Relationship of jumping and agility performance in female volleyball athletes

Court sports often require more frequent changes of direction (COD) than field sports. Most court sports require 180 degrees turns over a small distance, so COD in such sports might be best evaluated with an agility test involving short sprints and sharp turns. The purposes of this study were to (a) quantify vertical and horizontal force during a COD task, (b) identify possible predictors of court-sport-specific agility performance, and (c) examine performance difference between National Collegiate Athletic Association Division I, II, and III athletes. Twenty-nine collegiate female volleyball players completed a novel agility test, countermovement (CM) and drop jump tests, and an isometric leg extensor test. The number of athletes by division was as follows: I (n = 9), II (n = 11), and III (n = 9). The agility test consisted of 4 5-meter sprints with 3 180 degrees turns, including 1 on a multiaxial force platform so that the kinetic properties of the COD could be identified. One-way analysis of variance revealed that Division I athletes had significantly greater countermovement jump heights than Division III, and the effect size comparisons (Cohen's d) showed large-magnitude differences between Division I and both Divisions II and III for jump height. No other differences in performance variables were noted between divisions, although effect sizes reached moderate values for some comparisons. Regression analysis revealed that CM displacement was a significant predictor of agility performance, explaining approximately 34% of the variance. Vertical force was found to account for much of the total force exerted during the contact phase of the COD task, suggesting that performance in the vertical domain may limit the COD task used herein. This study indicates that individuals with greater CM performance also have quicker agility times and suggests that training predominantly in the vertical domain may also yield improvements in certain types of agility performance. This may hold true even if such agility performance requires a horizontal component.     

Neuromuscular training improves performance and lower-extremity biomechanics in female athletes

The purpose of this study was to examine the effects of a comprehensive neuromuscular training program on measures of performance and lower-extremity movement biomechanics in female athletes. The hypothesis was that significant improvements in measures of performance would be demonstrated concomitant with improved biomechanical measures related to anterior cruciate ligament injury risk. Forty-one female basketball, soccer, and volleyball players (age, 15.3 +/- 0.9 years; weight, 64.8 +/- 9.96 kg; height, 171.2 +/- 7.21 cm) underwent 6 weeks of training that included 4 main components (plyometric and movement, core strengthening and balance, resistance training, and speed training). Twelve age-, height-, and weight-matched controls underwent the same testing protocol twice 6 weeks apart. Trained athletes demonstrated increased predicted 1 repetition maximum squat (92%) and bench press (20%). Right and left single-leg hop distance increased 10.39 cm and 8.53 cm, respectively, and vertical jump also increased from 39.9 +/- 0.9 cm to 43.2 +/- 1.1 cm with training. Speed in a 9.1-m sprint improved from 1.80 +/- 0.02 seconds to 1.73 +/- 0.01 seconds. Pre- and posttest 3-dimensional motion analysis demonstrated increased knee flexion-extension range of motion during the landing phase of a vertical jump (right, 71.9 +/- 1.4 degrees to 76.9 +/- 1.4 degrees ; left, 71.3 +/- 1.5 degrees to 77.3 +/- 1.4 degrees ). Training decreased knee valgus (28%) and varus (38%) torques. Control subjects did not demonstrate significant alterations during the 6-week interval. The results of this study support the hypothesis that the combination of multiple-injury prevention-training components into a comprehensive program improves measures of performance and movement biomechanics.     

Acute effects of verbal feedback on upper-body performance in elite athletes

Argus, CK, Gill, ND, Keogh, JWL, and Hopkins, WG. Acute effects of verbal feedback on upper-body performance in elite athletes. J Strength Cond Res 25(12): 3282-3287, 2011-Improved training quality has the potential to enhance training adaptations. Previous research suggests that receiving feedback improves single-effort maximal strength and power tasks, but whether quality of a training session with repeated efforts can be improved remains unclear. The purpose of this investigation was to determine the effects of verbal feedback on upper-body performance in a resistance training session consisting of multiple sets and repetitions in well-trained athletes. Nine elite rugby union athletes were assessed using the bench throw exercise on 4 separate occasions each separated by 7 days. Each athlete completed 2 sessions consisting of 3 sets of 4 repetitions of the bench throw with feedback provided after each repetition and 2 identical sessions where no feedback was provided after each repetition. When feedback was received, there was a small increase of 1.8% (90% confidence limits, ±2.7%) and 1.3% (±0.7%) in mean peak power and velocity when averaged over the 3 sets. When individual sets were compared, there was a tendency toward the improvements in mean peak power being greater in the second and third sets. These results indicate that providing verbal feedback produced acute improvements in upper-body power output of well-trained athletes. The benefits of feedback may be greatest in the latter sets of training and could improve training quality and result in greater long-term adaptation.     

Preferential quadriceps activation in female athletes with incremental increases in landing intensity

The purpose of this study was to identify alterations in preparatory muscle activation patterns across different drop heights in female athletes. Sixteen female high school volleyball players performed the drop vertical jump from three different drop heights. Surface electromyography of the quadriceps and hamstrings were collected during the movement trials. As the drop height increased, muscle activation of the quadriceps during preparatory phase also increased (p < .05). However, the hamstrings activation showed no similar increases relative to drop height. Female athletes appear to preferentially rely on increased quadriceps activation, without an increase in hamstrings activation, with increased plyometric intensity. The resultant decreased activation ratio of the hamstrings relative to quadriceps before landing may represent altered dynamic knee stability and may contribute to the increased risk of ACL injury in female athletes.     

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.     

Kinematic analysis of hip and knee angles during landing after imagery in female athletes

ABSTRACT: Sarafrazi, S, Bt Abdulah, RT, and Amiri-Khorasani, M. Kinematics analysis of hip and knee angles during landing after imagery in female athletes. J Strength Cond Res 26(9): 2356-2363, 2012-In sport settings, imagery is regarded as one of the most popular and effective techniques to enhance the learning strategies and performance of skills. However, its effect on the correction of improper technique such as landing, which causes injury, is not clear. Therefore, the purpose of this study is to investigate the effect of imagery on knee and hip flexion angle during jump landing in women. The landing motions were captured from 40 female physical education students (height: 166.05 ± 7.52 cm; mass: 55.75 ± 9.23 kg; age: 20.45 ± 1.66 years) using a 3-dimensional technique at 60 Hz by 3 video cameras. There was a significant difference between no imagery (27.04 ± 2.40°) and imagery (22.98 ± 1.95°) on knee valgus angle, and also, there was a significant difference between no imagery (44.88 ± 13.46°) and imagery (62.35 ± 8.34°) on the knee flexion angle (p ≤ 0.001). There is, in addition, a significant difference between the effect of no imagery (28.60 ± 4.88°) and imagery (39.73 ± 7.29°) on hip flexion angle (p ≤ 0.001). It seems that imagery can be used to correct motions and movements. Based on this finding, we concluded that imagery, probably, can be used as a training strategy to change athletic motion; however, the authors suggest further investigation into the efficacy of imagery in the prevention of anterior cruciate ligament injury.     

Timing of neuromuscular activation of the quadriceps and hamstrings prior to landing in high school male athletes, female athletes, and female non-athletes.

There is a discrepancy between males and females in regards to lower extremity injury rates, particularly at the knee [Agel, J., Arendt, E.A., Bershadsky, B., 2005. Anterior cruciate ligament injury in National Collegiate Athletic Association basketball and soccer: a 13-year review. American Journal of Sports Medicine 33, (4) 524-530]. Gender differences in neuromuscular recruitment characteristics of the muscles that stabilize the knee are often implicated as a factor in this discrepancy. There is considerable research in the area of gender differences in regards to neuromuscular characteristics of the lower extremity in response to perturbation; however, most studies have been performed on the adult population only. Additionally, there is no consensus as to the gender differences that have been demonstrated. The purpose of this study was to compare muscular preactivation of selected lower extremity muscles (vastus medialis, rectus femoris, and medial/lateral hamstrings) in adolescent female basketball athletes, male basketball athletes, and female non-athletes in response to a drop landing. Subjects in the female non-athlete group recruited rectus femoris significantly slower than both the female athlete and male athlete groups (619.9=588.5>200.1ms prior to ground contact). The female non-athlete group also demonstrated a significantly slower vastus medialis compared to the female athlete group (127.1 vs 408.1ms), but not significantly slower than the male athlete group (127.1 vs 275.7ms). There were no differences between female athletes and male athletes for time to initial contraction of any muscle groups. No differences were found among the groups for medial or lateral hamstring activation. This study demonstrates that physical conditioning due to basketball participation appears to affect neuromuscular recruitment in adolescents and reveals a necessity to find alternate methods of training the hamstrings for improved neuromuscular capabilities to prevent injury.     

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

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

Quadriceps and hamstrings prelanding myoelectric activity during landing from different heights among male and female athletes

ACL tear is a major concern among athletes, coaches and sports scientists. More than taking the athlete away from training and competition, ACL tear is a risk factor for early-onset of knee osteoarthritis, and, therefore addressing strategies to avoid such injury is pertinent not only for competitive athletes, but for all physically active subjects. Imbalances in the prelanding myoelectric activity of the hamstrings and quadriceps muscles have been linked to ACL injuries. We investigated the effect of landing from different heights on prelanding myoelectric activity of the hamstrings and quadriceps muscles in recreational athletes. Thirty recreational athletes (15 male and 15 female) performed three bilateral drop jumps from two different heights; 20 cm and 40 cm while myoelectric activity of the vastus medialis, rectus femoris, biceps femoris and medial hamstrings were collected. When increasing the height of drop landing tasks prelanding normalized myoelectric activity of the quadriceps was increased by 15–20% but no significant changes were found for the hamstrings. Female athletes exhibited higher activity of the medial hamstrings compared to their male counterparts. We concluded that increasing the height of drop landing tasks is associated with increased myoelectric activity of the quadriceps but not the hamstrings in recreational athletes. These differences in muscle activity may be related to increased risk for ACL injury when the height is increased. Female athletes demonstrated higher recruitment of the medial hamstrings.     

The drop-jump video screening test: retention of improvement in neuromuscular control in female volleyball players

A valgus lower limb alignment is commonly documented during noncontact anterior cruciate ligament injuries. We previously developed a videographic drop-jump test to measure overall lower limb alignment in the coronal plane as a screening tool to detect such an abnormal (valgus) position on landing. A neuromuscular retraining program developed for female athletes was shown to be effective in improving lower limb alignment on this test immediately after completion of training. What remained unknown was whether these improvements would be retained for longer periods of time. Therefore, this study was undertaken to determine if these improvements in overall lower limb alignment would be retained up to 1 year after the training. Sixteen competitive, experienced female high-school volleyball players underwent the video drop-jump test and then completed the neuromuscular retraining program. The program consisted of a dynamic warm-up, jump training, speed and agility drills, strength training, and static stretching and was performed 3 times a week for 6 weeks. The athletes repeated the drop-jump test immediately upon completion of training and then 3- and 12-months later. Significant improvements were found in the mean normalized knee separation distance between the pre and posttrained values for all test sessions (p < 0.01). Immediately after training, 11 athletes (69%) displayed significant improvements in the mean normalized knee separation distance that were retained 12 months later. Five athletes failed to improve. The video drop-jump test, although not a risk indicator for a knee ligament injury, provides a cost-effective general assessment of lower limb position and depicts athletes who have poor control on landing and acceleration into a vertical jump.     

Seasonal changes in jump performance and body composition in women volleyball players

The present study aimed to evaluate the effects of different resistance training programs on jump performance and body composition of female volleyball players of the highest Spanish division league over 24 weeks of training. Ten female volleyball players (27.41 ± 4.94 years; 72.2 ± 8.5 kg; 179.7 ± 6.4 cm) completed 24 weeks of training and testing using a linear periodization, progressing from general conditioning (weeks 1-4), to hypertrophy (weeks 5-8), then to maximum strength and power (weeks 9-16) and concluding with a specific strength training (weeks 17-24). Body composition was measured using bioelectrical-impedance analysis, and neuromuscular capacity was estimated by squat jump, countermovement jump, Abalakov jump, and 2 repetition maxima (2RM). After initial evaluation (PRE), the players were tested on 3 different occasions (POST: fourth week, POST 1: eighth week and POST 2: 24th week) of the training cycle. Muscle mass increased on (4.5%, p < 0.05) and fat-free mass (4.38%, p < 0.05), whereas fat percent decreased (13.90%, p < 0.05). All neuromuscular performance tests were increased from PRE to POST 2 (ranging from 17.64 to 20.89%, p < 0.01) and from POST 1 to POST 2 (ranging from 4.62 to 7.56% p < 0.01). The results suggest that the volleyball players studied continued improving power and strength capacity together with body composition during the course of the study. Finally, as major application, these data provide normative and performance standards for female volleyball players.     

Neuromuscular functioning of athletes and non-athletes in the drop jump

In many sports vertical jumping is important. This study compared neuromuscular functioning of the lower extremity muscles together with some kinetic and kinematic parameters before and during ground contact in drop jumps from two heights [0.4 m (DJ40) and 0.8 m (DJ80)] in 7 highly trained triple-jumpers and 11 physically active controls. The triple-jumpers jumped 32% higher in DJ40 and 34% higher in DJ80, had shorter braking and total contact times, and greater average and peak vertical ground reaction forces than the controls. In both drop jumps in the electromyogram pre-activity of the vastus lateralis and gastrocnemius muscles started earlier in the jumpers than in the controls. For the control group the increase in dropping height was associated with a decrease in the propulsion force, and resulted in more extended knee and ankle angles at touch down and more flexed angles at the deepest position than for the jumpers. All angular displacements for DJ80 were larger than for DJ40 in the control group. The triple jumpers and control subjects differed with respect to their neuromuscular functioning in the drop jump exercise and they responded in a different way to the increase in dropping height. Accepted: 2 April 1998     

Individuality and reproducibility in high-speed motion of volleyball spike jumps by phase-matching and averaging

For analysis of knee injuries in volleyball, we developed a system to obtain kinematic waveforms about the high-speed motion of volleyball spike jumps that could examine their individuality and reproducibility, with phase-matching and averaging. The form of six female players was recorded in two sessions of ten jumps each, with a video motion-analysis system, VICON, at the sampling frequency of 240 Hz. To identify individual jump characteristics despite differences from jump to jump, we averaged up to ten data sets with phases matched. For such matching, we defined and used a statistic, epsilon, as the arithmetic mean of all absolute differences in each of the angles at each time sampled, based on the least squares method. Statistical evaluation with adjusted coefficients of multiple determination and epsilon showed that intra-individual variation between the two sessions was significantly smaller than inter-individual variation; their means differed by more than 2 standard deviations (SD) and 3SD, respectively. Regression analysis showed that this system was reliable (p < 0.001). We concluded that the averaged data sets obtained by the system could embody the individuality of spike jumps, with satisfactory reproducibility.     

The effects of plyometric vs. dynamic stabilization and balance training on power, balance, and landing force in female athletes

Neuromuscular training protocols that include both plyometrics and dynamic balance exercises can significantly improve biomechanics and neuromuscular performance and reduce anterior cruciate ligament injury risk in female athletes. The purpose of this study was to compare the effects of plyometrics (PLYO) versus dynamic stabilization and balance training (BAL) on power, balance, strength, and landing force in female athletes. Either PLYO or BAL were included as a component of a dynamic neuromuscular training regimen that reduced measures related to ACL injury and increased measures of performance. Nineteen high school female athletes participated in training 3 times a week for 7 weeks. The PLYO (n = 8) group did not receive any dynamic balance exercises and the BAL (n = 11) group did not receive any maximum effort jumps during training. Pretraining vs. posttraining measures of impact force and standard deviation of center of pressure (COP) were recorded during a single leg hop and hold. Subjects were also tested for training effects in strength (isokinetic and isoinertial) and power (vertical jump). The percent change from pretest to posttest in vertical ground reaction force was significantly different between the BAL and PLYO groups on the dominant side (p < 0.05). Both groups decreased their standard deviation of center of pressure (COP) during hop landings in the medial/lateral direction on their dominant side, which equalized pretested side to side differences. Both groups increased hamstrings strength and vertical jump. The results of this study suggest that both PLYO and BAL training are effective at increasing measures of neuromuscular power and control. A combination of PLYO and BAL training may further maximize the effectiveness of preseason training for female athletes.     

Control of dynamic foot-ground interactions in male and female soccer athletes: Females exhibit reduced dexterity and higher limb stiffness during landing

Controlling dynamic interactions between the lower limb and ground is important for skilled locomotion and may influence injury risk in athletes. It is well known that female athletes sustain anterior cruciate ligament (ACL) tears at higher rates than male athletes, and exhibit lower extremity biomechanics thought to increase injury risk during sport maneuvers. The purpose of this study was to examine whether lower extremity dexterity (LED) – the ability to dynamically control endpoint force magnitude and direction as quantified by compressing an unstable spring with the lower limb at submaximal forces – is a potential contributing factor to the “at-risk” movement behavior exhibited by female athletes. We tested this hypothesis by comparing LED-test performance and single-limb drop jump biomechanics between 14 female and 14 male high school soccer players. We found that female athletes exhibited reduced LED-test performance (p=0.001) and higher limb stiffness during landing (p=0.008) calculated on average within 51 ms of foot contact. Females also exhibited higher coactivation at the ankle (p=0.001) and knee (p=0.02) before landing. No sex differences in sagittal plane joint angles and center of mass velocity at foot contact were observed. Collectively, our results raise the possibility that the higher leg stiffness observed in females during landing is an anticipatory behavior due in part to reduced lower extremity dexterity. The reduced lower extremity dexterity and compensatory stiffening strategy may contribute to the heightened risk of ACL injury in this population.     

The correlation of segment accelerations and impact forces with knee angle in jump landing

Impact forces and shock deceleration during jumping and running have been associated with various knee injury etiologies. This study investigates the influence of jump height and knee contact angle on peak ground reaction force and segment axial accelerations. Ground reaction force, segment axial acceleration, and knee angles were measured for 6 male subjects during vertical jumping. A simple spring-mass model is used to predict the landing stiffness at impact as a function of (1) jump height, (2) peak impact force, (3) peak tibial axial acceleration, (4) peak thigh axial acceleration, and (5) peak trunk axial acceleration. Using a nonlinear least square fit, a strong (r = 0.86) and significant (p < or = 0.05) correlation was found between knee contact angle and stiffness calculated using the peak impact force and jump height. The same model also showed that the correlation was strong (r = 0.81) and significant (p < or = 0.05) between knee contact angle and stiffness calculated from the peak trunk axial accelerations. The correlation was weaker for the peak thigh (r = 0.71) and tibial (r = 0.45) axial accelerations. Using the peak force but neglecting jump height in the model, produces significantly worse correlation (r = 0.58). It was concluded that knee contact angle significantly influences both peak ground reaction forces and segment accelerations. However, owing to the nonlinear relationship, peak forces and segment accelerations change more rapidly at smaller knee flexion angles (i.e., close to full extension) than at greater knee flexion angles.     

The relationship of body segment length and vertical jump displacement in recreational athletes

The purpose of this study was to determine if segmental skeletal length contributes to vertical jump (VJ) displacement in recreational athletes. Skeletal length measurements of the trunk, femur, tibia, and foot were obtained by palpation of bony landmarks and a standard tape measure. A pilot study (n = 10) examined the intratester and intertester reliability for each skeletal measure. The pilot investigation revealed fair to excellent intratester and intertester reliability. Seventy-eight recreational athletes (55 men and 23 women) with a mean age of 21.9 +/- 2.9 years participated in the investigation. Multiple regression analysis with gender as a categorical indicator variable revealed a significant gender difference; therefore, men and women were analyzed separately. Regression analysis for men identified foot length (p < 0.033, R(2) = 0.08) as the only significant skeletal length predictor of VJ displacement. None of the skeletal length measures was predictive of VJ displacement in women. Based on the results of this investigation, intrinsic skeletal length is not a strong predictor of VJ displacement in young adult recreational athletes.