Bilateral comparison of propulsion mechanics during single-leg vertical jumping

Countermovement jump and vertical hop demonstrate braking/deceleration and performance alterations after ACL reconstruction with BMA, DBM, and suture tape augmentation

Objectives

This study evaluated countermovement jump and Single Leg Jump measures to identify landing measures that best distinguish a novel Anterior Cruciate Ligament reconstruction technique using bone marrow aspirate, demineralized bone matrix, and suture tape augmentation patients from controls. The secondary objective assessed performance differences between operated and non-operated limbs post-reconstruction. The hypothesis was that novel Anterior Cruciate Ligament reconstruction patients at return to sport would not differ from controls during landing and that the operated limb's performance would not differ from the unoperated limb.

Methods

The study included 31 patients with the novel reconstruction technique matched with controls in a 1:10 ratio based on age, sex, weight, and height. Both groups underwent screening and were compared during a Countermovement Jump. Using a Sparta Science Force Platform, each patient's unoperated and operated limbs were also compared for Single Leg Jump post-op (6.5 months).

Results

Test patients showed no difference in center of pressure during landing of both jumps compared to controls (P=0.27) and the uninvolved limb (P=0.26). Test patients exhibited increased braking impulse relative to the uninvolved limb during Single Leg Jump (P<0.001). Deceleration upon landing of Countermovement Jump was also increased compared to controls (P<0.001). Test patients demonstrated slower concentric time during a Countermovement Jump compared to controls (P=0.03) and significantly slower compared to the uninjured leg (P<0.001). Countermovement Jump height was decreased compared to controls (P<0.001). Single-leg jump height was decreased in the injured limb compared to the uninjured limb (P<0.001).

Conclusions

Test patients did not show significant differences in landing motion compared to controls or the uninvolved leg. However, power and performance alterations were evident at Return to Sport after reconstruction. Although these results are quite promising, they may be too preliminary to draw definitive conclusions. Double and single-legged assessments should be considered in return-to-sport decision-making.

Inter-limb differences in unilateral countermovement jump height are not associated with the inter-limb differences in bilateral countermovement jump force production

This study aimed to explore the relationship between the inter-limb differences in unilateral countermovement (CMJ) height and the inter-limb differences in bilateral CMJ force production, and to elucidate whether the self-reported preferred leg contributes more to force production than the non-preferred leg. Twenty-three senior basketball players performed in a single session eight unilateral CMJs (four with each leg) and four bilateral CMJs. Impulse, peak force, mean force were recorded during the bilateral CMJ, and jump height during the unilateral CMJ. Small correlations were observed between the inter-limb differences in unilateral CMJ height and the inter-limb asymmetries in bilateral CMJ impulse, peak force, and mean force (p ≥ 0.171; r≤-0.142). The self-reported preferred leg revealed a higher performance in 7 out of 23 participants (Kappa = -0.20) for the unilateral CMJ height, 7 out of 23 participants (Kappa = -0.11) for the bilateral CMJ impulse, 6 out of 23 participants (Kappa = -0.36) for the bilateral CMJ peak force, and 8 out of 23 participants (Kappa = -0.34) for the bilateral CMJ mean force. These results highlight that the asymmetries detected during bilateral CMJs cannot be extrapolated to unilateral CMJs, and that the preferred leg generally contributes less to force production than the non-preferred leg during both bilateral and unilateral CMJs.

Identification of potential risk factors for lower limb injuries in female team-sport athletes: a prospective cohort study

OBJECTIVES

The purpose of this prospective cohort study was to assess the associations between lower limb injuries in female team-sport athletes and a number of factors. The potential risk factors explored included (1) lower limb strength, (2) history of life-event stress, (3) family history of ACL injuries, (4) menstrual history, and (5) history of oral contraception use.

METHODS

One hundred and thirty-five female athletes aged between 14 and 31 years (mean: 18.8 ± 3.6 years) from rugby union (n = 47), soccer (n = 72), and netball (n = 16) volunteered to participate in this study. Demographics, history of life-event stress, injury history and baseline data were obtained prior to the competitive season. The following strength measures were collected: isometric hip adductor and abductor strength, eccentric knee flexor strength and single leg jumping kinetics. Athletes were then followed for 12 months, and all lower limb injuries sustained were recorded.

RESULTS

One hundred and nine athletes provided one-year follow-up injury data, of whom, 44 suffered at least one lower limb injury. All athletes who reported high scores for negative life-event stress sustained lower limb injuries. Non-contact lower limb injury was positively associated with weak hip adductor strength (OR: 0.88; 95%CI: 0.78-0.98; p = 0.017), and between-limb adductor (OR: 5.65; 95%CI: 1.61-19.7.; p = 0.007) and abductor (OR: 1.95; 95%CI: 1.03-3.71; p = 0.039) strength asymmetries.

CONCLUSION

History of life event stress, hip adductor strength, and between-limb adductor and abductor strength asymmetries offer potential novel avenues for investigating injury risk factors in female athletes.

Validity and reliability of the My Jump 2 app for detecting interlimb asymmetry in young female basketball players

Introduction

The aim of this study was to examine the validity and reliability of the My Jump 2 app for the assessment of interlimb jump asymmetry in young female basketball players.

Methods

Nine athletes (age 15 ± 0.9 years; weight 62.9 ± 5.8 kg; height 173.6 ± 6.1 cm) performed single-leg drop jumps (DJs) and both-leg drop jumps on a force plate (Kistler Quattro jump) and were simultaneously recorded on two smartphones using the My Jump 2 app. Jump height from flight time and contact time data were statistically analyzed to evaluate the validity of two different camera settings, drop jump performance, and interlimb jump asymmetry in basketball players. The testing was repeated after 1 week for test retest reliability.

Results

High test-retest reliability [intraclass correlation coefficient (ICC) > 0.88] was observed in DJ height. High correlation between the force plate and the My Jump 2 app was observed in DJ height (r = 0.99) and DJ contact time (r = 0.98). For the interlimb jump height asymmetries, mean differences were 0.6 percentages for the My Jump 2 app and the force plate, respectively (p = 0.77). Inter-device reliability revealed almost perfect correlation for the DJ height (ICC = 0.99, r = 0.98).

Conclusion

The My Jump 2 app is a valid and reliable tool to assess drop jump performance and interlimb asymmetry in young female basketball players.

Difference Asymmetry between Preferred Dominant and Non-Dominant Legs in Muscular Power and Balance among Sub-Elite Soccer Players in Qatar

The objective of this study was to determine and compare leg asymmetry between preferred dominant and non-dominant legs in muscular power and balance among sub-elite soccer (football) players in Qatar. Thirty-two professional local soccer players from the Qatar Stars League (Second Division) participated in the study (23.1 ± 6.1 years). They were classified according to their preferred dominant leg (preferred leg to kick the ball). Twenty-two players had a right dominant leg, and the remaining ten had a left dominant leg. Countermovement jump (CMJ) was used to measure unilateral and bilateral vertical jump performances. The Y-balance test (YBT) was used to assess dynamic balance. No significant differences were found between the dominant and non-dominant leg for CMJ flight height (p > 0.05; asymmetry index (AI) = 1.83 ± 11.46) or the relative and absolute reach distance derived from the YBT (p > 0.05; AI (relative) = −0.45 ± 9.68, AI (absolute) = −0.60 ± 12.3). Bilateral asymmetry in dynamic balance was not significant for any of the anterior, posteromedial, or the posterolateral reaching directions (p > 0.05). The selected football players demonstrated an acceptable level of leg symmetry for power and dynamic balance. These findings may prove helpful for the assessment and evaluation of talents and should help to develop and optimize training regimes.

Foot tracking can be an alternative to determine foot strike and take-off during vertical jumps

Determining foot strike and take-off during vertical jumps is essential to calculate a range of performance measures, which normally requires the use of expensive equipment such as force platforms. This study evaluated whether tracking the foot centre of mass(CoM) and hallux could be suitable alternatives to determine foot strike and take-off during jumps. Thirteen recreational runners performed six unilateral jumps. Foot strike and take-off instants were observed using three algorithms from foot CoM, pelvis CoM and the hallux marker and results were compared with data determined by the force platform. Bland-Altman method and Cohen effect sizes were used to assess the differences between methods. For foot strike, the difference between the foot CoM and the force platform (12 ms, d < 0.01) was smaller than using the pelvis CoM (46 ms, d < 0.01) and similar to the hallux (16 ms, d < 0.01). For the take-off, the foot CoM produced the smallest difference (i.e., 4 ms, d < 0.01; pelvis =  22 ms, d < 0.01 and hallux =  18 ms, d < 0.01). The foot CoM seems to yield the closest agreement with the force platform when determining foot strike and take-off during vertical jumps. However, the hallux marker can be used as an alternative to the foot CoM once corrected for mean bias.

The influence of limb role, direction of movement and limb dominance on movement strategies during block jump-landings in volleyball

The identification of movement strategies in situations that are as ecologically valid as possible is essential for the understanding of lower limb interactions. This study considered the kinetic and kinematic data for the hip, knee and ankle joints from 376 block jump-landings when moving in the dominant and non-dominant directions from fourteen senior national female volleyball players. Two Machine Learning methods were used to generate the models from the dataset, Random Forest and Artificial Neural Networks. In addition, decision trees were used to detect which variables were relevant to discern the limb movement strategies and to provide a meaningful prediction. The results showed statistically significant differences when comparing the movement strategies between limb role (accuracy > 88.0% and > 89.3%, respectively), and when moving in the different directions but performing the same role (accuracy > 92.3% and > 91.2%, respectively). This highlights the importance of considering limb dominance, limb role and direction of movement during block jump-landings in the identification of which biomechanical variables are the most influential in the movement strategies. Moreover, Machine Learning allows the exploration of how the joints of both limbs interact during sporting tasks, which could provide a greater understanding and identification of risky movements and preventative strategies. All these detailed and valuable descriptions could provide relevant information about how to improve the performance of the players and how to plan trainings in order to avoid an overload that could lead to risk of injury. This highlights that, there is a necessity to consider the learning models, in which the spike approach unilaterally is taught before the block approach (bilaterally). Therefore, we support the idea of teaching bilateral approach before learning the spike, in order to improve coordination and to avoid asymmetries between limbs.

Assessing Interlimb Jump Asymmetry in Young Soccer Players: The My Jump 2 App

BACKGROUND

Jumps are important evaluation tools for muscle strength and power and for interlimb asymmetries. Different jump tests are well related to athletic performance, prediction of injury risk, and common motor gestures of several sports such as soccer. Low-cost mobile applications (apps) have gained popularity for this measure. The authors hypothesized that the My Jump 2 app would be a valid tool to assess drop-jump performance and interlimb asymmetry in soccer players.

METHODS

Eleven male soccer players took part in this study (18.2 [1.3] y, 69.9 [9.5] kg, 174 [6.6] cm). The athletes performed each test twice on a force plate (gold-standard method), while the jumps were recorded through the mobile app. Measures with the My Jump 2 app were applied by 2 evaluators, independently and in duplicate (interrater and intrarater reliability). The agreement analysis between both evaluations was done using an intraclass correlation coefficient and Bland-Altman plots.

RESULTS

Compared with the force platform, the app tested showed excellent reliability for the drop jump's flight time and interlimb asymmetry (intraclass correlation coefficient > .98). For interlimb contact-time asymmetry, the values were 18.4 (9.9) and 19.1 (9.9) milliseconds for the My Jump 2 app and the force platform, respectively (P = .88). For flight-time asymmetries, the values were 389.7 (114.3) and 396.8 (112.5) milliseconds for the My Jump 2 app and the force platform, respectively (P = .88).

CONCLUSION

The My Jump 2 app is a valid tool to assess drop-jump and interlimb asymmetry in soccer players.

Relationship between Inter-Limb Asymmetries and Physical Performance in Rink Hockey Players

The magnitude of inter-limb asymmetries has been reported in several studies in different team sports but only some of them have analysed their effects on sports performance. The main purpose of this cross-sectional study was to determine inter-limb asymmetries and examine their relationship with different physical performance tests in rink hockey players. Nineteen rink hockey players (age: 23.37 ± 4.82 years; body height: 1.75 ± 0.06 cm; body mass: 73.16 ± 9.87 kg) performed a mid-season battery of fitness tests consisting of 30 m sprint, countermovement jump (CMJ), and half back squat. Inter-limb asymmetries were assessed using the single leg vertical countermovement jump test (SLCJ-V), single leg horizontal countermovement jump test (SLCJ-H), and 180° change of direction test (COD). Results show a significant relationship between asymmetry in the SLCJ-H test, 30 m sprint (r = 0.63, p < 0.01) and CMJ performances (r = −0.52, p < 0.05). Additionally, asymmetry in the SLCJ-V showed a significant relationship with CMJ performance (r = −0.46, p < 0.05). These findings suggest that training programs should aim to reduce the inter-limb asymmetries in rink hockey players to improve their performance. Practitioners and coaches can use this information to assess the potential impact of asymmetries on physical performance in rink hockey players.

Can kinematic and kinetic differences between planned and unplanned volleyball block jump-landings be associated with injury risk factors?

INTRODUCTION

Injury prevention programs for athletes are still limited by a lack of understanding of specific risk factors that can influence injuries within different sports. The majority of studies on volleyball have not considered the movement patterns when moving in different directions or in planned and unplanned block jump-landings.

METHODS

This study investigated all planes mechanics between the lead and trail limb when moving in dominant and non-dominant directions, for both planned and unplanned jump-landings in thirteen semi-professional female volleyball players. Ankle, knee and hip joint kinematics, kinetics and joint stiffness were recorded.

RESULTS

Our results showed statistically significant differences between the lead limb and the trail limb in the hip flexion angles, moments and velocity; in the knee flexion angles, moments, stiffness, power and energy absorption and in the ankle dorsiflexion, power and energy absorption, showing a tendency where the lead limb has a higher injury risk than the trail limb. When considering planned versus unplanned situations, there were statistically significant differences in knee flexion angles, moments, power and energy absorption; and hip contact angle, flexion angular velocity and energy absorption, with musculoskeletal adaptations in the planned situations.

DISCUSSION

It appears that the role of the limb, either lead or trail, is more important than the limb dominance when performing directional jump-landings, with the lead limb having a higher implication on possible overuse injuries than the trail limb. Furthermore, planned movements showed a difference in strategy indicating greater implications to possible overuse injuries than in the unplanned situations which may be associated with more conscious thought about the movements.

CONCLUSION

Coaches should consider unilateral coordination training in both landing directions for the lead and trail limb, and should adapt training to replicate the competition environment, using unplanned situations to minimize asymmetries to might reduce injury risks.

Heart Rate Variability, Neuromuscular and Perceptual Recovery Following Resistance Training

We quantified associations between changes in heart rate variability (HRV), neuromuscular and perceptual recovery following intense resistance training (RT). Adult males (n = 10) with >1 year RT experience performed six sets to failure with 90% of 10 repetition maximum in the squat, bench press, and pull-down. Changes (∆) from pre- to immediately (IP), 24 and 48 h post-RT were calculated for neuromuscular performance markers (counter-movement jump peak power and mean concentric bench press and squat velocity with load corresponding to 1.0 m∙s⁻¹) and perceived recovery and soreness scales. Post-waking natural logarithm of the root-mean square of successive differences (LnRMSSD) in supine and standing positions were recorded pre-RT (5 day baseline), IP and two mornings post-RT. All parameters worsened at IP (p < 0.05). LnRMSSD measures were not different from baseline by 24 h. Neuromuscular markers were not different from pre-RT by 48 h. Perceptual measures remained suppressed at 48 h. No significant associations among ∆ variables were observed (p = 0.052–0.978). These data show varying timeframes of recovery for HRV, neuromuscular and perceptual markers at the group and individual level. Thus, post-RT recovery testing should be specific and the status of one metric should not be used to infer that of another.

Countermovement Jump Inter-Limb Asymmetries in Collegiate Basketball Players

The purpose of the present study was to establish the intrasession and intersession reliability of variables obtained from a force plate that was used to quantitate lower extremity inter-limb asymmetry during the bilateral countermovement jump (CMJ). Secondarily, a comparison was performed to determine the influence of the jump protocol CMJ with or without an arm swing (CMJ AS and CMJ NAS, respectively) on inter-limb asymmetries. Twenty-two collegiate basketball players performed three CMJ AS and three CMJ NAS on dual force platforms during two separate testing sessions. A majority of variables met the acceptable criterion of intersession and intrasession relative reliability (ICC > 0.700), while fewer than half met standards established for absolute reliability (CV < 10%). CMJ protocol appeared to influence asymmetries; Concentric Impulse-100 ms, Eccentric Braking Rate of Force Development, Eccentric Deceleration, and Force at Zero velocity were significantly different between jumping conditions (CMJAS versus CMJ NAS; p < 0.05). The present data establish the reliability and smallest worthwhile change of inter-limb asymmetries during the CMJ, while also identifying the influence of CMJ protocol on inter-limb asymmetries, which can be useful to practitioners and clinicians in order to effectively monitor changes associated with performance, injury risk, and return-to-play strategies.

Lower Limb Neuromuscular Asymmetry in Volleyball and Basketball Players

The primary objective of the present study was to evaluate the agreement between the dominant leg (DL) (determined subjectively) and the stronger leg (SL) (determined via a functional test) in a group of basketball and volleyball players. The secondary objective was to calculate lower limb neuromuscular asymmetry when comparing the DL vs the non-dominant leg (NDL) and the SL vs the weaker (WL) leg in the whole group and when differentiating by sex. Seventy-nine male and female volleyball and basketball players (age: 23.7 ± 4.5 years) performed three single-leg vertical countermovement jumps (SLVCJ) on a contact mat. Vertical jump height and an inter-limb asymmetry index (ASI) were determined. Only 32 (40%) of the subjects had a concordance between the perception of their dominant leg and the limb reaching the highest jump height. Using the DL as the discriminating variable, significant (p<0.05) inter-limb differences were found in the total group of players. When comparing between sexes, significant differences (p<0.05) arose in the female group only. With regard to the WL vs. the SL, significant (p<0.05) differences were noted in the whole group and when stratified into males and females. The mean ASI ranged from 9.31% (males) to 12.84% (females) and from 10.49% (males) to 14.26% (females), when comparing the DL vs. the NDL and the SL vs. the WL, respectively. Subjective expression of leg dominance cannot be used as a predictor of limb jump performance. Vertical jump asymmetry of 10-15% exists and this can be considered as a reference value for male and female basketball and volleyball players.

Bilateral and unilateral vertical ground reaction forces and leg asymmetries in soccer players

The purposes of this study were to assess unilateral and bilateral vertical jump performance characteristics, and to compare the vertical ground reaction force characteristics of the impulse and landing phase of a vertical jump between the dominant and non-dominant leg in soccer players. The sample consisted of 20 male soccer players (22.80 ± 2.71 years, 1.88 ± 0.06 m, 76.47 ± 8.80 kg) who competed in the third division of the Spanish football league. Vertical jump performance was determined by testing the impulse and landing phase of a bilateral vertical jump, dominant leg vertical jump and non-dominant leg vertical jump. Significant differences (p < 0.05) between dominant and non-dominant legs were found in counter movement jump (CMJ) flight time (LA = -2.38%, d = 0.33), CMJ flight height (LA = -4.55%, d = 0.33) and CMJ speed take-off (LA = -2.91%, d = 0.42). No significant differences were found between the dominant and non-dominant leg in the F1 and F2 magnitudes during the landing phase, the time from the first contact of the foot with the ground to the production of F1, the time from the second contact of the foot with the ground to the production of F2, and the time to stabilization of the landing phase. Although differences were found between the dominant and non-dominant leg in the impulse phase of the jump, no significant differences were found between dominant and non-dominant legs in the landing phase of vertical jump variables.

Neuromuscular asymmetries in the lower limbs of elite female youth basketball players and the application of the skillful limb model of comparison

OBJECTIVES

Compare the ability of commonly used comparison models to detect neuromuscular asymmetries. A secondary purpose was to determine which neuromuscular task(s) has the greatest sensitivity to identify asymmetries based on the ASI (asymmetry index) calculation.

METHODS

Elite female youth basketball players (N = 29, age = 15.7 ± 1.34 y) performed the single leg countermovement jump in vertical, horizontal, and lateral directions, the star excursion balance test in the anterior, posteromedial, and posterolateral directions, and the sprint test with change of direction. Paired t-tests compared right and left limbs, the dominant (DL) and non-dominant (NDL) limbs, and the more/less skillful limbs.

RESULTS

The coincident identification between the more skillful leg and the leg subjectively described as the DL was low for all of the tasks performed (35%-52%). There were significant differences between the more and less skillful legs for all tasks, while performances between the right and left limbs and DL and NDL differed significantly for only one task each. The largest ASI detected in this study was found in the vertical single leg countermovement jump (14.11%).

CONCLUSIONS

The skillful limb model of comparison may be more useful than other models to detect neuromuscular asymmetries.

Comparison of ground reaction force asymmetry in one- and two-legged countermovement jumps

This study examined whether ground reaction force (GRF) asymmetry of 2-legged countermovement jumps (CMJ) is related to 1-legged CMJ asymmetry. The GRF asymmetry of a 2-legged CMJ has been suggested as a preferred test to the 1-legged CMJ for functional strength and power deficit assessment. Twenty-eight men and 30 women performed 5 trials each of a 1-legged CMJ with the right limband the left limb, and a 2-legged CMJ. Vertical GRFs were collected from each lower limb using 2 force platforms. Although several GRF variables were calculated, vertical impulse correlated most strongly with jump height in all conditions (p < 0.05), and they were used in subsequent analyses. A moderate correlation was found for impulse asymmetry between the 1- and 2-legged CMJs for women (r = 0.45, p < 0.05), but not for men (r = 0.06, p = 0.76). In contrast, cross-tabulation analyses of subjects presented with the same dominant characteristics in the 1- and 2-legged CMJs revealed poor associations for both men (Freeman-Halton exact p = 0.61) and women (Freeman-Halton exact p = 0.19). Only 11 women recorded the same dominant limb for both 1- and 2-legged CMJs. This suggests that impulse asymmetries found in the 1- and 2-legged CMJ were unrelated. As the 1-legged CMJ relies on the extension forces generated entirely from 1 limb, variations in jump heights and GRF impulses by left and right limbs separately were more indicative of functional strength differences between sides. Hence, it is recommended that the 1-legged CMJ is used when examining functional strength asymmetry in the lower limbs. In contrast, factors causing asymmetry in GRF impulses during 2-legged CMJs are more complicated and require further investigation.

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

Background:

The in-line lunge of the Functional Movement Screen (FMS) evaluates lateral stability, balance, and movement asymmetries. Athletes who score poorly on the in-line lunge should avoid activities requiring power or speed until scores are improved, yet relationships between the in-line lunge scores and other measures of balance, power, and speed are unknown.

Hypothesis:

(1) Lunge scores will correlate with center of pressure (COP), maximum jump height (MJH), and 36.6-meter sprint time and (2) there will be no differences between limbs on lunge scores, MJH, or COP.

Study Design:

Descriptive laboratory study.

Level of Evidence:

Level 3.

Methods:

Thirty-seven healthy, active participants completed the first 3 tasks of the FMS (eg, deep squat, hurdle step, in-line lunge), unilateral drop jumps, and 36.6-meter sprints. A 3-dimensional motion analysis system captured MJH. Force platforms measured COP excursion. A laser timing system measured 36.6-m sprint time. Statistical analyses were used to determine whether a relationship existed between lunge scores and COP, MJH, and 36.6-m speed (Spearman rho tests) and whether differences existed between limbs in lunge scores (Wilcoxon signed-rank test), MJH, and COP (paired t tests).

Results:

Lunge scores were not significantly correlated with COP, MJH, or 36.6-m sprint time. Lunge scores, COP excursion, and MJH were not statistically different between limbs.

Conclusion:

Performance on the FMS in-line lunge was not related to balance, power, or speed. Healthy participants were symmetrical in lunging measures and MJH.

Clinical Relevance:

Scores on the FMS in-line lunge should not be attributed to power, speed, or balance performance without further examination. However, assessing limb symmetry appears to be clinically relevant.

The assessment of function. Part II: clinical perspective of a javelin thrower with low back and groin pain

Assessment of an individual's functional ability can be complex. This assessment should also be individualized and adaptable to changes in functional status. In the first article of this series, we operationally defined function, discussed the construct of function, examined the evidence as it relates to assessment methods of various aspects of function, and explored the multi-dimensional nature of the concept of function. In this case report, we aim to demonstrate the utilization of a multi-dimensional assessment method (functional performance testing) as it relates to a high-level athlete presenting with pain in the low back and groin. It is our intent to demonstrate how the clinician should continually adapt their assessment dependent on the current functional abilities of the patients.

The effects of a prophylactic knee brace and two neoprene knee sleeves on the performance of healthy athletes: a crossover randomized controlled trial

Knee injury is one of the major problems in sports medicine, and the use of prophylactic knee braces is an attempt to reduce the occurrence and/or severity of injuries to the knee joint ligament(s) without inhibiting knee mobility. The aim of the present study was to examine the effect of one recently designed prophylactic knee brace and two neoprene knee sleeves upon performance of healthy athletes. Thirty-one healthy male athletes (age = 21.2 ± 1.5) volunteered as participants to examine the effect of prophylactic knee brace/sleeves on performance using isokinetic and functional tests. All subjects were tested in four conditions in a random order: 1. nonbraced (control) 2. using a neoprene knee sleeve 3. using a knee sleeve with four bilateral metal supports and 4. using a prophylactic knee brace. The study design was a crossover, randomized, controlled trial. Subjects completed single leg vertical jump, cross-over hop, and the isokinetic knee flexion and extension (at 60, 180, 300°/sec). Data were collected from the above tests and analyzed for jump height, cross-over hop distance, peak torque to body weight ratio and average power, respectively. Comparisons of these variables in the four testing conditions revealed no statistically significant difference (p>0.05). The selected prophylactic brace/sleeves did not significantly inhibit athletic performance which might verify that their structure and design have caused no complication in the normal function of the knee joint. Moreover, it could be speculated that, if the brace or the sleeves had any limiting effect, our young healthy athletic subjects were well able to generate a mean peak torque large enough to overcome this possible restriction. Further studies are suggested to investigate the long term effect of these prophylactic knee brace and sleeves as well as their possible effect on the adjacent joints to the knee.

Asymmetry in multi-directional jumping tasks

OBJECTIVES

Quantify and compare average symmetry indexes (ASI) across jumping directions (vertical, lateral and horizontal) and variables (jump distance and height, peak force and peak power) in a non-injured population of netball players.

METHODS

Nineteen sub-elite netball players (age: 19.5 ± 1.1 years, body mass: 75.1 ± 11.8 kg, height: 177.6 ± 5.2 cm) performed three single-leg countermovement jumps from a force plate in the vertical, horizontal and lateral directions. Force, power and jump height ASI's were calculated from force plate data. Jump distance ASI was calculated as the distance jumped.

RESULTS

Individual ASI's ranged from 0.0 to 48.6% while averaged ASI's ranged from 3.1% (peak force) to 11.4% (peak power). Significant (p ≤ 0.05) ASI differences were observed between vertical force (3.0%) and power (9.2%) (p = 0.02), horizontal power (11.4%) and jump distance (4.6%) (p < 0.001), horizontal force (8.0%) and distance (4.6%) (p < 0.001) and lateral power (10.0%) and jump distance (6.2%) (p = 0.05). The greatest ASI was found for the lateral direction (8.4 ± 1.2% averaged across the three variables).

CONCLUSIONS

There appears to be some variation in the magnitude of the ASI depending on the variable and direction used to quantify the asymmetry. Decisions need to be made by the strength and conditioning practitioner as to which variables and directions are specific to the requirements of their sport, position or activity.

Lower extremity strength and hopping and jumping ground reaction forces in children with neurofibromatosis type 1

The purpose of this study was to (1) extend the research findings of decreased muscular force production in grip strength to the lower extremity strength of children with NF1 and (2) to determine if there was a relationship between isometric strength and functional activities in children with NF1. Force production was assessed using a hand held dynamometer (HHD) and a functional task (hopping and jumping) on a force plate. Data from twenty-six children with NF1 were compared to data from 48 typically developing children of similar sex, weight and height. Children with NF1 demonstrated statistically significant lower force production with HHD (p<0.01) during hip extension, but similar force production for knee extension and ankle plantar flexion compared to the control group. A relationship existed between the ground reaction forces at take-off from both hopping and jumping and the force generated from knee extensor strength in the NF1 group. The addition of a functional task to hand held dynamometry is useful for determining a relationship between common clinical measures and functional activities.