Strength, Jumping and Change of Direction Speed Asymmetries in Soccer, Basketball and Tennis Players

The Effects of Workload Difference Between Limbs in Plyometric and Strength Exercises in Reducing Asymmetry in Change of Direction Ability During Basketball Season

ABSTRACT

Ujaković, F, and Šarabon, N. The effects of workload difference between limbs in plyometric and strength exercises in reducing asymmetry in change of direction ability during basketball season. J Strength Cond Res 37(11): 2282-2288, 2023-The topic of interlimb asymmetries has recently been extensively investigated; despite that, intervention for purpose of reducing them have been narrowly examined. The present study investigated the effects of maximal strength and plyometric resistance training program with 3:1 workload ratio (nondominant to dominant side) on change of direction deficit (CoDdef) asymmetry during the basketball season. Thirty-six highly trained male basketball players (19.3 ± 4.9 years) from different age categories (U-17, U-19, and senior) were divided into 2 groups: the control group ( n = 18) and the intervention group ( n = 18). The intervention group performed once-a-week training that consisted of strength (Bulgarian split squats) and jumping (single-leg countermovement jumps [SLCMJs]) part in which nondominant-to-dominant workload ratio was 3:1 during the 8-week period. Preintervention and postintervention testing included single-leg isometric squat, SLCMJ, 10-m sprint, and 505 test. Analysis of covariance results showed a statistically significant difference with large effect size ( p < 0.05; η2 = 0.26) when preintervention asymmetry was included as covariate. Post hoc analysis showed a statistically significant decrease in mean CoDdef asymmetry between preintervention (11.88%) and postintervention (4.47%) testing ( p < 0.01, effect size [ES] = -1.37). Isometric squat strength increased on nondominant side in the intervention group ( p < 0.05; ES = 0.77). No other performance or asymmetry variable showed significant change. In conclusion, a 3:1 workload of nonspecific movement task in favor of nondominant limb is an effective training strategy to reduce CoDdef asymmetry during basketball season.

Change-of-Direction Speed Assessments and Testing Procedures in Tennis: A Systematic Review

ABSTRACT

Schneider, C, Rothschild, J, and Uthoff, A. Change-of-direction speed assessments and testing procedures in tennis: a systematic review. J Strength Cond Res 37(9): 1888-1895, 2023-Change-of-direction speed (CODS) plays an essential role in tennis match play, and CODS performance is, therefore, commonly assessed and monitored in tennis players. Thus, the aim of this systematic review was to describe test characteristics, performance metrics, test-retest reliability, construct validity, and test outcomes of tests that are used to assess CODS in tennis players. A literature search conducted on PubMed and SPORTDiscus yielded 563 results. After applying the eligibility criteria, a total of 27 studies were included in the present review. Ten unique CODS tests were identified. 505 test variations were most frequently used across all studies, and total time required to complete the test was the predominant performance metric investigated. Intrasession test-retest reliability ranged from "moderate" to "excellent." Intersession test-retest reliability as well as the effects of tennis performance, sex, and age on CODS performance were unclear given the subject demographics and the limited number of studies that investigated these aspects. In conclusion, most studies included CODS tests that exhibit longer COD entry and total distances but similar COD angles to those seen during tennis match play. All CODS tests have at least "moderate" intrasession test-retest reliability. However, to improve CODS assessment methods and to increase our current understanding of CODS performance in tennis players, there is a need to conduct more research on the intersession test-retest reliability, construct validity, and the effects of sex, age, and tennis performance and to investigate other performance metrics that might provide additional insights into CODS (e.g., phase-specific performance variables).

Pivot Step Jump: A New Test for Evaluating Jumping Ability in Young Basketball Players

Jumping ability in basketball is usually assessed using standardized vertical jump tests. However, they lack specificity and do not consider the player’s basketball skills. Several studies have suggested performing specific jump tests, which are tailored to the movement patterns and requirements of a basketball game. The pivot step jump test (PSJT) is a novel test designed to evaluate the specific jumping abilities of basketball players by combining a pivot step on one leg with a maximum bilateral vertical jump. This study had two aims: to determine the reliability and validity of the PSJT using typical jump tests as the criterion measure and to demonstrate the PSJT as a practical test to evaluate specific jumping ability in young male and female basketball players. Twenty female (EGA; 14.0 ± 0.7 years, 59.3 ± 7.9 kg, 162.1 ± 5.5 cm) and fifteen male (EGB; 14.0 ± 0.7 years, 58.1 ± 7.7 kg, 170.3 ± 6.4 cm) basketball players participated in the study. The test−retest reliability of the PSJT within sessions (intrasession reliability) and across sessions (intersession reliability) was assessed within EGA. For the evaluation of validity, EGB performed the PSJT and a series of criterion jumping tests. For EGA, no changes (p > 0.05) were found in PSJT performance between test sessions and excellent intra- and intersession reliability was observed (ICCs > 0.75). Correlation coefficients indicated high factorial validity between the jumping tests and PSJT (r = 0.71−0.91, p < 0.001). The PSJT appears to offer a valid assessment of jumping ability in basketball and is a practical test for assessing sport-specific jumping skills in young basketball players.

Shoulder Torque Production and Muscular Balance after Long and Short Tennis Points

Tennis is an asymmetric sport characterized by a systematic repetition of specific movements that may cause disturbances in muscular strength, power, and torque. Thus, we assessed (i) the torque, power, ratio production, and bilateral asymmetries in the shoulder's external and internal rotations at 90 and 180°/s angular velocities, and (ii) the point duration influence of the above-mentioned variables. Twenty competitive tennis players performed external and internal shoulder rotations; an isokinetic evaluation was conducted of the dominant and non-dominant upper limbs before and after five and ten forehands. A higher torque production in the shoulder's internal rotations at 90 and 180°/s was observed for the dominant vs. non-dominant sides (e.g., 63.1 ± 15.6 vs. 45.9 ± 9.8% and 62.5 ± 17.3 vs. 44.0 ± 12.6% of peak torque/body mass, p < 0.05). The peak torque decreased only after ten forehands (38.3 ± 15.8 vs. 38.2 ± 15.8 and 39.3 ± 16.1 vs. 38.1 ± 15.6 Nm, respectively, p < 0.05), but without impacting speed or accuracy. Unilateral systematic actions of tennis players caused contralateral asymmetries, evidencing the importance of implementing compensatory training. The forehand kinematic assessment suggests that racket and wrist amplitude, as well as speed, are important success determinants in tennis.

Anterior-Posterior and Inter-Limb Lower Body Strength Asymmetry in Soccer, Basketball, Futsal, and Volleyball Players

Background and Objectives: The purpose of this study was twofold: (1) to examine strength asymmetries in elite athletes of different sports and (2) to examine the magnitude of asymmetries between elite and u18 athletes. Materials and Methods: A total of 254 athletes participated in this study. For the first purpose of the study, the group consisted of adult professional male basketball players (n = 30), elite male (n = 30) and female soccer players (n = 20), male futsal players (n = 30), elite male goalkeepers (n = 22), and professional female volleyball players (n = 20). For the second purpose, male youth goalkeepers (n = 22), youth female (n = 20) and male soccer players (n = 30), and youth male basketball players (n = 30) were compared to the adult athletes of the same sport. Asymmetries were measured utilizing a Humac Norm and Rehabilitation device. Testing included three maximal concentric flexion and extension repetitions at an angular speed of 60°/s. The differences in asymmetries were assessed using ANOVA followed by an LS means post-hoc analysis. An independent samples t-test was used to identify the differences between adult and youth players. Results: It was indicated that none of the groups demonstrated asymmetries greater than 10%, other than the elite female soccer players and female volleyball players. Significant differences were demonstrated between youth and adult soccer players (males and females), with the adult groups demonstrating increased asymmetries. Conclusions: Special consideration should be given to female soccer players and volleyball players, as soccer and volleyball practice and competition at the professional level may induce greater lower -limb asymmetries. The isokinetic parameters can be useful for planning strength and conditioning interventions in order to reduce or prevent those imbalances. Additional unilateral and bilateral jumping testing is encouraged for the verification of imbalances.

Associations between lower limb eccentric muscle capability and change of direction speed in basketball and tennis players

Background

The ability to perform a quick and rapid change of direction (CoD) is an important determinant of success in a variety of sports. Previous studies have already highlighted that eccentric strength is a dominant predictor of CoD. However, these studies evaluated eccentric strength through a limited number of outcome measures and used small sample sizes.

Methods

A total of 196 athletes participated in the study. The aim of our study was to investigate: (1) the correlation between eccentric outcome measures derived from different tests (Nordic hamstring exercise (NHE), countermovement jump (CMJ) and flywheel (FW) squats), (2) the association between eccentric outcome measures and CoD 90°, CoD 180°; and (3) proportion of explained variance in CoD performance.

Results

Very large associations (r = 0.783, p < 0.001) were observed between peak torque during NHE (NHE_PT) and force impulse during the eccentric phase of CMJ (CMJ_FI). Small to moderate correlations were calculated between peak eccentric force in flywheel squats and peak eccentric force in CMJ (r = 0.220-035, p < 0002). All eccentric CMJ outcome measures and NHE_PT were reported as moderate negative associations with both CoD tests. Eccentric measures explained 25.1% of the variance in CoD 90° (CMJ_PF, NHE_PT, F_0.125 -peak eccentric force during FW squats with 0.125 kg m² load), while the same outcome measures explained 37.4% of the variance for CoD 180°.

Conclusion

Our results suggest that different measures of eccentric strength specifically contribute to CoD performance. Therefore, for successful CoD performance, different aspects of eccentric strength training should be considered in testing and training (maximal eccentric strength, eccentric-concentric actions with fast execution).

Maximal vs. explosive knee extensor strength in professional soccer players: inter-limb asymmetries and relationship with knee function

AbstractThe main aims of this study were to compare the magnitude of inter-limb asymmetry (ILA) and the relation with self-reported knee function between maximal and explosive knee extensor strength outcomes in professional soccer players. Forty-six male soccer players completed different maximal isokinetic and isometric contractions of the knee extensors for the assessment of maximal strength (peak torque and maximal voluntary contraction (MVC) torque) and explosive strength (early, intermediate, late, and peak rate of torque development (RTD)). Self-reported knee function was assessed with the International Knee Documentation Committee (IKDC) and Lysholm knee scoring scales. Peak torque and MVC torque showed comparable ILAs (8-9%), both being significantly lower than all RTD ILAs (16% on average; p < 0.001). ILAs for early RTD (21%) and peak RTD (19%) were significantly higher than all the other variables (p < 0.05). Only early and intermediate RTD were significantly correlated - though weakly - with both IKDC (rho = 0.32 for both) and Lysholm (rho = 0.36 and 0.30, respectively) scores. We conclude that explosive knee extensor strength - early RTD in particular - exhibited larger ILAs and better relations with self-reported knee function than peak torque and MVC torque in professional soccer players. These results confirm the validity and functional relevance of early RTD and the need for its inclusion in routine performance testing for soccer players.

Influence of Strength Programs on the Injury Rate and Team Performance of a Professional Basketball Team: A Six-Season Follow-Up Study

This study aims to determine possible associations between strength parameters, injury rates, and performance outcomes over six seasons in professional basketball settings. Thirty-six male professional basketball players [mean ± standard deviation (SD): age, 30.5 ± 4.7 years; height, 199.5 ± 9.5 cm; body mass, 97.9 ± 12.9 kg; BMI 24.6 ± 2.5 kg/m2] participated in this retrospective observational study, conducted from the 2008-09 to the 2013-14 season. According to their epidemiological records, each player followed an individual plan designed within different strength training programs: Functional (n = 16), Eccentric (n = 8), or Resistance (n = 12). Seven hundred and fourteen valid records were obtained from 170 individual strength tests during 31 sessions. Tests performed were leg press, squat, and jerk. Parameters recorded were force, power, velocity, peak velocity, and time to peak velocity for strength; time loss injury and muscle injury for injury rate; and games won, games lost, and championships for performance outcomes. All the strength variables and injuries are independent of the strength programs (p < 0.01). The correlation analysis showed very significant relationships between muscular injuries and time to peak velocity (r = 0.94; p < 0.01), significant relationships between force and games lost (r = 0.85; p < 0.05), and muscular injuries with games lost (r = -0.81; p < 0.05) per season. Mean values per season described a possible association of force, time to peak velocity, and muscular injuries with performance outcomes (R 2 = 0.96; p < 0.05). In this specific context, strength variables and injury rate data show no association with a single type of strength training program in this cohort of high-performance basketball players.

Lower Extremity Flexibility Profile in Basketball Players: Gender Differences and Injury Risk Identification

Analysis of the flexibility profile of basketball players (BPs) can reveal differences in range of motion (ROM) by gender and also identify those players who are at higher risk for sports injuries. A descriptive observational study was conducted to determine the lower extremity flexibility profile of sixty-four basketball players and gender differences to identify players at higher risk of injury due to limited and asymmetric ROM in one or more movements. Participants: Sixty-four (33 male and 31 female) competitive athletes from the national leagues of the Spanish basketball league system participated in the present study (power of sample size ≥0.99). The eight passive ROM tests of the hip, knee and ankle were assessed using the ROM-SPORT battery. Each player completed a questionnaire on age, basic anthropometric data, dominant extremities, and training and sport-related variables. The lower extremity flexibility profile was established at 15° and 10° hip extension (HE), 39° and 38° ankle dorsiflexion with knee extended (ADF-KE), 40° and 39° ankle dorsiflexion with knee flexed (ADF-KF), 43° and 43° hip abduction (HAB), 75° and 61° hip abduction with the hip flexed (HAB-HF), 78° and 83° hip flexion with the knee extended (HF-KE), 134° and 120° knee flexion (KF), and 145° and 144° hip flexion (HF) by male and female basketball players, respectively. Sex differences in HE, HAB-HF, and KF were observed in BPs (p ≤ 0.01; Hedges’ g ≥ 1.04). Players reported limited ROM in ADF-KF, HE, HAB-HF, HF-KE, and KF; and asymmetric ROM mainly in HE, ADF-KE, KF, ADF-KF, and HF-KE. In conclusion, this study provides gender-specific lower extremity flexibility profile scores in BPs that can help athletic trainers and athletic and conditioning trainers to identify those players who are at higher risk of injury due to abnormal ROM scores.

Investigation of Inter-Limb Symmetry in Knee Extensors Using Different Strength Outcome Measures

Muscle performance between contra-lateral knee extensors is most often assessed using maximal test for isometric/isokinetic torque evaluation. Recently, the rate of force development scaling factor (RFD-SF) has been used to evaluate neuromuscular capacity with a range of submaximal target peak torques, which could highlight other aspects of inter-limb (a)symmetry. The aim of our study was to investigate the differences, associations, and agreement between inter-limb symmetries of knee extensors using maximal torque (T_max) rate of torque development (RTD), slope of the RFD-SF regression line (k), and theoretical peak of RTD (TP_RTD). A total of 236 young, healthy athletes participated in the cross-sectional study. All participants performed unilateral knee extension (maximal voluntary contraction protocol and RFD-SF protocol) with both legs in the isometric knee dynamometer. Inter-limb symmetries were calculated for each outcome measure. Our results showed significant differences between all symmetry values (T_max (91.7%), RTD (85.2%), k (94.2%), TP_RTD (95.9%)). Significant strong correlations were found between symmetry values calculated from k and TP_RTD (r = 0.88, p < 0.001), while weak correlation was found between T_max and RTD (r = 0.17, p < 0.01. Fair agreement regarding leg dominance was found between T_max and RTD values. Our results suggest that inter-limb (a)symmetries are metric- and task-specific.

Should We Use Unilateral or Bilateral Tasks to Assess Maximal and Explosive Knee Extensor Strength in Patients with Knee Osteoarthritis? A Cross-Sectional Study

Deficits in maximal and explosive knee extensor strength, which are usually assessed with unilateral tasks, are substantial in patients with knee osteoarthritis (KOA). The aim of this study was to investigate the clinical relevance of unilateral vs. bilateral tasks for assessing knee extensor strength in patients with KOA. This was achieved primarily by comparing unilateral and bilateral inter-limb strength asymmetries and secondarily by examining the relationship between unilaterally and bilaterally measured strength, and performance-based and self-reported function. Twenty-four patients with unilateral KOA (mean age: 65 ± 7 years) performed isometric gradual and explosive maximal voluntary contractions to assess, respectively their maximal and explosive strength. Performance-based and self-reported function were also evaluated with standard functional tests and questionnaires, respectively. Inter-limb asymmetries of maximal and explosive strength did not differ significantly between unilateral (mean asymmetry: 26 ± 15%) and bilateral tasks (22 ± 21%). In the same way, the relationships between knee extensor strength-measured either unilaterally or bilaterally-and performance-based or self-reported function were not influenced by the type of task. In conclusion, it does not seem to make a difference in terms of clinical relevance whether maximal and explosive knee extensor strength are evaluated with unilateral or bilateral tasks in KOA patients.

The Effect of Fatigue on Single-Leg Postural Sway and Its Transient Characteristics in Healthy Young Adults

Neuromuscular fatigue is known to impair balance ability, which is reflected in increased postural sway during quiet standing tasks. Recently, quantifying transient characteristics of postural sway has been suggested as an approach to obtain additional information regarding postural control. However, this approach is currently vastly unexplored. The purpose of this study was to investigate the effects of fatigue (induced by a repeated change of direction task) on postural sway and its transient characteristics during single-leg standing, including whole-trial estimates and indexes of transient behavior in young healthy active adults. The study involved 28 physically active students (14 females). Single-leg postural sway was recorded for 30s before and after a fatiguing protocol, which consisted of a repeated change of direction tasks. We calculated the traditional whole-trial estimates of postural sway [center-of-pressure (CoP) velocity and amplitude in anterior-posterior (AP) and medial-lateral (ML) directions] and corresponding transient behavior indexes, based on three 10-s intervals. Statistically significant sex×fatigue interaction with medium effect sizes was found for whole-trial CoP velocity in AP (p=0.028; η²=0.17) and ML directions (p=0.019; η²=0.19). Post-hoc test showed that both variables substantially decreased in female participants (p=0.041–0.045; d=0.54–0.56), but remained similar in males (p=0.194–0.294). There were small to medium statistically significant main effects of fatigue on transient index for CoP amplitude in both directions (p=0.042–0.049; η²=0.02–0.14). Notably, CoP AP amplitude increased in the first 10-s interval for males (before fatigue: 5.6±1.3mm; after fatigue: 6.3±1.6mm), while the CoP AP amplitude in the third interval remained similar after fatigue (before fatigue: 5.5±1.4mm; after fatigue: 5.1±1.2mm). In conclusion, the responses to fatigue in terms of postural sway were time interval specific, and there were certain sex-differences in responses to fatigue, which could be related to better ability to adapt balance strategies in females. Moreover, our results demonstrate that the indexes of transient behavior could perhaps detect smaller fatigue-induced changes in postural sway that are seen in whole-trial estimates.

Bilateral Symmetry of Jumping and Agility in Professional Basketball Players: Differentiating Performance Levels and Playing Positions

Although functional asymmetry is very common and normal in professional athletes, the better interlimb symmetry between dominant and nondominant sides (bilateral symmetry) could contribute to successful performance in basketball. The aim of this study was to evaluate the importance of bilateral symmetry of the one-leg jumping and agility performances in differentiating basketball players according to their (i) playing position (guards, forwards, and centers) and (ii) performance levels (first division vs. second division). The participants were 102 professional male basketball players, with all members of the teams competing in the two highest national divisions at the moment of testing (height: 194.92 ± 8.09 cm; body mass: 89.33 ± 10.91 kg; 21.58 ± 3.92 years of age). Performance levels (first division, N = 58 vs. second division, N = 44) and playing positions (guards, N = 48; forwards, N = 22; centers, N = 32) were observed as dependent variables. We measured one-leg jumping capacities (running vertical jump and lay-up vertical jump), basketball-specific preplanned agility (CODS), and basketball-specific reactive agility (RAG), all executed on dominant and nondominant sides. Accordingly, the bilateral symmetry of jumping and agility was calculated by calculating the ratio of the corresponding performances on the dominant and nondominant sides. Factorial analysis of variance (performance levels × positions) indicated that the bilateral symmetry of one-leg jumping differentiated players according to their playing position, with better bilateral symmetry among guards (F-test = 6.11 (medium effect size) and 5.81 (small effect size), p < 0.05 for lay-up and running-jump symmetry, respectively). Performance levels significantly differed in the bilateral symmetry of lay-up jump, with better symmetry for first-division players (F-test = 10.11 (medium effect size), p < 0.001), which was mostly influenced by significant differences among guards. Playing positions and performance levels did not differ in bilateral symmetry of the CODS and RAG. The study reveals the importance of bilateral symmetry of the sport-specific performance in differentiating playing positions and performance levels in basketball. Further studies in other multidirectional sports and other sport-specific performances are warranted.

Quantification of Inter-Limb Symmetries With Rate of Force Development and Relaxation Scaling Factor

The inter-limb (a)symmetries have been most often assessed with the tests that quantify the maximal muscle capacity. However, the rapid force production and relaxation during submaximal tasks is equally important for successful sports performance. This can be evaluated with an established rate of force development and relaxation scaling factor (RFD-SF/RFR-SF). The aims of our study were (1) to assess the intra-session reliability of shortened RFD-SF/RFR-SF protocol and its absolute and symmetry outcome measures, (2) to compare the main absolute RFD-SF/RFR-SF outcome measures (slopes of RFD-SF and RFR-SF: kRTD-SF and kRFR-SF, theoretical peak RFD/RFR: TPRFD and TPRFR) across gender and sports groups, and (3) to compare inter-limb symmetries across gender and sports groups for main outcome measures (kRFD-SF, kRFR-SF, TPRFD, and TPRFR). A cross-sectional study was conducted on a group of young health participants (basketball and tennis players, and students): 30 in the reliability study and 248 in the comparison study. Our results showed good to excellent relative and excellent absolute reliability for the selected absolute and symmetry outcome measures (kRFD-SF, kRFR-SF, TPRFD, and TPRFR). We found significantly higher absolute values for kRFD-SF and TPRFD in males compared to females for the preferred (kRFD-SF: 9.1 ± 0.9 vs. 8.6 ± 0.9/s) and the non-preferred leg (kRFD-SF: 9.1 ± 0.9 vs. 8.5 ± 0.8/s), while there was no effect of sport. Significantly lower symmetry values for kRFR-SF (88.4 ± 8.6 vs. 90.4 ± 8.0%) and TPRFR (90.9 ± 6.8 vs. 92.5 ± 6.0%) were found in males compared to females. Moreover, tennis players had significantly higher symmetry values for kRFR-SF (91.1 ± 7.7%) and TPRFR (93.1 ± 6.0%) compared to basketball players (kRFR-SF: 88.4 ± 8.7% and TPRFR: 90.9 ± 6.7%) and students (kRFR-SF: 87.6 ± 8.7% and TPRFR: 90.5 ± 6.7%). Our results suggest that the reduced RFD-SF/RFR-SF protocol is a valuable and useful tool for inter-limb (a)symmetry evaluation. Differences in symmetry values in kRFR-SF and TPRFR (relaxation phase) were found between different sports groups. These may be explained by different mechanisms underlying the muscle contraction and relaxation. We suggest that muscle contraction and relaxation should be assessed for in-depth inter-limb symmetry investigation.

Bilateral deficit in countermovement jump and its association with change of direction performance in basketball and tennis players

The purpose of this study was to assess the association between bilateral deficit (BLD) in countermovement jump and change of direction (CoD) performance. Therefore, 165 young basketball players (60 females) and 95 young tennis players (39 females) performed two different CoD tasks (90° and 180° turns) and bilateral and unilateral countermovement jumps. BLD was calculated based on jump height, peak power and several phase-specific force impulses (FI). For male athletes, several statistically significant small to moderate associations were found between the CoD performance and BLD (r = 0.21-0.52). While the BLD in the propulsive phase FI seems to be most consistently associated with CoD performance, all associations were weak (r = 0.21-0.28 in basketball, 0.28-0.36 in tennis). Associations between BLD in total positive (braking and propulsive phase) FI and CoD performance were moderate (r = 0.45-0.52) in male tennis players. For female athletes, the associations were even smaller and almost exclusively statistically non-significant. Although indirectly, our results imply that resistance training based on unilateral exercises could be useful to improve CoD performance. It has to be stressed that further training studies are needed to directly confirm this assumption.

Comparison between gymnasts and non-gymnasts in isometric strength of the lower limbs

Muscle asymmetries in gymnasts are common and can lead to injury. We aimed to determine differences in hip, knee, and ankle strength between female gymnasts and non-gymnasts, and secondly, to determine the effect of strength training intervention. Fifteen gymnasts (aged 11.19 ± 1.89 years) and 15 non-gymnasts (aged 10.92 ± 1.96 years) performed unilateral isometric maximal voluntary contractions of the hip (extensor, flexor, abductor, adductor, internal and external rotator), knee and ankle flexors and extensors on a dynamometer. Inter-limb asymmetries (ILAs) were compared across strength outcomes (MVC torque) and groups. ILAs was calculated based on the strength measurements. The gymnasts were retested after 8 weeks, during which the participants performed 5 weeks of regular training and 3 weeks of targeted strength training intervention. We found significant differences between groups in most observed hip strength parameters, but not in knee and ankle strength. The intervention did not significantly affect any parameter of ILAs. Gymnasts and non-gymnasts differ in hip strength parameters. A longer intervention program may decrease ILA parameters.

Influence of Load and Phase of Contraction on Lateral Symmetries in Flywheel Squats

Assessment of lateral symmetries (LS) of lower limbs has been widely investigated. However, there are no studies about LS during exposure to high eccentric and concentric loads during flywheel (FW) squats. A total of 422 young, physically active participants performed squats on an FW device with different equidistant loads (0.05, 0.125 and 0.2 kg∙m2). The mean and peak force of the left and right leg were assessed for the concentric and eccentric contaction phase. LS values were calculated for each load and phase of squat. Our results showed that the absolute mean and peak force of the concentric and eccentric phase of contraction had excellent reliability, while LS values were more reliable when eccentric force was used for their calculation. Mean and peak forces were increased with the higher FW load. In general, we found a decrease in LS values in the concentric phase of contraction with the higher load. Moreover, values of LS are similar to a wide range of other functional movements. Nevertheless, symmetrical force application during squatting on a FW device should be satisfied regardless of the FW load. Due to the large sample size, our results are valuable as a reference point when athletes are evaluated during training.