Single-leg Countermovement Jumps Research Articles

The Effects of Complex Training on Neuromuscular Development of the Lower Limbs in Youth Netball Players

Objective: The high prevalence of injury in netball can be associated with intrinsic or extrinsic factors. Female athletes have an increased risk of injury as they enter into maturity due to increased joint laxity and a reduction in neuromuscular control, resulting in altered landing biomechanics and greater knee joint injury risk. This study sought to investigate whether complex training (CT) could improve neuromuscular strength and landing kinematics, thereby reducing injury risk to the knee. Methods: A within subject, repeated measures design was utilised. Ten youth netball academy players (age, 15.3 ± 0.9, years; height, 169.0 ± 7.0, cm; body mass, 62.2 ± 6.9, kg) participated and attended one familiarisation and two testing sessions (pre- and post-intervention). Participants’ were assessed on: countermovement jump (CMJ), landing error score system (LESS), and single leg countermovement jump (SLCMJ) of both limbs. All participants engaged in a 6 week, one day per week, strength training and plyometric intervention for the lower limbs utilising CT. Results: Significant improvements were evidenced for CMJ height (p = 0.001, d = 1.2 “moderate” effect), CMJ peak power output (PPO) (p = 0.001, d = 0.7 “small” effect), LESS (p = 0.002, d = 1.7 “large” effect), and SLCMJ left height (p = 0.01, d = 1.2 “moderate” effect) following the intervention. Conclusion: Performing one CT session a week over 6 weeks enhanced kinematics and performance of jumping activities both bilaterally and unilaterally, it also brought about reductions in asymmetries in young female athletes.

The Effects of Maturation on Measures of Asymmetry During Neuromuscular Control Tests in Elite Male Youth Soccer Players.

Asymmetry is a risk factor for male youth soccer players. There is a paucity of data confirming the presence of asymmetry using practically viable screening tasks in players at different stages of maturation. A cross-sectional sample (N = 347) of elite male youth soccer players who were either pre-, circa-, or post-peak height velocity (PHV) completed the following assessments: single-leg Y-Balance anterior reach, single-leg hop for distance, single-leg 75% hop and stick, and single-leg countermovement jumps. Single-leg countermovement jumps landing force asymmetry was higher in both circa- and post-PHV groups (P < .001; d = 0.41-0.43). Single-leg 75% hop and stick landing force asymmetries were also highest in circa-PHV players, but between-group comparisons were not statistically significant and effect sizes were small. Single-leg hop for distance and single-leg Y-Balance anterior reach asymmetries reduced with maturation; however, no group differences were significant, with small to trivial effect sizes (d ≤ 0.25). Stage of maturation did not have a profound effect on asymmetry. Between-limb differences in functional performance seem to be established in early childhood; thus, targeted interventions to reduce this injury risk factor should commence in pre-PHV athletes and be maintained throughout childhood and adolescence to ensure asymmetry does not increase.

Comparison Between Unilateral and Bilateral Plyometric Training on Single and Double Leg Jumping Performance

The phenomenon of bilateral deficit in jumping implies that greater muscle power can be developed when performing maximal single leg jumps, compared with two-leg jumps. Thus, it may be hypothesized that training with single leg plyometric exercises would be more effective compared to an equivalent volume of double leg plyometric training. PURPOSE: To compare the effects of unilateral and bilateral plyometric training on single and double leg jumping performance. METHODS: Fifteen moderately trained subjects (age: 19.6±2.1 yrs, height: 172±9 cm, body mass: 65.6±10.6 kg) were randomly assigned to either a unilateral (U, n=7) or a bilateral group (B, n=8). Both groups performed maximal effort plyometric leg exercises two times per week for 6 weeks (6 exercises per session, 3 sets of 10 repetitions per exercise), as well as 3 sets of knee extensions and flexions at 70%-90% of their 1 repetition maximum. The U group performed all plyometric and knee flexion/extension exercises with both legs, while the B group performed half the repetitions with each leg, so that the total exercise volume was the same. Jumping performance was assessed by double and single leg countermovement jumps (CMJ) and drop jumps (DJ) from 30 cm, measured using an optical measurement system (Optojump). Reactive strength index (RSI) was calculated from DJ data (jump height and ground contact time). Results were analyzed using a 2 x 2 ANOVA with repeated measures in one factor and Tukey’s post-hoc test. RESULTS: CMJ with both legs significantly improved equally in the U and B groups by 12.1±7.2% and 11.0±5.5% (p<0.001), respectively. However, single-leg CMJ, quantified as the sum of dominant and non-dominant single leg CMJ, only improved in the U group (19.0±7.1%, p<0.001) and was unchanged in the B group (3.4±8.4%, p=0.80). Similarly, RSI for single leg only improved in the U group (from 0.95±0.21 to 1.17±0.25 m·s-1, p=0.002), but not in the B group. CONCLUSIONS: Plyometric training with single leg exercises was more effective in increasing both single and double-leg jumping performance, compared to bilateral training.

Consistency of Field-Based Measures of Neuromuscular Control Using Force-Plate Diagnostics in Elite Male Youth Soccer Players.

Read, P, Oliver, JL, Croix, MD, Myer, GD, and Lloyd, RS. Consistency of field-based measures of neuromuscular control using force-plate diagnostics in elite male youth soccer players. J Strength Cond Res 30(12): 3304-3311, 2016-Deficits in neuromuscular control during movement patterns such as landing are suggested pathomechanics that underlie sport-related injury. A common mode of assessment is measurement of landing forces during jumping tasks; however, these measures have been used less frequently in male youth soccer players, and reliability data are sparse. The aim of this study was to examine the reliability of a field-based neuromuscular control screening battery using force-plate diagnostics in this cohort. Twenty-six pre-peak height velocity (PHV) and 25 post-PHV elite male youth soccer players completed a drop vertical jump (DVJ), single-leg 75% horizontal hop and stick (75%HOP), and single-leg countermovement jump (SLCMJ). Measures of peak landing vertical ground reaction force (pVGRF), time to stabilization, time to pVGRF, and pVGRF asymmetry were recorded. A test-retest design was used, and reliability statistics included change in mean, intraclass correlation coefficient, and coefficient of variation (CV). No significant differences in mean score were reported for any of the assessed variables between test sessions. In both groups, pVGRF and asymmetry during the 75%HOP and SLCMJ demonstrated largely acceptable reliability (CV ≤ 10%). Greater variability was evident in DVJ pVGRF and all other assessed variables, across the 3 protocols (CV range = 13.8-49.7%). Intraclass correlation coefficient values ranged from small to large and were generally higher in the post-PHV players. The results of this study suggest that pVGRF and asymmetry can be reliably assessed using a 75%HOP and SLCMJ in this cohort. These measures could be used to support a screening battery for elite male youth soccer players and for test-retest comparison.

Core stability training on lower limb balance strength

This study aimed to assess the effects of core stability training on lower limbs’ muscular asymmetries and imbalances in team sport. Twenty footballers were divided into two groups, either core stability or control group. Before each daily practice, core stability group (n = 10) performed a core stability training programme, while control group (n = 10) did a standard warm-up. The effects of the core stability training programme were assessed by performing isokinetic tests and single-leg countermovement jumps. Significant improvement was found for knee extensors peak torque at 3.14 rad · s−1 (14%; P < 0.05), knee flexors peak torque at 1.05 and 3.14 rad · s−1 (19% and 22% with P < 0.01 and P < 0.01, respectively) and peak torque flexors/extensors ratios at 1.05 and 3.14 rad · s−1 (7.7% and 8.5% with P < 0.05 and P < 0.05, respectively) only in the core stability group. The jump tests showed a significant reduction in the strength asymmetries in core stability group (−71.4%; P = 0.02) while a concurrent increase was seen in the control group (33.3%; P < 0.05). This study provides practical evidence in combining core exercises for optimal lower limbs strength balance development in young soccer players.

The relationship of training load to physical-capacity changes during international tours in high-performance junior tennis players.

Given the travel that punctuates junior tennis development, an understanding of the changes in fitness owing to touring and the association between training loads (TLs) and fitness on return is vital. The authors investigated physical-capacity changes from pretour to posttour, determining if those changes were related to the TL of athletes on tour. Thirty junior athletes completed fitness testing before and after 4-wk tours. Testing included double-leg countermovement jump (CMJ), dominant single-leg and nondominant single-leg CMJ, speed (5, 10, 20 m), modified 5-0-5 agility (left and right), 10 × 20-m repeated-sprint ability (RSA), and multistage fitness tests. Repeated-measures ANOVAs determined physical-capacity change, with effect-size analysis establishing the magnitude of change. To avoid regression toward the mean, a 1/3-split technique was implemented for comparative analysis (high to low TLs). Moderate effects (d=0.50-0.70) for reductions of up to 3.6% in 5-, 10-, and 20-m speeds were observed. However, all remaining changes were only of trivial to small magnitude (d<0.40). Closer analysis of the interaction between TL and physical capacities (1/3-split) revealed that subjects who completed the greatest amount of total and tennis TL returned with a greater decline in speed and aerobic capacities (d>0.80). Furthermore, it was observed that match load dictates on- and off-court TL, with an increase in matches won understandably stunting exposure to off-court TL. Specific training should be prescribed on tour to maintain speed characteristics over a 4-wk international tour. On-tour training schedules should be carefully monitored to maximize specific TL exposure after losses on tour.

Evaluating lower-limb asymmetry in acl-patients: assesment of jumping performance and mechanical muscle function

Introduction: The ratio between the operated and nonoperated leg is typically used to distinguish between normal or abnormal test scores in knee patients (1). Traditionally, the asymmetry ratios are investigated by use of functional tests (i.e. one-leg jump for distance). However, mechanistic outcomes such as kinematic/kinetic data and isolated muscle force/power output may provide further insight into the origin of between-limb asymmetry. The study aim was to investigate differences in asymmetry ratios of unilateral jumpperformance bymeans of kinetic and kinematic analysis andmechanicalmuscle function in ACL-patients and healthy controls. Patients/materials and methods: This case-control study was performed in 23 ACL-reconstructed men (mean age: 27.2 ± 7.5 years and BMI: 25.4 ± 3.2) 18-30 month post-surgery and 25 healthy matched controls (mean age: 27.2 ± 5.4 years and BMI: 24.1 ± 1.8). Patients and controls performed (i) bilateral maximal counter movement jumps (CMJ) with each leg positioned on a separate force plate and (ii) maximal single-leg CMJs. Kinematic data were synchronously recorded by a 6 cameraViconMX system. Subsequently, center of mass jump height (JH), unilateral knee joint range of motion (ROM), unilateral peak (Mpeak) and mean sagittal knee moment (Mmean) were analyzed for the concentric phase, (iii) one-leg maximal jump for distance was performed [1], and (iv)maximal unilateral isometric knee extensor and flexor strength (MVC)weremeasuredusing stabilizeddynamometry [2]. Asymmetry ratios were calculated as operated/non-operated leg for ACLpatients, and non-dominant/dominant leg for controls. Good-tomoderate test-retest reliability has been reported for all measured variables [3]. Differences in asymmetry ratios were evaluated by student’s t-tests using a 0.05 level of significance. Results: No differences in age or BMI were observed between groups. CMJ:Asymmetry ratios for knee jointROMdiffered (p<0.01) between patients and controls in both types of CMJ (96.1% vs. 102.6% and 87.0% vs. 99.9% in bilateral and single-leg CMJs, respectively). Jump for distance: Patients demonstrated greater (p<0.01) asymmetry for jump length (92.9% vs. 98.6%). MVC: Asymmetry in hamstring MVC was greater (p<0.001) for patients than controls (77.4% vs. 101.3%). Discussion & conclusions: ACL patients showed reduced function of the operated leg 18-30 month post ACL-reconstruction for knee ROM, singleleg jump for distance and hamstring MVC. The most prominent reduction was observed for maximal hamstring muscle strength. This finding has significant clinical implications since the hamstring muscles are important protagonists to the ACL [4,5], with reduced hamstring MVC thus representing a potential risk factor for secondary ACL-rupture.

Concurrent assessments of lower limb loading patterns, mechanical muscle strength and functional performance in ACL-patients — A cross-sectional study

BackgroundFull recovery in muscle strength and functional performance may not be achieved after ACL-injury. Aim: The aim of this study is to investigate loading patterns during jumping, muscle function and functional performance in ACL-reconstructed patients and to investigate the origin of between-limb asymmetry by means of a 3-dimensional movement analysis. Design is cross-sectional. Methods23 ACL-reconstructed men (27.2±7.5years, BMI: 25.4±3.2) 27±7month post-surgery and 25 matched controls (27.2±5.4years, BMI: 24.1±1.8) were included. Participants performed (i) bilateral and (ii) unilateral counter movement jumps (CMJ). A 3-D movement analysis was performed by a six-camera Vicon MX-system. Subsequently, jump height (JH), knee joint range of motion (ROM), peak and mean sagittal knee moments were analyzed (iii) one-leg maximal jump for distance was performed, and (iv) maximal unilateral isometric knee extensor and flexor strength (MVC) were measured using stabilized dynamometry. ResultsNo in-between group differences in age or BMI were observed. CMJ: Between-limb asymmetry ratios for ROM differed (p<0.01) between patients and controls in both types of CMJ (96.1% vs. 102.6% and 87.0% vs. 99.9% in bilateral and single-leg CMJs, respectively). Jump for distance: Patients demonstrated greater (p<0.01) asymmetry for jump length (92.9% vs. 98.6%). MVC: Asymmetry in hamstring MVC was greater (p<0.001) for patients than controls (77.4% vs. 101.3%). ConclusionsACL-patients showed reduced function of the operated leg ~2years post ACL-reconstruction, especially for hamstring MVC. Hamstrings are important protagonists to the ACL, thus representing a potential risk factor for secondary ACL-rupture and/or osteoarthritis.

Evaluating Plyometric Exercises Using Time to Stabilization

Plyometric exercises are frequently used in strength and conditioning and rehabilitation programs because the landing phase of these exercises requires dynamic stabilization. This study examined the differences in landing stability of a variety of plyometric exercises by assessing time to stabilization (TTS), its reliability, and sex differences therein. Forty-nine men and women performed a variety of plyometric exercises thought to represent a continuum of difficulty of dynamic stabilization during landing. Plyometric exercises included line hops, cone hops, squat jumps, tuck jumps, countermovement jumps, dumbbell countermovement jumps, and single leg countermovement jumps, each performed for 3 repetitions on a force platform. A 2-way mixed analysis of covariance with repeated measures for plyometric exercise type was used to evaluate the main effects for plyometric exercise type and the interaction between plyometric exercise type and sex for TTS. Subject jumping ability was evaluated as a covariate. Results revealed significant main effects for plyometric exercise type (p < or = 0.001) and for the interaction between plyometric exercise type and sex (p = 0.002). Bonferroni adjusted post hoc analysis demonstrated differences in TTS between a number of plyometric exercises for men and women. Reliability analysis revealed intraclass correlation coefficients ranging from 0.51 to 0.86 with no significant difference between trials (p > 0.05). Practitioners who use plyometrics to train dynamic stability should create programs that progress the intensity of the exercises based on the results of this study. This study also demonstrated that TTS is moderately to highly reliable for a variety of jumping conditions for both men and women.

Reliable lower limb musculoskeletal profiling using easily operated, portable equipment

Objectives Jumping performance and movement-based screening tests are commonly performed on athletes pre-season. Little is known regarding the test-retest reliability of performance tests and associated movement patterns using easily operated, portable and cost effective equipment. The purpose of this study was to establish the test-retest reliability of performance and video-derived movement characteristics of six screening tests measured simultaneously using a contact mat and two-dimensional video analysis. Methods Twenty-four subjects (17 male/7 female) were tested on three occasions 5–12 days apart to establish test-retest reliability of the measurement tools used. The tests used were anterior step-up, double and single-leg countermovement jumps, double and single-leg reactive (drop) jumps, and single-leg side springs. Results Measures of performance demonstrated less variability (mean-typical error expressed as a coefficient of variation, CV 2.8–4.3%) and higher reliability (intraclass correlation coefficients, ICC 0.98–0.99) for floor-based tests (preceding values) than drop tests (CV 10.3–13.2%, ICC 0.83–0.85). All video-derived movement characteristics demonstrated low variability (CV 3.2–4.8%), but lower rank order repeatability (ICC 0.43–0.79). Conclusion The findings suggest that screening tests performed from the floor and measured simultaneously using a contact mat and two-dimensional movement analysis are reliable, and trialling these tests for the pre-season screening of athletes is supported.

Gender and Bilateral Differences in Single-Leg Countermovement Jump Performance with Comparison to a Double-Leg Jump

Expectations may be for both legs to function identically during single- and double-leg vertical jumps. However, several reasons might prevent this from occurring. The goals of this investigation were twofold: assess the presence of side-to-side jump height differences during single-leg jumps in a homogenous group of healthy subjects and determine if those with a jump height asymmetry possessed consistent biomechanical differences during single-and double-leg jumps. Thirteen men and 12 women with competitive volleyball experience volunteered for the study. Significance was assessed at p < 0.05. The men jumped significantly higher than the women in all conditions and possessed differences in several anthropometric, kinematic, and kinetic parameters. Based on a three-jump average, all subjects had one leg that they could jump higher with (the dominant leg, DL). The men generated significantly greater maximum ground reaction forces and ankle joint powers on their DL whereas the women had no differences during the single-leg jumps. The only side-to-side differences that existed during the double-leg jumps were in the average ground reaction forces during propulsion. These findings suggest that equality of single-leg jump performance is the exception rather than the norm, with identification of consistent biomechanical attributes difficult within a group.

Effects of Muscle Damage on Stretch-Shortening Cycle Function and Muscle Stiffness Control

This experiment examined the effect of eccentric contraction-induced muscle damage on the stretch-shortening cycle and vertical leg spring stiffness during jumping activities. Ten moderately active male and female adult volunteers participated in this study (aged 23 +/- 2.3 years). Temporary muscle damage to the knee extensors was administered by a bout of eccentric contractions on an isokinetic dynamometer. Measurements were obtained of maximum voluntary force and of take-off velocities for single-leg countermovement jumps (CMJs), squat jumps (SJs), and drop jumps (DJs), performed on a specially constructed sledge and force plate apparatus. These measurements were obtained before and after the damage intervention, and the undamaged leg was used as a control. The results indicated that eccentric muscle damage significantly affected stretch-shortening cycle performance by causing relatively greater reductions in SJ performance than CMJ or DJ. The muscle damage intervention also significantly increased leg-spring stiffness, which indicates that the changes in leg stiffness may be an important adaptation resulting from eccentric exercise.