to simulate volleyball court conditions. Participants Forty male and female volleyball players volunteered for this study. Participants were excluded if they were injured at the time of testing, had a history of lower limb surgery, equilibrium disorders, or orthopaedic or neurologic conditions that could influence their landing biomechanics. Risk factor assessment Independent t-tests were used to identify whether there were any between-sex differences in all 20 males and 20 females, or 13 males and 13 females matched for jump height. Main outcome measurements Three-dimensional lower limb kinematics were calculated to characterise landing technique. Patellar tendon loading was characterised by peak patellar tendon force and patellar tendon force loading rate. Results Males landed from a higher height (P<.001), displayed differences in landing kinematics (P<.05), and experienced higher patellar tendon loading (P=.002), than female players. These differences, however, dissipated when the participants were matched for jump height. Conclusions Jump height is the critical factor affecting patellar tendon loading, whereby a higher jump height is associated with higher patellar tendon loading, irrespective of sex. The between-sex disparity in patellar tendinopathy may, therefore, be due to males landing from greater heights causing higher patellar tendon loading, rather than being sex-related differences in landing technique.