Unilateral Drop Jumps Research Articles

Jumping towards field-based ground reaction force estimation and assessment with OpenCap

Low-cost and field-viable methods that can simultaneously assess external kinetics and kinematics are necessary to enhance field-based biomechanical monitoring. The aim of this study was to determine the accuracy and usability of ground reaction force (GRF) profiles estimated from segmental kinematics, measured with OpenCap (a low-cost markerless motion-capture system), during common jumping movements. Full-body segmental kinematics were recorded for fifteen recreational athletes performing countermovement, squat, bilateral drop, and unilateral drop jumps, and used to estimate vertical GRFs with a mechanics-based method. Eleven distinct performance-, fatigue-, or injury-related GRF variables were then validated against a gold-standard force platform. Across jumping movements, a total of six and three GRF variables were estimated with a bias or limits of agreement <5 % respectively. Bias and limits of agreement were between 5 and 15 % for seventeen and nineteen variables respectively. Moreover, we show that estimated force variables with a bias <15 % can adequately assess the within-athlete changes in GRF variables between jumping conditions (arm swing or leg dominance). These findings indicate that using a low-cost and field-viable markerless motion capture system (OpenCap) to estimate and assess GRF profiles during common jumping movements is approaching acceptable limits of accuracy. The presented method can be used to monitor force variables of interest and examine underlying segmental kinematics. This application is a jump towards researchers and sports practitioners performing biomechanical monitoring of jumping efficiently, regularly, and extensively in field settings.

Effect of individualised strength and plyometric training on the physical performance of basketball players

ABSTRACT The aims of this study were to examine the effects of eight weeks of individualised force-velocity imbalance (F-Vimb) training on physical performance in basketball players and to analyse the differences in physical performance between two periods of time (four to eight weeks) with this training. Thirty male players (age, 22.8 ± 5.68 years; height, 1.87 ± 0.07 m; body mass, 86.3 ± 11.1 kg) were divided into an intervention group (INT, n = 15), who performed an individualised training based on individual F-Vimb; and a control group (CON, n = 15), who underwent a non-individualised training programme; both groups performed two days/week of intervention and the same pre-season basketball training. At baseline, at four weeks, and at eight weeks of intervention, an assessment was performed including countermovement-jumps, unilateral drop jumps, triple hop test, force-velocity profile, sprint and change of direction (COD). At four weeks, the INT showed improvements in sprint and vertical jumping actions (≥3.76%, ES ≥0.44, p ≤ 0.02). At eight weeks, the INT continued to improve vertical jumping actions (p < 0.05) and showed improvements in horizontal jumping (6.80%, ES = 0.45, p < 0.01) and COD (≥2.99%, ES ≥0.96, p < 0.01). A significant reduction in F-Vimb was observed for INT (ES = 0.77, p = 0.01). In contrast, none of these changes were observed in CON. Thus, an individualised F-Vimb training intervention improved physical performance after eight weeks, with changes in sprint and vertical jump after first four weeks. Basketball coaches should optimise the force-velocity profile and improve the performance in sport-related actions as jumping and changing direction.

Assessments performed on harder surfaces can misrepresent ACL injury risk

ABSTRACT Changes in surface hardness are likely to alter an athlete’s movement strategy. Anterior cruciate ligament (ACL) injury risk assessments that are performed on a different surface to that used for training and competition may, therefore, not represent an athlete’s on-field movement strategies. The aim of this study was to examine the influence of surface hardness on multidirectional field sport athletes’ movement strategies in movements that are commonly used in ACL injury risk assessments (bilateral and unilateral drop jumps, and a cutting manoeuvre). Ground reaction forcesand three-dimensional lower limb kinematics were recorded from 19 healthy, male, multidirectional field sport athletes performing bilateral and unilateral drop jumps, and a 90° cutting task on Mondo track (harder surface) and artificial turf (softer surface). Continuous (statistical parametric mapping) and discrete analyses revealed alterations in vertical and horizontal braking forces and knee and hip moments between surfaces of different hardness in all three movements (p ≤ 0.05, d > 0.5). Injury risk assessments performed on a harder surface (e.g. Mondo track) can misrepresent an athlete’s risk of ACL injury compared to the same movements performed on a softer more cushioned surface that is typically used for training and/or matches (e.g. artificial turf).

Angular Velocities and Linear Accelerations Derived from Inertial Measurement Units Can Be Used as Proxy Measures of Knee Variables Associated with ACL Injury

Given the high rates of both primary and secondary anterior cruciate ligament (ACL) injuries in multidirectional field sports, there is a need to develop easily accessible methods for practitioners to monitor ACL injury risk. Field-based methods to assess knee variables associated with ACL injury are of particular interest to practitioners for monitoring injury risk in applied sports settings. Knee variables or proxy measures derived from wearable inertial measurement units (IMUs) may thus provide a powerful tool for efficient injury risk management. Therefore, the aim of this study was to identify whether there were correlations between laboratory-derived knee variables (knee range of motion (RoM), change in knee moment, and knee stiffness) and metrics derived from IMUs (angular velocities and accelerations) placed on the tibia and thigh, across a range of movements performed in practitioner assessments used to monitor ACL injury risk. Ground reaction forces, three-dimensional kinematics, and triaxial IMU data were recorded from nineteen healthy male participants performing bilateral and unilateral drop jumps, and a 90° cutting task. Spearman's correlations were used to examine the correlations between knee variables and IMU-derived metrics. A significant strong positive correlation was observed between knee RoM and the area under the tibia angular velocity curve in all movements. Significant strong correlations were also observed in the unilateral drop jump between knee RoM, change in knee moment, and knee stiffness, and the area under the tibia acceleration curve (rs = 0.776, rs = -0.712, and rs = -0.765, respectively). A significant moderate correlation was observed between both knee RoM and knee stiffness, and the area under the thigh angular velocity curve (rs = 0.682 and rs = -0.641, respectively). The findings from this study suggest that it may be feasible to use IMU-derived angular velocities and acceleration measurements as proxy measures of knee variables in movements included in practitioner assessments used to monitor ACL injury risk.

Acute effects of combined isometric and plyometric conditioning activities on sports performance and tendon stiffness in female volleyball players.

This study aimed to compare the effects of bilateral and unilateral conditioning activities (CA; combined isometric and plyometric) on countermovement jump performance, modified t-agility test, Achilles tendon stiffness and skin surface temperature. Thirteen female semi-professional volleyball players performed two CAs in random order: 1) bilateral isometric half back squats followed by bilateral drop jumps (BI-CA); and 2) unilateral isometric half back squats followed by unilateral drop jumps (UNI-CA). To assess the effects of CAs, countermovement jump, modified t-agility test, Achilles tendon stiffness and skin surface temperature measurements were performed 5 min before and 6 min after the CA. Both CAs significantly increased thigh skin surface temperature from pre- to post-CA (BI-CA, p < 0.001; effect size [ES] = 1.41 and UNI-CA, p = 0.001; ES = 1.39) but none of them influenced modified t-agility test time (interaction: p = 0.338, main effect of time: p = 0.121 and condition: p = 0.819). The countermovement jump height and modified reactive strength index significantly increased from pre-to post-CA during the BI-CA condition (p = 0.003, ES = 0.45, and p = 0.008, ES = 0.48) but not for UNI-CA (p = 0.061, ES = 0.18 and p = 0.065, ES = 0.26). No significant impact has been found for countermovement depth (interaction: p = 0.054, main effect of time: 0.097, and condition: p = 0.41) as well as for contraction time (interaction: p = 0.536, main effect of time: p = 0.224, and condition: p = 0.807). Moreover, stronger and weaker limb CMJ relative peak force significantly decreased from pre-to post-CA (p = 0.014, ES = −0.31, and p = 0.027, ES = −0.26; respectively) during UNI-CA condition but not for BI-CA (p = 0.096, ES = 0.23, and p = 1.41, ES = 0.18). The stronger and weaker limb Achilles tendon stiffness significantly increased from pre-to post-CA during the UNI-CA condition (p = 0.013, ES = 0.60 and p < 0.001, ES = 0.79; respectively) but not for BI-CA (p = 0.66; ES = 0.15 and p = 0.265; ES = 0.42). Furthermore, the post-CA stronger limb Achilles tendon stiffness during the UNI-CA was significantly higher than that noted during the BI-CA (p = 0.006, ES = 0.7). The present study showed that combined isometric and plyometric bilateral CA effectively improved the countermovement jump but did not enhance the t-agility test performance. These findings indicate that exercise combinations could effectively produce a post-activation performance enhancement effect but should replicate the following explosive task as much as possible.

The effect of a core training program on jump performance in female handball players

Objectives: To evaluate changes on bilateral and unilateral jump performance and frontal knee projection angle after an implementation of a core strength program in female handball players.&#x0D; Equipment and methods: This is a randomized controlled trial study. A total of 20 participants [age = 17.2 (1.9) years, height = 1.7 (0.1) m, weight = 62.8 (7) kg ] were recruited and split in: a core training group and a control group. The core training group participated in 8 weeks in-season of a core strength program (2 times/week). Pre- and post-intervention jump height, contact time and reactive strength index were collected during bilateral and unilateral drop vertical jumps. Frontal knee projection angle was measured only at unilateral drop jumps.&#x0D; Results: Core training group increased the bilateral jump height by 18.8% and showed a statistically significant difference in reactive strength index from pre-intervention [0.07 (0.03)] to post-intervention [0.10 (0.04)]. The core training group also improved the unilateral jump height by 20%, but only at the non-dominant leg. This improvement was accompanied by a statistically significant decreased in the frontal knee projection angle from pre-intervention [13.8 (7.38) degrees] to post-intervention [9.3 (6.09) degrees]. Statistical significant difference was set at p ˂0.05.&#x0D; Conclusion: A core strength training increased jump performance and it could play a role in ACL injury prevention programs in female team players.&#x0D; &#x0D;

Seasonal Variation of Physical Performance and Inter-limb Asymmetry in Professional Cricket Athletes.

Bishop, C, Weldon, A, Hughes, J, Brazier, J, Loturco, I, Turner, A, and Read, P. Seasonal variation of physical performance and interlimb asymmetry in professional cricket athletes. J Strength Cond Res 35(4): 941-948, 2021-The aims of this study were to: (a) determine the seasonal variation of physical performance in professional cricket players and (b) determine the seasonal variation of interlimb asymmetries in the same cohort of professional players. Fifteen male professional cricket players (age: 20.60 ± 1.59 years; height: 1.82 ± 0.08 m; and body mass: 78.70 ± 11.23 kg) performed unilateral countermovement jumps (CMJs), unilateral drop jumps, 10 m sprints and 505 change of direction (COD) speed tests at pre (March), mid (June), and end (September) of the 2018 season. Interlimb asymmetry was quantified in the unilateral CMJ (jump height and concentric impulse), unilateral drop jump (jump height and reactive strength index [RSI]), and 505 (total time and COD deficit). Significant changes (p < 0.05) were evident for the following tests: unilateral CMJ (effect size [ES] range = 0.67-1.00), 505 on the right leg (ES = 0.70), 10 m (ES range = -1.39 to 0.70), and COD deficit (ES range = 0.70-0.80), with the largest changes evident for 10-m sprint. No significant differences were evident in drop jump performance throughout the season. For the magnitude of asymmetry, significant changes in jump height asymmetry from the unilateral CMJ were evident from mid to end of season (ES = 0.72). For the direction of asymmetry, levels of agreement ranged from poor to substantial in the unilateral CMJ (kappa = -0.21 to 0.72), fair to substantial in the unilateral drop jump (kappa range = 0.33 to 0.74), and slight to moderate during the 505 test (kappa range = 0.06 to 0.44), with RSI showing noticeably better results than other tests or metrics. These data show that the largest changes in performance scores throughout the season came from the 10-m test, which practitioners may wish to consider implementing if not doing so already. Furthermore, both unilateral jump tests showed their use for asymmetry interpretation, which practitioners may wish to consider implementing in to their test batteries. Specifically, jump height asymmetry during the unilateral CMJ was the only metric to exhibit meaningful changes between time points, whereas RSI was the metric that exhibited more consistent limb dominance characteristics for the direction of asymmetry.

Effects of pelvic and core strength training on biomechanical risk factors for anterior cruciate ligament injuries.

Little is known about the changes in biomechanical risk factors for an anterior cruciate ligament (ACL) injury after participation in a pelvic and core strength training (PCST) program in female team players. This is a randomized controlled trial for which a total of 29 female soccer players were recruited from a soccer club and split into two groups, namely, experimental group (EG, N.=18; mean [SD] age, 17.8 [2.0 years], weight 64.0 [6.6] kg and height 1.7 [0.0] m) and control group (control, N.=11; mean [SD] age, 16.2 [1.2] years, weight 61.6 [7.3] kg and height 1.7 [0.0] m). The EG participated in an in-season 8-week PCST program (twice/week). Participants in the CG performed their normal training without additional pelvic and core strengthening. Pre- and postintervention knee frontal plane projection angle (FPPA), hip, knee and ankle peak flexion angles and jump height were collected during bilateral and unilateral drop jumps. PCST significantly reduced FPPA at dynamic landing, in both dominant (-7.1º) and non-dominant lower extremities (-8º). Further, this training significantly increased the peak hip (24.4º) and knee flexion angles (14.94º), but not the peak ankle dorsiflexion angle (P>0.05) which, significantly decreased in the CG (-3.5º). Following the intervention, EG significantly increased measures obtained for both bilateral (2.84 cm) and unilateral jumps (1.33 cm for the dominant leg and 1.22 cm for the non-dominant leg) (P<0.05), not so for CG (P<0.05). PCST resulted in improvements on ACL injury risk factors and vertical drop jump performance, suggesting that strengthening this body part warrants not only injury prevention, but increases jumping performance.

Magnitude or Direction? Seasonal Variation of Interlimb Asymmetry in Elite Academy Soccer Players.

Bishop, C, Read, P, Chavda, S, Jarvis, P, Brazier, J, Bromley, T, and Turner, A. Magnitude or direction? Seasonal variation of interlimb asymmetry in elite academy soccer players. J Strength Cond Res 36(4): 1031-1037, 2022-Previous research has highlighted a distinct lack of longitudinal data for asymmetry. The aims of this study were to provide seasonal variation data for the magnitude and direction of asymmetry. Eighteen elite male academy soccer players (under-23) performed unilateral countermovement jumps (CMJs) and unilateral drop jumps (DJs) during pre-season, mid-season, and end of season time points. Recorded metrics for asymmetry included jump height and concentric impulse for the CMJ, and jump height and reactive strength index for the DJ. The magnitude of asymmetry showed trivial to small changes throughout the season (CMJ effect size [ES] range = -0.43 to 0.05; DJ ES range = -0.18 to 0.41). However, Kappa coefficients showed poor to substantial levels of agreement for the direction of asymmetry during the CMJ (Kappa = -0.06 to 0.77) and DJ (Kappa = -0.10 to 0.78) throughout the season. These data show that when monitoring asymmetry, the magnitude alone may provide a false impression of consistent scores over time. By contrast, monitoring the direction of asymmetry highlights its task and variable nature and is suggested as a useful tool for practitioners who wish to monitor asymmetry over the course of a competitive soccer season.

The Association Between Interlimb Asymmetry and Athletic Performance Tasks: A Season-Long Study in Elite Academy Soccer Players.

Bishop, C, Read, P, Bromley, T, Brazier, J, Jarvis, P, Chavda, S, and Turner, A. The association between interlimb asymmetry and athletic performance tasks: A season-long study in elite academy soccer players. J Strength Cond Res 36(3): 787-795, 2022-The aims of this study were to determine the association between asymmetry and measures of speed and change of direction speed (CODS) performance throughout a competitive soccer season and, determine whether any observed changes in asymmetry were associated with changes in speed and CODS performance. Eighteen elite male under-23 academy soccer players performed unilateral countermovement jumps, unilateral drop jumps (DJ), 10- and 30-m sprints, and 505 CODS tests at pre, mid, and end of season. No significant relationships were evident during preseason or midseason between asymmetry and speed or CODS performance. Significant correlations were shown at the end of season between DJ height asymmetry and 10-m sprint time (ρ = 0.62; p = 0.006) and 505 time on the right limb (ρ = 0.65; p = 0.003). No significant correlations between changes in asymmetry and changes in speed or CODS were evident at any time point. Although numerous studies have reported associations between asymmetry and reduced athletic performance, it seems that these associations with speed and CODS do not track consistently over time. Thus, suggestions for the reduction of asymmetry that may indirectly enhance athletic performance cannot be made.

Predictors of Linear and Multidirectional Acceleration in Elite Soccer Players.

Jonathan, N, Russell, M, Shearer, D, Cook, CJ, and Kilduff, LP. Predictors of linear and multidirectional acceleration in elite soccer players. J Strength Cond Res 33(2): 514-522, 2019-Linear and multidirectional acceleration underpins success in professional soccer match play. However, the physical qualities that determine these performance indicators are poorly understood in elite players. English Premier League players (n = 26) performed isometric midthigh pulls (IMTPs), bilateral and unilateral drop jumps (from 40 and 20 cm, respectively), bilateral and unilateral countermovement jumps (CMJs), and assessments of linear (5, 10, and 20 m) and multidirectional (left and right preplanned and reactive) acceleration. Regression analyses highlighted that 21% of variance in 5-m sprint time (1.02 ± 0.07 seconds) was explained by relative peak power output (PPO) in bilateral CMJ (54.5 ± 5.3 W·kg). A 5.4 W·kg increase in CMJ predicted a 0.03-second decrease in 5-m sprint time (P = 0.02). For 10-m sprint time (1.72 ± 0.09 seconds), 44% of variance was explained by isometric relative peak force ([PF]; 30.4 ± 4.9 N·kg) and bilateral relative CMJ PPO (54.5 ± 5.3 W·kg). A 5.4 W·kg increase in CMJ predicted reduced 10-m sprint times by 0.04 seconds (P = 0.01). For 20-m sprint time (2.94 ± 0.11 seconds), 55% of the total variance was explained by isometric relative PF (30.4 ± 4.9 N·kg) and relative CMJ PPO (54.5 ± 5.3 W·kg). Increases of 5.4 W·kg in bilateral CMJ predicted an improvement of 20-m sprint time by 0.06 seconds (P = 0.002). Contributions were insignificant (P > 0.05) for preplanned and reactive multidirectional acceleration. Relativized indices, especially those related to force production during CMJ and IMTP tests, likely underpin linear but not multidirectional acceleration performance in professional soccer players. When linear acceleration is a training focus, practitioners should seek to monitor CMJ and IMTP test performance.

Vertical stiffness asymmetries during drop jumping are related to ankle stiffness asymmetries.

Asymmetry in vertical stiffness has been associated with increased injury incidence and impaired performance. The determinants of vertical stiffness asymmetry have not been previously investigated. Eighteen healthy men performed three unilateral drop jumps during which vertical stiffness and joint stiffness of the ankle and knee were calculated. Reactive strength index was also determined during the jumps using the ratio of flight time to ground contact time. "Moderate" differences in vertical stiffness (t17 =5.49; P<0.001), "small" differences in center of mass displacement (t17 =-2.19; P=0.043), and "trivial" differences in ankle stiffness (t17 =2.68; P=0.016) were observed between stiff and compliant limbs. A model including ankle stiffness and reactive strength index symmetry angles explained 79% of the variance in vertical stiffness asymmetry (R2 =0.79; P<0.001). None of the symmetry angles were correlated to jump height or reactive strength index. Results suggest that asymmetries in ankle stiffness may play an important role in modulating vertical stiffness asymmetry in recreationally trained men.

Relationship of the functional movement screen in-line lunge to power, speed, and balance measures.

Background:The in-line lunge of the Functional Movement Screen (FMS) evaluates lateral stability, balance, and movement asymmetries. Athletes who score poorly on the in-line lunge should avoid activities requiring power or speed until scores are improved, yet relationships between the in-line lunge scores and other measures of balance, power, and speed are unknown.Hypothesis:(1) Lunge scores will correlate with center of pressure (COP), maximum jump height (MJH), and 36.6-meter sprint time and (2) there will be no differences between limbs on lunge scores, MJH, or COP.Study Design:Descriptive laboratory study.Level of Evidence:Level 3.Methods:Thirty-seven healthy, active participants completed the first 3 tasks of the FMS (eg, deep squat, hurdle step, in-line lunge), unilateral drop jumps, and 36.6-meter sprints. A 3-dimensional motion analysis system captured MJH. Force platforms measured COP excursion. A laser timing system measured 36.6-m sprint time. Statistical analyses were used to determine whether a relationship existed between lunge scores and COP, MJH, and 36.6-m speed (Spearman rho tests) and whether differences existed between limbs in lunge scores (Wilcoxon signed-rank test), MJH, and COP (paired t tests).Results:Lunge scores were not significantly correlated with COP, MJH, or 36.6-m sprint time. Lunge scores, COP excursion, and MJH were not statistically different between limbs.Conclusion:Performance on the FMS in-line lunge was not related to balance, power, or speed. Healthy participants were symmetrical in lunging measures and MJH.Clinical Relevance:Scores on the FMS in-line lunge should not be attributed to power, speed, or balance performance without further examination. However, assessing limb symmetry appears to be clinically relevant.

The Effect of Short-Term Resistance Training on Hip and Knee Kinematics During Vertical Drop Jumps

The purpose of this study was to determine the effect of a weight-bearing free weight resistance training program alone on knee flexion, hip flexion, and knee valgus during unilateral and bilateral drop jump tasks. Twenty-nine young adult females with previous athletic experience were randomly divided into a control (n = 16) and a resistance training (n = 13) groups. The resistance training group completed 8 weeks of lower extremity, weight-bearing exercises using free weights, whereas the control group did not train. A pre- and posttest was conducted to measure knee valgus, knee flexion, and hip flexion during unilateral (30 cm) and bilateral (60 cm) vertical drop jumps for maximum height. Joint angles were determined using 3-dimensional electromagnetic tracking sensors (MotionMonitor; Innovative Sports Training, Inc., Chicago, IL, USA). Initial training intensity for the bilateral squat was 50% of the subject's 1 repetition maximum (RM), which increased 5% each week to 85% during the final week. Sets and repetitions ranged from 2 to 4 and from 4 to 12, respectively. The training loads for all other exercises (lunge, step-up, unilateral squat, and Romanian deadlift) increased from 15RM to 6RM from the initial to the final week. A repeated measures analysis of variance was used to determine differences in the hip and knee joint angles. No significant differences for knee valgus and hip flexion measures were found between the groups after training; however, knee flexion angle significantly increased in the training group from the pretest (77.2 ± 4.1°) to posttest (83.2 ± 3.7°) during the bilateral drop jump. No significant changes occurred during the unilateral drop jump. Bilateral measures for knee flexion, hip flexion, and knee valgus were significantly (p < 0.05) greater than the unilateral measures during the drop jump task, which indicate an increased risk for anterior cruciate ligament (ACL) injury during unilateral drop jumps. The data support that the strength and conditioning specialist can implement resistance training alone during a short-term training period to reduce the risk of ACL injury by increasing knee flexion during a bilateral drop jump task. Increased knee flexion angles after resistance training may indicate a reduced risk for knee injury from improved neuromuscular control, resulting in a softer landing.

The Effects of Floor Incline on Lower Extremity Biomechanics During Unilateral Landing From a Jump in Dancers

Retrospective studies have suggested that dancers performing on inclined ("raked") stages have increased injury risk. One study suggests that biomechanical differences exist between flat and inclined surfaces during bilateral landings; however, no studies have examined whether such differences exist during unilateral landings. In addition, little is known regarding potential gender differences in landing mechanics of dancers. Professional dancers (N = 41; 14 male, 27 female) performed unilateral drop jumps from a 30 cm platform onto flat and inclined surfaces while extremity joint angles and moments were identified and analyzed. There were significant joint angle and moment effects due to the inclined flooring. Women had significantly decreased peak ankle dorsiflexion and hip adduction moment compared with men. Findings of the current study suggest that unilateral landings on inclined stages create measurable changes in lower extremity biomechanical variables. These findings provide a preliminary biomechanical rationale for differences in injury rates found in observational studies of raked stages.