Determinants of countermovement jump performance: a kinetic and kinematic analysis

The Association of Age, Sex, and BMI on Lower Limb Neuromuscular and Muscle Mechanical Function in People with Multiple Sclerosis

(1) Background: The countermovement jump (CMJ) on a force plate could be a sensitive assessment for detecting early lower-limb muscle mechanical deficits in the early stages of multiple sclerosis (MS). CMJ performance is known to be influenced by various anthropometric, physiological, and biomechanical factors, mostly investigated in children and adult athletes. Our aim was to investigate the association of age, sex, and BMI with muscle mechanical function using CMJ to provide a comprehensive overview of lower-limb motor function in people with multiple sclerosis (pwMS). (2) Methods: A cross-sectional study was conducted with pwMS (N = 164) and healthy controls (N = 98). All participants performed three maximal CMJs on a force plate. Age, sex, and BMI were collected from all participants. (3) Results: Significant age, sex, and BMI effects were found for all performance parameters, flight time, and negative and positive power for pwMS and HC, but no significant interaction effects with the group (pwMS, HC) were detected. The highest significant effects were found for sex on flight time (η2 = 0.23), jump height (η2 = 0.23), and positive power (η2 = 0.13). PwMS showed significantly lower CMJ performance compared to HC in middle-aged (31-49 years), with normal weight to overweight and in both women and men. (4) Conclusions: This study showed that age, sex, and BMI are associated with muscle mechanical function in pwMS and HC. These results may be useful in developing reference values for CMJ. This is a crucial step in integrating CMJ into the diagnostic assessment of people with early MS and developing individualized and effective neurorehabilitative therapy.

Sensitive Identification of Asymmetries and Neuromuscular Deficits in Lower Limb Function in Early Multiple Sclerosis

BACKGROUND

In the early stages of multiple sclerosis (MS), there are no objective sensitive functional assessments to identify and quantify early subclinical neuromuscular deficits and lower limb strength asymmetries during complex movements. Single-countermovement jumps (SLCMJ), a maximum single leg vertical jump, on a force plate allow functional evaluation of unilateral lower limb performance in performance diagnostics and could therefore provide early results on asymmetries in MS.

OBJECTIVE

Objective evaluation of early lower limb neuromuscular deficits and asymmetries in people with multiple sclerosis (pwMS) using SLCMJ on a force plate.

METHODS

A study was conducted with pwMS (N = 126) and healthy controls (N = 97). All participants performed 3 maximal SLCMJs on a force plate. Temporal, kinetic, and power jump parameters were collected. The Expanded Disability Status Scale (EDSS) was performed on all participants. A repeated measures analysis of covariance (ANCOVA) with age, Body-Mass-Index, and gender as covariates was used.

RESULTS

PwMS with normal muscle strength according to the manual muscle tests showed significantly reduced SLCMJ performance compared to HC. In both groups, jumping performance differed significantly between the dominant and non-dominant leg, with higher effect size for pwMS. A significant interaction effect between leg dominance and group was found for propulsive time, where the pwMS showed an even higher difference between the dominant and non-dominant leg compared to HC. Furthermore, there was a significant small correlation between leg asymmetries and EDSS in pwMS.

CONCLUSION

The study shows that the SLCMJ on a force plate is suitable for the early detection of subclinical lower limb neuromuscular deficits and strength asymmetries in MS.

Biomechanical effects of foot orthoses on jump landing performance: A systematic review

Jumping is involved in a wide range of sports and activities, and foot orthoses (FO) are suggested to enhance performance and prevent injury. The aim of this systematic review was to investigate whether using FO with different modifications affects jump landing biomechanics and improves performance in healthy individuals. The search strategy included 7 databases that identified 19 studies. The study quality was evaluated using a modified Downs and Black index. The primary outcome measures were joint kinematics, kinetics, muscle activity, vertical jump height, and horizontal jump distance. Our findings indicated that incorporating arch support with a rearfoot post and softer forefoot region into FO may improve several biomechanical variables during jump landing activities. Improvements in vertical ground reaction force loading rates, knee and ankle kinematics, and muscle cocontraction during jumping with FO could enhance jumping performance. In addition, improvements in hip, knee, ankle, and tibial kinematics and vertical ground reaction force loading rates during landing could reduce impact forces and related injuries. Although a limited number of studies have addressed the effects of FO on vertical jump height and horizontal jump distance, inserting such FO inside shoes with optimum bending stiffness could facilitate jumping performance. A rigorous exploration of the effect and mechanism of FO designs on jumping performance could benefit jumping-related activities and prevent ankle and knee injuries.

Analysis of Rate of Force Development as a Vertical Jump Height Predictor

Purpose: Many researchers and coaches hold that the ability to generate force rapidly is an important factor in athletic performance. This concept is often studied by analyzing the rate of ground reaction force development (RFD) during vertical jumps; however, many such studies disagree on whether estimates of RFD are true predictors of vertical jump height, have limited sample sizes, and have not employed multiple regression analysis. Therefore, the purpose of the study was to assess the utility of RFD as a predictor of vertical jump height. Methods: Forward sequential multiple regression models were performed using kinematic, kinetic, and demographic variables from a database of maximal countermovement vertical jumps collected via motion capture system from 2,258 NCAA Division I athletes. Results: Peak RFD was a significant bivariate predictor of vertical jump height (r = 0.408, p < .001). However, when other variables were included in the prediction model the partial variance in vertical jump height accounted for by peak RFD was nearly eliminated (r = -0.051, β = -0.051), but sex (r = 0.246, β = 0.94) and peak ground reaction force (r = 0.503, β = 1.109) emerged as predictors of partial variance in jump height. Furthermore, mediation analysis revealed the direct effect of peak RFD on vertical jump height was only 0.004. Conclusions: Multiple regression analysis enabled by a large sample size suggests Peak RFD may not be uniquely useful as a predictor of vertical jump height during maximal countermovement jumps.

Rationale and Practical Recommendations for Testing Protocols in Female Soccer: A Narrative Review

ABSTRACT

Beato, M, Datson, N, Anderson, L, Brownlee, T, Coates, A, and Hulton, A. Rationale and practical recommendations for testing protocols in female soccer: A narrative review. J Strength Cond Res 37(9): 1912-1922, 2023-The aim of this narrative review is to evaluate the presented literature on tests (aerobic, speed, changes of direction [COD], strength, power, jump, and anthropometry) of the varied components of female soccer and to draw attention to the most suitable protocols to allow practitioners to accurately track players' fitness status. The 2 most common field tests used to assess aerobic fitness are the Yo-Yo intermittent test (level 1 and level 2) and the 30-15 intermittent fitness test because of an ability to measure multiple players at once with a soccer-specific intermittent profile. The sprinting performance can be assessed on distances of <30 m; however, longer distances (e.g., 40 m) allow for achieving peak speed (flying sprint test), which can be assessed using global navigation satellite system. Changes-of-direction capacity has been found to be an important component of players testing and training programs, although there is no "gold standard" to assess COD or repeated sprint ability performance in female players. Lower-limb power can be assessed using jump tests that can use force platforms, jump mats, and optoelectronic devices, while maintaining a good reliability. Several in-direct tests are currently available for assessing anthropometry parameters, such as skinfold thickness, hydrodensitometry, and ultrasound. However, dual-energy x-ray absorptiometry is the most valid and reliable method for assessing body composition in team sport athletes, with the addition of bone health that is a key measure in female athletes. In conclusion, the evidence reported in this review will be able to aid practitioners, coaches, and researchers to decide which tests meet the requirements of their environment.

Analysis on the characteristics and relationships of lower limbs strength and power of sailors in different positions and levels

Hikers and trapeze sailors are two main Olympic groups based on their specific role during sail racing. This study was to analyze the characteristics and relationships of lower limbs strength and power of hikers and trapeze sailors with different levels. Forty-five hikers and trapeze sailors were divided into high-level and low-level groups, respectively. The isokinetic dynamometer was used to measure sailors' lower limbs strength. Concentric and eccentric peak torque (PT) were measured for hamstrings and quadriceps at 60°/s, and isometric knee extensions at 45° knee flexion (0° = full extension). The counter movement jump (CMJ) was performed by Kistler to reflect sailors' lower limbs power. The results showed the hikers had higher quadriceps isometric PT, and male hikers had higher concentric and eccentric PT compared to trapeze sailors (p<0.05). For female sailors, the quadriceps' concentric, eccentric and isometric PT of high-level group were higher than low-level group' (p<0.05). The sailors' conventional and functional H/Q ratio ranged from 0.44 to 0.56 and 0.52 to 0.65, respectively. High-level and low-level groups had no difference in CMJ, which was moderately to strongly correlated with the isokinetic strength (r ranging 0.50-0.81, p<0.01). These findings suggest that long-term training can induce specificity in lower limbs strength of sailors. Hikers have better quadriceps isometric strength compared to trapeze sailors. The quadriceps concentric and eccentric PT can be used as parameters to distinguish between high-level and low-level sailors, but CMJ cannot.

Associations of eccentric force variables during jumping and eccentric lower-limb strength with vertical jump performance: A systematic review

The purpose of this systematic review was to summarize the associations of eccentric force variables during jumping and eccentric lower-limb strength with vertical jump performance. A literature search was conducted in September 2022 using PubMed, Web of Science, and Scopus. Thirteen cross-sectional studies investigating the relationship between eccentric force and strength variables, such as force, rate of force development (RFD), power, time, and velocity, and vertical jump performance, including the jump height, reactive strength index (RSI), and reactive strength index-modified (RSImod), were included in this systematic review. As eccentric strength, variables during the unloading-to-braking phase of countermovement jump (CMJ) (force, RFD, etc.) and the eccentric force of the squat movement and knee joint were included. The CMJ height, RSImod, and drop jump RSI were included to analyze the vertical jump performance. The modified form of the Downs and Black checklist was used to evaluate quality. Associations between the force and RFD during the descending phase of the CMJ and jump height were observed in some studies but not in others, with differences between the studies. Some studies reported associations between the force and/or RFD during the descending phase of the CMJ and RSImod of the CMJ, with no differences among their results. In addition, there are associations of the eccentric forces during squatting and knee extension with the CMJ and the drop jump heights and RSI of the drop jump. The eccentric force variables in the CMJ and RSImod are related; however, their relationship with jump height remains unclear. Furthermore, improved eccentric muscle strength may contribute to vertical jump height because of the associations of the eccentric strength during knee extension and squatting with jump height.

Joint Coordination and Muscle-Tendon Interaction Differ Depending on The Level of Jumping Performance

The countermovement jump is a popular measurement modality to evaluate muscle power in sports and exercise. Muscle power is essential to achieve a high jump, yet the well-coordinated movement of the body segments, which optimizes the stretch-shortening cycle (SSC) effects, is also required. Among the proposed explanations of SSC effects, this study investigated whether the ankle joint kinematics, kinetics, and muscle-tendon interaction depend on the level of jump skill and the jump task. Sixteen healthy males were grouped as a function of their jump height (High jumpers; greater than 50 cm, Low jumpers; less than 50 cm). They were instructed to jump with two intensities; light effort (20 % of their height) and maximal effort. Joint kinematics and kinetics of the lower limbs were analyzed using a 3-dimensional motion analysis system. The muscle-tendon interaction was investigated using B-mode real-time ultrasonography. As the jump intensity increased, all participants jumped with increased joint velocity and power. However, the high jumper shows less fascicle shortening velocity (-0.2 ± 0.1 m/s) than the low jumper group (-0.3 ± 0.1 m/s) and greater tendon velocity, which indicated the capability of elastic energy recoil. In addition, the delayed onset time of ankle extension in the high jumper implies better use of the catapult mechanism. The findings of this study showed that the muscle-tendon interaction differs depending on the jump skill level, suggesting a more efficient neuromuscular control in skilled jumpers.

A Minimal Sensor Inertial Measurement Unit System Is Replicable and Capable of Estimating Bilateral Lower-Limb Kinematics in a Stationary Bodyweight Squat and a Countermovement Jump

This study aimed to validate a 7-sensor inertial measurement unit system against optical motion capture to estimate bilateral lower-limb kinematics. Hip, knee, and ankle sagittal plane peak angles and range of motion (ROM) were compared during bodyweight squats and countermovement jumps in 18 participants. In the bodyweight squats, left peak hip flexion (intraclass correlation coefficient [ICC] = .51), knee extension (ICC = .68) and ankle plantar flexion (ICC = .55), and hip (ICC = .63) and knee (ICC = .52) ROM had moderate agreement, and right knee ROM had good agreement (ICC = .77). Relatively higher agreement was observed in the countermovement jumps compared to the bodyweight squats, moderate to good agreement in right peak knee flexion (ICC = .73), and right (ICC = .75) and left (ICC = .83) knee ROM. Moderate agreement was observed for right ankle plantar flexion (ICC = .63) and ROM (ICC = .51). Moderate agreement (ICC > .50) was observed in all variables in the left limb except hip extension, knee flexion, and dorsiflexion. In general, there was poor agreement for peak flexion angles, and at least moderate agreement for joint ROM. Future work will aim to optimize methodologies to increase usability and confidence in data interpretation by minimizing variance in system-based differences and may also benefit from expanding planes of movement.

Comparing the Effects of Long-Term vs. Periodic Inclusion of Isometric Strength Training on Strength and Dynamic Performances

ABSTRACT

Lum, D, Joseph, R, Ong, KY, Tang, JM, and Suchomel, TJ. Comparing the effects of long-term vs. periodic inclusion of isometric strength training on strength and dynamic performances. J Strength Cond Res 37(2): 305-314, 2023-This study compared the effects of including isometric strength training (IST) for consecutive 24 weeks (CIST) against a periodic inclusion (PIST) of this mode of training on strength and dynamic performances. Twenty-four floorball athletes (age: 23 ± 2.7 years, stature: 1.74 ± 2.08 m, and body mass: 72.7 ± 14.4 kg) were randomly assigned to the control (CON), CIST, or PIST group. Athletes completed 20-m sprint, countermovement jump (CMJ), and isometric midthigh pull (IMTP) during pre-test and were tested on weeks 6, 12, 18, and 24. All groups performed a similar strength training program twice per week. However, 2 sets of squats were replaced with isometric squat in CIST for all 24 weeks but only on weeks 1-6 and 13-18 for PIST. A significant main effect for time was observed for 5-, 10-, and 20-m sprint time, CMJ height, peak force, peak power, time to take-off, modified reactive strength index, IMTP peak force, relative peak force, and force at 200 milliseconds ( p = <0.001-0.037). Isometric strength training for 24 consecutive weeks resulted in greater improvement in 5-m sprint time than CON at week 24 ( p = 0.024, g = 1.17). Both CIST and PIST resulted in greater improvements in 10-m sprint time than CON at various time points ( p = 0.007-0.038 and 0.038, g = 1.07-1.44 and 1.18, respectively). Isometric strength training for 24 consecutive weeks and PIST resulted in greater improvements in 20-m sprint time than CON at week 6 ( p = 0.007 and 0.025, g = 1.65 and 1.40, respectively). The results showed that the inclusion of IST resulted in greater improvements in sprint performance than CON but no significant difference in all measured variables with PIST.

Influence of lower-limb muscular and tendon mechanical properties and strength on countermovement jump performance

BACKGROUND

The aim of the study is to examine the relationship between measures of muscle and tendon mechanical properties and strength on countermovement jump (CMJ) performance.

METHODS

Twenty-six physically active participants (males; N.=16: females; N.=10) were tested. Testing comprised of measuring the mechanical properties of lower limb muscles and tendons using myotonometry, isometric and isokinetic knee extensor strength through dynamometry, and CMJ's with a force platform.

RESULTS

Large positive correlations were observed between CMJ jump height and Achilles tendon stiffness (N/m) (r=0.56) and Achilles tendon tone (Hz) (r=0.553). Large negative correlations were found between CMJ height and Achilles tendon elasticity (r=-0.658), and Achilles tendon relaxation (r=-0.572), and Achilles tendon creep (r=-0.589). Large correlations (r=0.592 to 0.659) were observed between CMJ height and all measures of isometric and isokinetic dynamometry measures. Achilles tendon stiffness, elasticity level and relaxation, and isokinetic peak concentric torque (N.m) explained 63% of this variance.

CONCLUSIONS

Greater stiffness of the Achilles tendon may improve CMJ performance due to the improved transfer of concentric and eccentric force of the knee extensor muscles. Practitioners need to implement specific interventions to target increasing Achilles tendon stiffness to improve countermovement jump performance.

Flywheel eccentric overload exercises versus barbell half squats for basketball players: Which is better for induction of post-activation performance enhancement?

OBJECTIVE

This study compared the post-activation performance enhancement (PAPE) effects of a flywheel eccentric overload (FEOL) exercise and barbell half squats (BHS) on countermovement jump (CMJ) and 30 m sprint performance.

METHODS

Twelve male collegiate competitive basketball players were enrolled in this study and they implemented two training protocols: barbell half squat (BHS) and flywheel eccentric overload (FEOL) training. The BHS protocol included three intensities of load: low (40% 1RM), medium (60% 1RM), and high (80% 1RM), with each intensity consisting of 5 sets of 3 repetitions. The FEOL protocol included three inertia intensities: low (0. 015 kg∙m2), medium (0.035 kg∙m2), and high (0.075 kg∙m2), with each intensity consisting of 3 sets of 6 repetitions. The measurement time points were before training (baseline) and at 3, 6, 9, and 12 minutes after training. A two-stage (stage-I and stage-II) randomized crossover design was used to determine the acute effects of both protocols on CMJ and sprint performance.

RESULTS

At each training intensity, the jump height, jump peak power output (PPO), jump impulse and 30m sprint speed at 3, 6, 9, and 12 minutes after BHS and FEOL training did not change significantly compared to the baseline. A 2-way ANOVA analysis indicated significant main effects of rest intervals on jump height, jump PPO, and jump impulse, as well as 30m sprint speed. The interaction of the Time × protocol showed a significant effect on jump height between BHS and FEOL groups at high intensity in stage-I (F = 3.809, p = 0.016, df = 4) and stage-II (F = 3.044, p = 0.037, df = 4). And in high training intensity, the jump height at 3 (7.78 ± 9.90% increase, ES = 0.561), 6 (8.96 ± 12.15% increase, ES = 0.579), and 9 min (8.78 ± 11.23% increase, ES = 0.608) were enhanced in I-FEOL group compared with I-BHS group (F = 3.044, p = 0.037, df = 4). In stage-II, the impulse and sprint speed of the FEOL group were significantly higher than those of the BHS group at 6, 9, and 12 min under low (FEOL = 0.015kg∙m2, BHS = 40%1RM), medium(FEOL = 0.035kg∙m2, BHS = 60%1RM), and high (FEOL = 0.075kg∙m2, BHS = 80%1RM) intensities. Furthermore, the sprint speed of the two training protocols did not change at different time points. The interaction of Time × training intensity showed lower sprint speeds in the II-BHS group at a high intensity (BHS = 80%1RM) compared to low (BHS = 40%1RM) and medium (BHS = 60%1RM) training intensities, especially at 9 min and 12 min rest intervals.

CONCLUSION

Although barbell half squat training and flywheel eccentric overload training did not provide a significant PAPE effect on explosive power (CMJ and sprint) in male basketball players, FEOL training showed a better potential effect on enhanced CMJ jump performance at the high training intensity.

Joint-level determinants of the dynamic strength index: implications for testing and monitoring

The aims of this study were to determine the associations and differences between the traditional dynamic strength index (DSIGRF, calculated from ground reaction force [GRF] data) and joint-level dynamic strength indices (DSINJM, calculated from net joint moment [NJM] data). Eight female NCAA Division I lacrosse players performed three maximal effort isometric mid-thigh pulls (IMTP) and countermovement jumps (CMJ). GRF and motion capture data were recorded and used to calculate hip, knee, and ankle NJM. The ratio between peak forces during the IMTP and CMJ tests was used to calculate the DSIGRF and the ratio of peak NJM was used to calculate ankle, knee, and hip DSINJM. Associations and differences between DSIGRF and DSINJM were examined with Pearson's correlation coefficients, paired t-tests and Hedge's g effect sizes. The results showed that only the hip DSINJM was correlated with DSIGRF (hip: p = 0.037; r = 0.738). In addition, athletes exhibited significantly greater DSINJM than DSIGRF. Although these results suggest DSIGRF are associated with hip DSINJM, the fact that joint-level DSINJM were generally greater than DSIGRF suggests the ratio between peak NJM during the CMJ and IMTP may not provide intuitive or useful data for strength and conditioning coaches or sport scientists.

Backward Double Integration is a Valid Method to Calculate Maximal and Sub-Maximal Jump Height

The backward double integration method uses one force plate and could calculate jump height for countermovement jumping, squat jumping and drop jumping by analysing the landing phase instead of the push-off phase. This study compared the accuracy and variability of the forward double integration (FDI), backwards double integration (BDI) and Flight Time + Constant (FT+C) methods, against the marker-based rigid-body modelling method. It was hypothesised that the jump height calculated using the BDI method would be equivalent to the FDI method, while the FT+C method would have reduced accuracy and increased variability during sub-maximal jumping compared to maximal jumping. Twenty-four volunteers performed five maximal and five sub-maximal countermovement jumps, while force plate and motion capture data were collected. The BDI method calculated equivalent mean jump heights compared to the FDI method, with only slightly higher variability (2-3 mm), and therefore can be used in situations where FDI cannot be employed. The FT+C method was able to account for reduced heel-lift distance, despite employing an anthropometrically scaled heel-lift constant. However, across both sub-maximal and maximal jumping, it had increased variability (1.1 cm) compared to FDI and BDI and should not be used when alternate methods are available.

The effect of flywheel training on strength and physical capacities in sporting and healthy populations: An umbrella review

The aim of this umbrella review was to provide a detailed summary of how flywheel training enhances strength and physical capacities in healthy and athletic populations. The eleven reviews included were analyzed for methodological quality according to the Assessing the Methodological Quality of Systematic Review 2 (AMSTAR 2) and the Grading of Recommendations Assessment, Development and Evaluation (GRADE) criteria. Two were systematic reviews, six were systematic reviews with meta-analyses and three were narrative reviews. Although the included reviews support use of flywheel training with athletic and healthy populations, the umbrella review highlights disparity in methodological quality and over-reporting of studies (38 studies were included overall). Flywheel post-activation performance enhancement protocols can effectively enhance strength and physical capacities acutely with athletes and healthy populations. All relevant reviews support flywheel training as a valid alternative to traditional resistance training for enhancing muscular strength, power, and jump performance with untrained and trained populations alike. Similarly, reviews included report flywheel training enhances change of direction performance—although conclusions are based on a limited number of investigations. However, the reviews investigating the effect of flywheel training on sprint performance highlight some inconsistency in attained improvements with elite athletes (e.g., soccer players). To optimize training outcomes, it is recommended practitioners individualize (i.e., create inertia-power or inertia-velocity profiles) and periodize flywheel training using the latest guidelines. This umbrella review provides an analysis of the literature’s strengths and limitations, creating a clear scope for future investigations.

Effects of Task Constraints on Countermovement Jump Kinematics Following a Short-Term Training

In previous studies, the acute effects of movement constraints on the countermovement jump performance are investigated; however, the longitudinal effects of implementing the constraint in a training regimen are not well studied. The purpose of this study was to examine the phenomenon of motor learning development due to application of task constraint in a training regimen following 6 weeks of training. Forty-five healthy adult males were randomly assigned to a control or one of two experimental constraint training groups (i.e., no arm swing or restricted knee flexion). Pre- and posttraining jump height and kinematic variables of six maximum effort countermovement jumps were compared longitudinally within the groups, and also compared between the groups. The findings of this study indicated that jump height significantly increased in all the groups while in the unrestricted control group it was increased greater than the experimental conditions (21% compared with 12% and 5.5%). However, the applied task constraints significantly improved some of the contributors to jump performance, establishing specific adaptation of kinematic variables to the constraint training. Therefore, constraint training approach could be suggested in case of demanding specific adaptation of kinematic variables of countermovement jump in a training regimen.

Factors influencing the jump momentum - sprint momentum correlation: a data simulation

Jump take-off momentum has previously been proposed as an alternative test to predict sprint momentum. This study used a data simulation to replicate and systematically investigate relationships reported in previous studies between body mass, vertical jump performance, and sprint performance. Results were averaged for 1000 simulated data sets in each condition, and the effects of various parameters on correlations between jump momentum and sprint momentum were determined. The ability of jump take-off momentum to predict sprint momentum is greatest under relatively high inter-individual variation in body mass and relatively low inter-individual variation in jump height. This is largely due to the increased emphasis on body mass in these situations. Even under zero or a small negative (r = -0.30) correlation between jump height and sprint velocity, the correlation between the two momenta remained very large (r ≥ 0.76) on average. There were no investigated conditions under which jump momentum was most frequently a significantly (p < 0.05) greater predictor of sprint momentum compared to simply using body mass alone. Furthermore, between-individual correlations should not be used to make inferences or predictions for within-individual applications (e.g. predicting or evaluating the effects of a longitudinal training intervention). It is recommended that any rationale for calculating and/or monitoring jump take-off momentum should be separate from its ability to predict sprint momentum. Indeed, body mass alone may be a better predictor of sprint momentum.

Hip Abductor and Adductor Rate of Torque Development and Muscle Activation, but Not Muscle Size, Are Associated With Functional Performance

Understanding the physiological variables that contribute to a functional task provides important information for trainers and clinicians to improve functional performance. The hip abductors and adductors muscles appear to be important in determining the performance of some functional tasks; however, little is known about the relationship of the hip abductor/adductors muscle strength, activation, and size with functional performance. This study aimed to investigate the relationship of maximum torque, rate of torque development (RTD), rate of activation (RoA), and muscle thickness of the hip abductors [tensor fascia latae (TFL) and gluteus medius (GM)] and adductor magnus muscle with the Four Square Step Test (FSST) and the two-leg hop test in healthy young adults. Twenty participants (five males) attended one testing session that involved ultrasound image acquisition, maximal isometric voluntary contractions (hip abduction and hip adduction) while surface electromyography (EMG) was recorded, and two functional tests (FSST and two-leg side hop test). Bivariate correlations were performed between maximum voluntary torque (MVT), RTD at 50, 100, 200, and 300ms, RoA at 0-50, 0-100, 0-200, and 0-300, and muscle thickness with the dynamic stability tests. For the hip abduction, MVT (r=-0.455, p=0.044) and RTD₃₀₀ (r=-0.494, p=0.027) was correlated with the FSST. GM RoA₅₀ (r=-0.481, p=0.032) and RoA₁₀₀ (r=-0.459, p=0.042) were significantly correlated with the two-leg side hop test. For the hip adduction, there was a significant correlation between the FSST and RTD₃₀₀ (r=-0.500, p=0.025), while the two-leg side hop test was correlated with RTD₂₀₀ (r=0.446, p=0.049) and RTD₃₀₀ (r=0.594, p=0.006). Overall, the ability of the hip abductor and adductor muscles to produce torque quickly, GM rapid activation, and hip abductor MVT is important for better performance on the FSST and two-leg hop tests. However, muscle size appears not to influence the same tests.

Effect of Postactivation Potentiation After Medium vs. High Inertia Eccentric Overload Exercise on Standing Long Jump, Countermovement Jump, and Change of Direction Performance

ABSTRACT

Beato, M, De Keijzer, KL, Leskauskas, Z, Allen, WJ, Dello Iacono, A, and McErlain-Naylor, SA. Effect of postactivation potentiation after medium vs. high inertia eccentric overload exercise on standing long jump, countermovement jump, and change of direction performance. J Strength Cond Res 35(9): 2616-2621, 2021-This study aimed to evaluate the postactivation potentiation (PAP) effects of an eccentric overload (EOL) exercise on vertical and horizontal jumps and change of direction (COD) performance. Twelve healthy physically active male subjects were involved in a crossover study. The subjects performed 3 sets of 6 repetitions of EOL half squats for maximal power using a flywheel ergometer. Postactivation potentiation using an EOL exercise was compared between a medium (M-EOL) vs. high inertia (H-EOL) experimental condition. Long jump (LJ) was recorded at 30 seconds, 3, and 6 minutes after both EOL exercises and compared with baseline values (control). The same procedure was used to assess countermovement jump (CMJ) height and peak power and 5-m COD test (COD-5m). A fully Bayesian statistical approach to provide probabilistic statements was used in this study. Long jump performance reported improvements after M-EOL and H-EOL exercise (Bayes factor [BF10] = 32.7, strong; BF10 = 9.2, moderate), respectively. Countermovement jump height (BF10 = 135.6, extreme; BF10 > 200, extreme), CMJ peak power (BF10 > 200, extreme; BF10 = 56.1, very strong), and COD-5m (BF10 = 55.7, very strong; BF10 = 16.4, strong) reported improvements after M-EOL and H-EOL exercise, respectively. Between analysis did not report meaningful differences in performance between M-EOL and H-EOL exercises. The present outcomes highlight that PAP using an EOL (M-EOL and H-EOL) improves LJ, CMJ height, CMJ peak power, and COD-5m in male athletes. The optimal time window for the PAP effect was found for both EOL conditions from 3 to 6 minutes. However, M-EOL and H-EOL produce similar PAP effect on LJ, CMJ, and COD-5m tasks.

Association and Agreement between Reactive Strength Index and Reactive Strength Index-Modified Scores

Since the reactive strength index (RSI) and reactive strength index-modified (RSI-mod) share similar nomenclature, they are commonly referred as interchangeable measures of agility in the sports research literature. The RSI and RSI-mod are most commonly derived from the performance of depth jumping (DJ) and countermovement jumping (CMJ), respectively. Given that DJ and CMJ are plyometric movements that differ materially from biomechanical and neuromotor perspectives, it is likely that the RSI and RSI-mod measure distinct aspects of neuromuscular function. The purpose of this investigation was to evaluate the association and agreement between RSI and RSI-mod scores. A mixed-sex sample of NCAA division I basketball athletes (n = 21) and active young adults (n = 26) performed three trials of DJ from drop heights of 0.51, 0.66, and 0.81 m and three trials of countermovement jumping. Using 2-dimensional videography and force platform dynamometry, RSI and RSI-mod scores were estimated from DJ and CMJ trials, respectively. Linear regression revealed moderate associations between RSI and RSI-mod scores (F = 11.0–38.1; R² = 0.20–0.47; p < 0.001–0.001). Bland–Altman plots revealed significant measurement bias (0.50–0.57) between RSI and RSI-mod scores. Bland–Altman limit of agreement intervals (1.27–1.51) were greater than the mean values for RSI (0.97–1.05) and RSI-mod (0.42) scores, suggesting poor agreement. Moreover, there were significant performance-dependent effects on measurement bias, wherein the difference between and the mean of RSI and RSI-mod scores were positively associated (F = 77.2–108.4; R² = 0.63–0.71; p < 0.001). The results are evidence that the RSI and RSI-mod cannot be regarded as interchangeable measures of reactive strength.

Comparing power hitting kinematics between skilled male and female cricket batters

Organismic, task, and environmental constraints are known to differ between skilled male and female cricket batters during power hitting tasks. Despite these influences, the techniques used in such tasks have only been investigated in male cricket batters. This study compared power hitting kinematics between 15 male and 15 female batters ranging from university to international standard. General linear models were used to assess the effect of gender on kinematic parameters describing technique, with height and body mass as covariates. Male batters generated greater maximum bat speeds, ball launch speeds, and ball carry distances than female batters on average. Male batters had greater pelvis-thorax separation in the transverse plane at the commencement of the downswing (β = 1.14; p = 0.030) and extended their lead elbows more during the downswing (β = 1.28; p = 0.008) compared to female batters. The hypothesised effect of gender on the magnitude of wrist uncocking during the downswing was not observed (β = -0.14; p = 0.819). The causes of these differences are likely to be multi-factorial, involving aspects relating to the individual players, their history of training experiences and coaching practices, and the task of power hitting in male or female cricket.

The difference between squat jump and countermovement jump in 770 male and female participants from different sports

Traditionally, a larger difference between countermovement (CMJ) and squat jump (SJ) was seen as beneficial, as it reflects the ability to utilize the stretch-shortening cycle. However, strong arguments have been made that this might not always be the case, as larger differences between the jumps could also suggest higher muscle-tendon slack, or poor capability to take this slack up quickly. The purpose of this study was to explore SJ and CMJ, as well as the CMJ to SJ difference (CMJSJ_Diff) in 9 groups of young athletes. In total, 712 athletes from various disciplines (mean age range: 15.7-36.3 years) and 58 physical education students (mean age: 19.6 years) participated in the study. The major finding of this study was that the groups that showed better SJ and CMJ performance did not show the larger CMJSJ_Diff. For instance, SJ and CMJ heights were highest in short-distance runners and lowest in long-distance runners, while the largest and smallest CMJSJ_Diff was shown in physical education students and speed skaters, respectively. Male athletes had a higher CMJSJ_Diff than female athletes, but the difference was very small. While a larger CMJSJ_Diff has been traditionally associated viewed as positive, our results could indicate both superior ability to utilize the stretch-shortening cycle, as well as poor ability of rapid force development and excessive muscle slack. Further studies are needed to directly investigate the associations between CMJSJ_Diff and indicators of athletic performance.

Female Adolescent Soccer Players Utilize Different Neuromuscular Strategies Between Limbs During the Propulsion Phase of a Lateral Vertical Jump

BACKGROUND

Multiplanar dynamic stability is an important unilateral function in soccer performance but has been scarcely examined in female soccer players. The lateral vertical jump task assesses unilateral functional performance, and energy generation contribution examines how each joint (hip, knee, ankle) contributes to the vertical component of the vertical jump phase to measure inter- and intra-limb differences.

PURPOSE

To examine dominant versus non-dominant limb performance using energy generation contribution of the hip, knee, and ankle during the vertical jump component of the lateral vertical jump.

STUDY DESIGN

Cross-sectional observational study.

METHODS

Seventeen healthy, adolescent female soccer players (age 13.4±1.7 years; height 160.6±6.0 cm; mass 53.1±8.2 kg) participated. Quadriceps strength was measured via isokinetic dynamometry. Energy generation contribution (measured from maximal knee flexion to toe off) and vertical jump height were measured during the vertical component of the lateral vertical jump.

RESULTS

There was no significant difference between limbs for quadriceps strength (p=0.64), jump height (p=0.59), or ankle energy generation contribution (p=0.38). Energy generation contribution was significantly greater in the dominant hip (dominant 29.7±8.6%, non-dominant 18.4±6.3%, p<0.001) and non-dominant knee (dominant 22.8±6.8%, non-dominant 36.2±8.5%, p<0.001).

CONCLUSION

High demand on coordination and motor control during the lateral vertical jump and inherent limb dominance may explain different intra-limb strategies for task performance despite jump height symmetry. Non-dominant affinity for stability and dominant compensatory performance may neutralize potential asymmetries. Implications for symmetry in observable outcomes such as jump height must consider underlying internal asymmetries.

LEVELS OF EVIDENCE

3B.

CLINICAL RELEVANCE

Symmetrical findings on functional tasks have underlying internal asymmetries observed here in female adolescent soccer players. The lateral vertical jump may highlight these internal asymmetries (hip- versus knee-dominant movement strategies) due to the high coordinative demand to perform the task. Clinicians should be cognizant of underlying, potentially inherent, asymmetries even when observing functional symmetry in a task.

WHAT IS KNOWN ABOUT THE SUBJECT

Female adolescent soccer players are a high-risk cohort for sustaining anterior cruciate ligament injuries. Limb dominance may play a role in the performance of functional tasks, and limb dominance in soccer players is quite specialized: the dominant limb is the preferred kicking limb, while the non-dominant limb is the preferred stabilizing limb (plant leg). Functional performance in female soccer players has been studied in kicking, dribbling, sprinting, change of direction, and jumping - however, these tasks were measured independent of limb dominance. It remains to be seen how unilateral functional tasks may be affected by limb dominance in female adolescent soccer players.

WHAT THIS STUDY ADDS TO EXISTING KNOWLEDGE

This study provides data on functional performance relative to limb dominance in female adolescent soccer players, and captures the lateral vertical jump task in both inter- and intra-limb measures. This highlights that intra-limb strategies to perform a coordinated motor task may be different between limbs, herein attributed to limb dominance. Even if gross motor outputs between limbs are symmetrical (i.e. jump height), the underlying movement strategies to achieve that output may be different (hip- versus knee-dominant movement strategies). These findings are important to research on functional performance measures related to attaining between-limb symmetry, as measures of energy generation contribution open the door for a more thorough understanding of joint-by-joint intra-limb contributions during a functional task.

Analyses of Countermovement Jump Performance in Time and Frequency Domains

This study aimed to analyze counter-movement jump (CMJ) performance in time and frequency domains. Fortyfour Division I American football players participated in the study. Kinetic variables were collected from both dominant and non-dominant legs using two force plates. Normalized peak power, normalized net impulse, and normalized peak force significantly correlated with jump height (r = .960, r = .998, r = .725, respectively with p < .05). The mean frequency component was significantly correlated with CMJ performance (r = .355 with p < .05). The reliability of the frequency variables was higher than the time domain variables. Frequency domain variables showed weaker correlations with jump height compared with time domain variables. Frequency domain analysis provides frequency components, which represent the rate of energy transmission from the eccentric phase to the end of the push-off phase. Frequency component information may provide additional information for the analyses of CMJ performance for athletes.

Post Flywheel Squat Potentiation of Vertical and Horizontal Ground Reaction Force Parameters during Jumps and Changes of Direction

(1) Background: The aim of the study was to determine the post-activation performance enhancement (PAPE) of vertical and horizontal ground reaction force parameters during jumps and change of direction following flywheel squat exercise using two different flywheel inertias. (2) Methods: Eleven male athletes performed a countermovement jump (CMJ), standing broad jump (SBJ), and “modified 505” change of direction (COD) in a control condition and 6 minutes following three sets of six repetitions of flywheel half squats at one of two inertias (0.029 kg·m² and 0.061 kg·m²). Peak directional ground reaction force, power, and rate of force development were calculated for each test. (3) Results: Higher inertia flywheel squats were able to acutely enhance CMJ peak vertical force (Bayes Factor (BF₁₀) = 33.5, very strong; δ = 1.66; CI: 0.67, 2.70), whereas lower inertia flywheel squats were able to acutely enhance CMJ peak vertical power (BF₁₀ = 3.65, moderate; δ = 0.93; CI: 0.11, 1.88). The vertical squat exercise induced no PAPE effect on resultant SBJ or horizontal COD ground reaction force parameters, nor were any differences observed between the inertias. (4) Conclusions: Researchers and practitioners should consider the kinetic and kinematic correspondence of a pre-load stimulus to the subsequent sport-specific activity (i.e., flywheel squat to CMJ).

Post-activation performance enhancement (PAPE) after a single bout of high-intensity flywheel resistance training

This study investigated the post-activation performance enhancements (PAPE) induced by a high-intensity single set of accentuated eccentric isoinertial resistance exercise on vertical jump performance. Twenty physically active male university students performed, in randomized counterbalanced order, two different conditioning activities (CA) after a general preestablished warm-up: a conditioning set of 6 maximum repetitions at high intensity (i.e., individualized optimal moment of inertia [0.083 ± 0.03 kg·m^-2]) of the flywheel half-squat exercise in the experimental condition, or a set of 6 maximal countermovement jumps (CMJ) instead of the flywheel exercise in the control condition. CMJ height, CMJ concentric peak power and CMJ concentric peak velocity were assessed at baseline (i.e., 3 minutes after the warm-up) and 4, 8, 12, 16 and 20 minutes after the CA in both experimental and control protocols. Only after the experimental protocol were significant gains in vertical jump performance (p < 0.05, ES range 0.10–1.34) at 4, 8, 12, 16 and 20 minutes after the CA observed. In fact, the experimental protocol showed greater (p < 0.05) CMJ height, concentric peak power and concentric peak velocity enhancements compared to the control condition. In conclusion, a single set of high-intensity flywheel training led to PAPE in CMJ performance after 4, 8, 12, 16 and 20 minutes in physically active young men.

The relationship between isometric mid-thigh pull variables and athletic performance measures: empirical study of English professional soccer players and meta-analysis of extant literature

BACKGROUND

There is currently limited evidence available to support the use of the isometric mid-thigh pull (IMTP) within professional soccer. The aim of this study was to analyze the association between IMTP variables, with common markers of athletic performance capability.

METHODS

Eleven professional development soccer players (age: 20±2 years, stature: 1.82±0.10 m, mass: 76.4±12.8 kg) performed IMTP, 5 m and 10 m accelerations, maximal sprint speed (MSS), countermovement jump (CMJ), and the 505 change of direction test (COD).

RESULTS

Relative and absolute peak force (PF) and force at 50, 100, 150 and 200 ms values were measured during the IMTP. Relative F150, F200, PF displayed large to very large correlations with MSS (r=0.51, r=0.66, and r=0.76 respectively), while absolute PF also displayed a large correlation with MSS (r=0.57). Relative and absolute PF showed large correlations with CMJ height (r=0.54 and r=0.55 respectively). Relative F150 and F200 highlighted large correlations with COD ability (r=-0.68 and r=-0.60 respectively). Relative F200 and PF had a large negative correlation with 10 m acceleration (r=-0.55 and r=-0.53 respectively).

CONCLUSIONS

This study provides an important contribution to knowledge within the area of IMTP testing in professional soccer by evidencing the prominence of the isometric force generating capacity as an underpinning factor in relation to athletic capability.

An Intramuscular Injection of Mixed Testosterone Esters Does Not Acutely Enhance Strength and Power in Recreationally Active Young Men

Purpose: Limited data are available on the acute performance-enhancing effects of single-dose administration of testosterone in healthy humans. Studies of testosterone administrations to healthy humans are rare due to the difficult nature and necessity of close clinical monitoring. However, our unique physiological experimental facilities combined with close endocrinological collaboration have allowed us to safely complete such a study. We tested the hypothesis that an intramuscular injection of 250 mg mixed testosterone esters (TEs) enhances physical performance in strength and power exercises acutely, measured 24 h after injection. Additionally, we investigated whether the basal serum testosterone concentration influences the performance in countermovement jump (CMJ), 30-s all out cycle sprint, and one-arm isometric elbow flexion.

Methods: In a randomized, double-blind, placebo-controlled design, 19 eugonadal men received either a TE (n = 9, 23 ± 1 years, 183 ± 7 cm, 83 ± 10 kg) or a PLA (n = 10, 25 ± 2 years, 186 ± 6 cm, 82 ± 14 kg) injection. Hormonal levels and the performance in CMJ, 30-s all out cycle sprint, and one-arm isometric elbow flexion were measured before and 24 h after injection.

Results: Firstly, an intramuscular injection of 250 mg mixed TEs did not enhance the vertical jump height in a CMJ test, peak power, mean power, and fatigue index in a 30-s all-out cycle sprint or rate of force development and maximal voluntary contraction in a one-arm isometric elbow flexion 24 h post-injection. Secondly, baseline testosterone levels appeared not to influence performance in strength and power exercises to a large extent in healthy, recreationally active young men.

Conclusion: A single intramuscular injection of 250 mg mixed TEs has no acute ergogenic effects on strength and power performance in recreationally active, young men. This novel information has implication for basic physiological understanding. Whether the same applies to an elite athlete population remains to be determined. If so, this would have implications for anti-doping efforts aiming to determine the most cost-efficient testing programs.

Different Movement Strategies in the Countermovement Jump Amongst a Large Cohort of NBA Players

Previous research has demonstrated large amounts of inter-subject variability in downward (unweighting & braking) phase strategies in the countermovement jump (CMJ). The purpose of this study was to characterize downward phase strategies and associated temporal, kinematic and kinetic CMJ variables. One hundred and seventy-eight NBA (National Basketball Association) players (23.6 ± 3.7 years, 200.3 ± 8.0 cm; 99.4 ± 11.7 kg; CMJ height 68.7 ± 7.4 cm) performed three maximal CMJs. Force plate and 3D motion capture data were integrated to obtain kinematic and kinetic outputs. Afterwards, athletes were split into clusters based on downward phase characteristics (k-means cluster analysis). Lower limb joint angular displacement (i.e., delta flexion) explained the highest portion of point variability (89.3%), and three clusters were recommended (Ball Hall Index). Delta flexion was significantly different between clusters and players were characterized as "stiff flexors", "hyper flexors", or "hip flexors". There were no significant differences in jump height between clusters (p > 0.05). Multiple regression analyses indicated that most of the jumping height variance was explained by the same four variables, (i.e., sum concentric relative force, knee extension velocity, knee extension acceleration, and height) regardless of the cluster (p < 0.05). However, each cluster had its own unique set of secondary predictor variables.

Effects of High-Intensity Interval Training in Hypoxia on Taekwondo Performance

PURPOSE

To evaluate the effects of a 6-week taekwondo-specific high-intensity interval training (HIIT) in simulated normobaric hypoxia on physical fitness and performance in taekwondoists.

METHODS

Eighteen male and female black-belt taekwondoists trained twice a week for 6 weeks in normoxia or in hypoxia (FiO2 = 0.143 O2). The HIIT was composed of specific taekwondo movements and simulated fights. Body composition analyses and a frequency speed of kick test during 10 seconds (FSKT10s) and 5 × 10 seconds (FSKTmult), countermovement jump (CMJ) test, Wingate test, and an incremental treadmill test were performed before and after training. Blood lactate concentrations were measured after the FSKTmult and Wingate tests, and a fatigue index during the tests was calculated.

RESULTS

A training effect was found for FSKT10s (+35%, P < .001), FSKTmult (+32%, P < .001), and fatigue index (-48%, P = .002). A training effect was found for CMJ height (+5%, P = .003) during the CMJ test. After training, CMJ height increased in hypoxia only (+7%, P = .005). No effect was found for the parameters measured during Wingate test. For the incremental treadmill test, a training effect was found for peak oxygen consumption (P = .002), the latter being 10% lower after than before training in normoxia only (P = .002).

CONCLUSIONS

In black-belt taekwondoists, hypoxic HIIT twice a week for 6 weeks provides tiny additional gains on key performance parameters compared with normoxic HIIT. Whether the trivial effects reported here might be of physiological relevance to improve performance remains debatable and should be tested individually.

Effect of Volume on Eccentric Overload-Induced Postactivation Potentiation of Jumps

PURPOSE

To investigate the postactivation potentiation (PAP) effects of different eccentric overload (EOL) exercise volumes on countermovement-jump (CMJ) and standing-long-jump (LJ) performance.

METHODS

In total, 13 male university soccer players participated in a crossover design study following a familiarization period. Control (no PAP) CMJ and LJ performances were recorded, and 3 experimental protocols were performed in a randomized order: 1, 2, or 3 sets of 6 repetitions of flywheel EOL half-squats (inertia = 0.029 kg·m2). Performance of CMJ and LJ was measured 3 and 6 minutes after all experimental conditions. The time course and magnitude of the PAP were compared between conditions.

RESULTS

Meaningful positive PAP effects were reported for CMJ after 2 (Bayes factor [BF10] = 3.15, moderate) and 3 (BF10 = 3.25, moderate) sets but not after 1 set (BF10 = 2.10, anecdotal). Meaningful positive PAP effects were reported for LJ after 2 (BF10 = 3.05, moderate) and 3 (BF10 = 3.44, moderate) sets but not after 1 set (BF10 = 0.53, anecdotal). The 2- and 3-set protocols resulted in meaningful positive PAP effects on both CMJ and LJ after 6 minutes but not after 3 minutes.

CONCLUSION

This study reported beneficial effects of multiset EOL exercise over a single set. A minimum of 2 sets of flywheel EOL half-squats are required to induce PAP effects on CMJ and LJ performance of male university soccer players. Rest intervals of around 6 minutes (>3 min) are required to maximize the PAP effects via multiple sets of EOL exercise. However, further research is needed to clarify the optimal EOL protocol configurations for PAP response.

Relative contributions and capacities of lower extremity muscles to accelerate the body's center of mass during countermovement jumps

This study aimed to quantify the contributions and capacities of leg muscles to the body's center of mass (COM) acceleration during countermovement jumps (CMJ). Ten basketball players performed CMJ while motion capture and ground reaction force data were recorded and used as inputs to a musculoskeletal model. Contributions and capacities to COM acceleration were quantified with three induced acceleration analyses, which showed that the soleus, gastrocnemii, and vastii muscle groups exhibited the largest potential contribution to COM acceleration. Comparisons among analyses suggested that the soleus and vastii muscle group were operating closest to their maximum capacities.

When Task Constraints Delimit Movement Strategy: Implications for Isolated Joint Training in Dancers

Athletic performance is determined by numerous variables that cannot always be controlled or modified. Due to aesthetic requirements during sports such as dance, body alignment constrains possible movement solutions. Increased power transference around the ankle-joint, coupled with lower hip-joint power, has become a preferential strategy in dancers during leaps and may be considered a dance-specific stretch-shortening cycle (SSC) demand. Newell's theoretical model of interacting constraints includes organismic (or individual), environmental, and task constraints describing the different endogenous and exogenous constraints individuals must overcome for movement and athletic performance. The unique task constraints imposed during dance will be used as a model to justify an isolated joint, single-targeted block progression training to improve physical capacity within the context of motor behavior to enhance dance-specific SSC performance. The suggested ankle-specific block progression consists of isometrics, dynamic constant external resistance, accentuated eccentrics, and plyometrics. Such programming tactics intend to collectively induce tendon remodeling, muscle hypertrophy, greater maximal strength, improved rate of force development, increased motor unit firing rates, and enhanced dynamic movement performance. The current perspective provides a dualistic approach and justification (physiological and motor behavioral) for specific strength and conditioning programming strategies. We propose implementation of a single-targeted block progression program, inspired by Newell's theoretical model of interacting constraints, may elicit positive training adaptations in a directed manner in this population. The application of Newell's theoretical model in the context of a strength and conditioning supports development of musculoskeletal properties and control and is conceptually applicable to a range of athletes.

A Correlational Analysis of Shuttlecock Speed Kinematic Determinants in the Badminton Jump Smash

The forehand jump smash is an essential attacking stroke within a badminton player’s repertoire. A key determinate of the stroke’s effectiveness is post-impact shuttlecock speed, and therefore awareness of critical technique factors that impact upon speed is important to players/coaches. Three-dimensional kinematic data of player, racket and shuttlecock were recorded for 18 experienced players performing maximal effort forehand jump smashes. Joint angles and X-factor (transverse plane pelvis-thorax separation) were calculated at key instants: preparation, end of retraction, racket lowest point, turning point and shuttlecock contact. Peak shoulder, elbow, and wrist joint centre linear velocities, phase durations and jump height were also calculated. Correlational analyses were performed with post-impact shuttlecock speed, revealing significant correlations to peak wrist joint centre linear velocity (r = 0.767), acceleration phase duration (r = −0.543), shoulder internal/external rotation angle at shuttlecock contact (r = 0.508) and X-factor at the end of retraction (r = −0.484). Multiple linear regression analysis revealed 43.7% of the variance in shuttlecock speed could be explained by acceleration phase duration and X-factor at the end of retraction, where shorter acceleration phase durations and more negative X-factor at end of retraction caused greater shuttlecock speeds. These results suggest that motions of the proximal segments (shoulder and pelvis–thorax separation) are critical to developing greater distal linear velocities, which subsequently lead to greater post-impact shuttlecock speed.

Joint- and subject-specific strategies in male basketball players across a range of countermovement jump heights

The purpose of this study was to investigate subject- and joint-specific strategies used by male basketball players as they increase their countermovement jump (CMJ) height from sub-maximal to maximal efforts. Lower extremity joint kinematics and kinetics were recorded as 11 male, NCAA Division I basketball players performed 8-10 CMJ across effort levels of approximately 25%, 50%, 75% and 100%. Simple correlation models were used to investigate the associations between effort levels (i.e., CMJ height) and joint mechanics (i.e., negative (eccentric) and positive (concentric) mechanical work performed at the hip, knee, and ankle joints) for each individual player and the entire group. Group-analyses showed that increases in all joint mechanical variables were associated with increases in CMJ height. In contrast, single-subject analyses revealed that players used individualised strategies, and selectively scaled the magnitude of mechanical work at none (n = 2), one (n = 2), two (n = 5), or all three (n = 2) joints as they increased CMJ efforts. In addition, individual players also appeared to selectively scale different combinations of eccentric or concentric joint work as they increased CMJ height. These results highlight that male basketball players use joint-specific strategies to increase CMJ height when progressively increasing CMJ effort.

The influence of model parameters on model validation

The study examined the sensitivity of two musculoskeletal models to the parameters describing each model. Two different models were examined: a phenomenological model of human jumping with parameters based on live subject data, and the second a model of the First Dorsal Interosseous with parameters based on cadaveric measurements. Both models were sensitive to the model parameters, with the use of mean group data not producing model outputs reflective of either the performance of any group member or the mean group performance. These results highlight the value of subject specific model parameters, and the problems associated with model validation.

Foot orthoses alter lower limb biomechanics but not jump performance in basketball players with and without flat feet

Background

Flat-footed individuals are believed to have poorer jump performance compared to normal-arched individuals. Foot orthoses are commonly used to support the deformed foot arch, and improve normal foot function. However, it is unclear if foot orthoses use affects jump performance in athletes. Our study aims to investigate if foot type and/or foot orthosis influence countermovement jump (CMJ) and standing broad jump (SBJ) performance and lower limb biomechanics.

Methods

Twenty-six male basketball players were classified into normal-arched (n = 15) or flat-footed (n = 11) groups using the Chippaux-Smirak index, navicular drop test, and the resting calcaneal angle measurement. They performed jumps with and without prefabricated foot orthoses. We measured jump height and distance for CMJ and SBJ, respectively. Hip, knee and ankle joint angles, angular velocities, moments and powers during take-off were also measured.

Results

For CMJ, the flat-footed group exhibited less ankle plantarflexion (F_1,24 = 8.407, p = 0.008, η_p² = 0.259 large effect) and less hip joint power (F_1,24 = 7.416, p = 0.012, η_p² = 0.244 large effect) than the normal-arched group. Foot orthoses reduced ankle eversion in both groups (F_1,24 = 6.702, p = 0.016, η_p² = 0.218 large effect). For SBJ, the flat-footed group produced lower peak hip angular velocity (F_1,24 = 7.115, p = 0.013, η_p² = 0.229 large effect) and generated lower horizontal GRF (F_1,24 = 5.594, p = 0.026, η_p² = 0.189 large effect) than the normal-arched group. Wearing foot orthoses reduced ankle eversion (F_1,24 = 5.453, p = 0.028, η_p² = 0.185 large effect), peak horizontal GRF (F_1,24 = 13.672, p = 0.001, η_p² = 0.363 large effect) and frontal plane ankle moment (F_1,24 = 4.932, p = 0.036, η_p² = 0.170 large effect).

Conclusion

Foot type and the use of foot orthoses influence take-off biomechanics, but not actual CMJ and SBJ performances in basketball players. Compared to the normal-arched individuals, flat-footed athletes generated smaller propulsion GRF and lower hip flexion velocity and power, which suggests possible compensatory movement strategies to maximise jump performance. Future studies may investigate whether these altered biomechanics, taking into consideration their respective magnitude and effect sizes, may have implications on lower limb injuries. The use of foot orthoses resulted in biomechanical changes in both the normal-arched and flat-footed groups but does not enhance jumping performance.

Manifestations of Proprioception During Vertical Jumps to Specific Heights

Artur, S, Bogdan, P, Kawczyński, A, Winiarski, S, Grzegorz, J, and Andrzej, R. Manifestations of proprioception during vertical jumps to specific heights. J Strength Cond Res 31(6): 1694–1701, 2017—Jumping and proprioception are important abilities in many sports. The efficiency of the proprioceptive system is indirectly related to jumps performed at specified heights. Therefore, this study recorded the ability of young athletes who play team sports to jump to a specific height compared with their maximum ability. A total of 154 male (age: 14.8 ± 0.9 years, body height: 181.8 ± 8.9 cm, body weight: 69.8 ± 11.8 kg, training experience: 3.8 ± 1.7 years) and 151 female (age: 14.1 ± 0.8 years, body height: 170.5 ± 6.5 cm, body weight: 60.3 ± 9.4 kg, training experience: 3.7 ± 1.4 years) team games players were recruited for this study. Each participant performed 2 countermovement jumps with arm swing to 25, 50, 75, and 100% of the maximum height. Measurements were performed using a force plate. Jump height and its accuracy with respect to a specified height were calculated. The results revealed no significant differences in jump height and its accuracy to the specified heights between the groups (stratified by age, sex, and sport). Individuals with a higher jumping accuracy also exhibited greater maximum jump heights. Jumps to 25% of the maximum height were approximately 2 times higher than the target height. The decreased jump accuracy to a specific height when attempting to jump to lower heights should be reduced with training, particularly among athletes who play team sports. These findings provide useful information regarding the proprioceptive system for team sport coaches and may shape guidelines for training routines by working with submaximal loads.

Effects of two neuromuscular training programs on running biomechanics with load carriage: a study protocol for a randomised controlled trial

Background

In recent years, athletes have ventured into ultra-endurance and adventure racing events, which tests their ability to race, navigate, and survive. These events often require race participants to carry some form of load, to bear equipment for navigation and survival purposes. Previous studies have reported specific alterations in biomechanics when running with load which potentially influence running performance and injury risk. We hypothesize that a biomechanically informed neuromuscular training program would optimize running mechanics during load carriage to a greater extent than a generic strength training program.

Methods

This will be a two group, parallel randomized controlled trial design, with single assessor blinding. Thirty healthy runners will be recruited to participate in a six weeks neuromuscular training program. Participants will be randomized into either a generic training group, or a biomechanically informed training group. Primary outcomes include self-determined running velocity with a 20 % body weight load, jump power, hopping leg stiffness, knee extensor and triceps-surae strength. Secondary outcomes include running kinetics and kinematics. Assessments will occur at baseline and post-training.

Discussion

To our knowledge, no training programs are available that specifically targets a runner’s ability to carry load while running. This will provide sport scientists and coaches with a foundation to base their exercise prescription on.

Trial registration

ANZCTR (ACTRN12616000023459) (14 Jan 2016)

Electronic supplementary material

The online version of this article (doi:10.1186/s12891-016-1271-9) contains supplementary material, which is available to authorized users.