Isokinetic strength differences between elite senior and youth female soccer players identifies training requirements

Reliability of lower limb strength assessment in female team sport athletes

BACKGROUND

Lower limb injury rates have increased dramatically in line with increased female sport participation levels. Muscle strength is a modifiable lower limb injury risk factor, guiding performance monitoring and rehabilitation.

OBJECTIVES

The aim of this study was to investigate the test-retest reliability of isokinetic and isometric lower limb peak torque to body mass of muscles acting on the hip, knee, and ankle in female team sport athletes. It was hypothesised the test-retest reliability would be good (intraclass correlation coefficients (ICC) ≥ 0.75).

METHODS

Thirty-eight female athletes (Australian Rules Football = 18, netball = 12, soccer = 8) aged 16-35 years participated in this study. Participants performed isokinetic (60°/s and 120°/s) and isometric testing on a Biodex Isokinetic Dynamometer on three separate days.

RESULTS

Poor to good reliability was demonstrated for all joint movements (ICC = 0.38-0.88) with small to moderate effect sizes (0.00-0.43) and typical errors (5.65-24.49).

CONCLUSION

Differences in peak torque to body mass were observed between sessions one and two and/or one and three, demonstrating a learning effect. Therefore, three testing sessions, and/or the inclusion of a familiarisation session, is recommended for future assessments in populations unfamiliar with dynamometry.

The association between unilateral and bilateral performance-related measures in elite female soccer players: a multifaceted investigation

Purpose

The present study aimed to investigate a) the associations between bilateral performance utilizing countermovement jump (CMJ), squat jump (SJ), speed and unilateral CMJ, isokinetic peak torque in knee extension and flexion with angular velocities of 60°/s and 180°/s and tensiomyography (TMG) parameters; b) whether the asymmetries derived from unilateral tests are associated with bilateral CMJ, SJ and speed in elite female soccer players.

Methods

Thirty-five elite female soccer players (average age: 20 ± 5 years) completed CMJ, SJ, speed, isokinetic muscle strength and TMG tests.

Results

Compared to the non-dominant leg, the dominant leg demonstrated greater peak torque output in both knee flexion (7.4%) and knee extension (5.6%) isokinetic tasks, as well as m. vastus medialis contraction time (7.6%), and soccer-specific agility test (4.1%). Conversely, the hamstring to quadriceps peak torque ratio at 180°/s (8.5%) was significantly greater in the non-dominant leg. The associations between CMJ, SJ and speed performance were positive and ranged from weak (r = 0.350) to high (r = 0.710). For speed and TMG-derived variables, correlations were negative and ranged from weak (r = -0.345, p = 0.042, for vastus medialis contraction time) to moderate (r = -0.530, p = 0.001, for biceps femoris contraction time). Furthermore, both bilateral CMJ and SJ negatively correlated with TMG-derived variables, ranging from weak (r = -0.350, p = 0.039, for vastus lateralis contraction time) to moderate (r = -0.537, p = 0.003, for rectus femoris contraction time).

Conclusion

The overall significant, albeit inconsistent, correlations between the diverse performance scores obtained highlight the necessity for a multifaceted and thorough diagnostic strategy in female soccer players.

Learning effect on an isokinetic knee strength test protocol among male adolescent athletes

Learning effect occurs when the best performance is not achieved at the earliest trial of a repeated protocol of evaluation. The present study examined, within testing session, the intra-individual variation in an isokinetic strength protocol composed of five reciprocal concentric and eccentric contractions of knee extensors (KE) and knee flexors (KF) among male adolescent swimmers. Additionally, test-retest reliability was determined as intra-individual mean differences between two consecutive testing sessions. The sample included 38 swimmers aged 10.1-13.3 years. A subsample (n = 17) completed a second visit. Isokinetic dynamometry was used to assess concentric and eccentric contractions of KE and KF at an angular velocity of 60°.s-1. The protocol included three preliminary repetitions that were not retained for analysis, a 60-second interval, and five reciprocal maximal concentric contractions (cc). The preceding sequence was repeated for eccentric contractions (ecc) of KE and KF. Multilevel regression confirmed intra-individual and inter-individual levels as significant sources of variance in peak torque (PT) values. Intra-class correlation (ICC) fluctuated between 0.582 and 0.834 and, in general, a substantial percentage of participants need more than three repetitions to attain their best PT: KEcc (36.8%), KEecc (23.7%), KFcc (39.5%), KFecc (18.4%). For the subsample of 17 swimmers who completed a second testing session, intra-individual mean differences of the best PT were trivial or small. In summary, the validity of shorter protocols may be compromised if swimmers do not attain their best peak torque in the first few attempts, and the reliability of a 5-repetition protocol seemed acceptable.

Isokinetic profiling of elite youth footballers: informing selection of a practicable and efficacious isokinetic screening test

Isokinetic dynamometry represents the clinical gold standard for strength assessment but testing lack consensus. Elite youth male football players (n = 28) completed 20 repetitions (analysed as four epochs) of eccentric knee flexor (eccKF) and concentric knee extensor (conKE) trials at 60, 180 and 270°∙s^-1, quantifying peak torque (PT) and functional range (FR). There was a significant (P < 0.001) main effect for fatigue and angular velocity in conKE PT; eccKF PT was not significant across epoch (P = 0.35) and velocity (P = 0.12) and a velocity x epoch interaction highlighted more repetitions were required to elicit fatigue as velocity increased. FR decreased with fatigue (P < 0.001) and velocity (P < 0.01) in conKE and eccKF, indicative of a narrowing of the strength curve. Clinical interpretation advocates an isokinetic test comprising at least 15 reps at a velocity ≥ 180°∙s^-1 and analysis beyond the peak of the strength curve (PT) to inform clinical reasoning and individualized exercise prescription.

Knee Isokinetic Profiles and Reference Values of Professional Female Soccer Players

Few studies have previously evaluated isokinetic parameters in female soccer players in comparison to those in males. The aim of this study was to describe normative quadriceps (Q) and hamstring (H) muscle strength values in professional female soccer players and to examine differences between dominant leg (DL) and nondominant leg (NDL). A standardized test protocol of concentric knee extension and flexion test protocol was conducted using the dynamometer isokinetic system (IsoMEd 2000). All the participants were healthy female professional soccer players from Spanish first and second division teams. Players were assessed for peak torque (PT) and maximum work (MW) values at 60°/s, 180°/s, and 240°/s. The mean difference was 7.17 (p-value = 0.0036), 4.4 (p-value = 0.0386), and 4.25 Nm (p-value = 0.0241) at speed 60°, 180°, and 240°/s, respectively. No statistically significant differences were detected for H-Q values between DL and NDL. This difference was 6.44 (p-value = 0.0449), and 5.87 J (p-value = 0.0266) at speed 60°, and 180°/s. The present study can be a tool that health professionals working with female professional soccer players in their care can use to assess and monitor a particular player.

The influence of angle-specific torque of the knee flexors and extensors on the angle-specific dynamic control ratio in professional female soccer players

The purpose of this study was to assess whether dynamic torque ratios (DCR) from isokinetic strength assessments of eccentric knee flexors (eccKF) and concentric knee extensors (conKE) display differences when stratified into specific angle-specific DCR (DCR_AST) groups. Fifty-two professional female soccer players (age 21.30 ± 4.44 years; height 166.56 ± 5.17 cm; mass 61.55 ± 5.73 kg) from the English Women's Super League completed strength assessments of both lower limbs on an isokinetic dynamometer at 60°∙s^-1. Angle-specific torque (AST) were used to calculate DCR_AST to create sub-groups using clustering algorithms. The results identified for the dominant side that the Medium DCR_AST group elicited significantly higher conKE AST when compared to Low and High DCR_AST groups at increased knee extension (P ≤ 0.05). For the non-dominant side, the High DCR_AST group had significantly higher and lower eccKF and conKE AST compared to the Low DCR_AST group at increased knee extension (P ≤ 0.05). This study highlights that the inclusion of AST data may subsequently help practitioners to prescribe exercise that promotes strength increases at targeted joint angles. In turn, these approaches can be used to help reduce injury risk, identify rehabilitation responses and help inform return to play.

Sprint mechanical properties of professional rugby league players according to playing standard, age and position, and the association with key physical characteristics

BACKGROUND

This study determined the influence of playing standard, age, and position on the horizontal force-velocity (FV) properties of rugby league players, and the association with other characteristics.

METHODS

This observational study used a cross-sectional design with a range of physical characteristics recorded from 132 players from 5 Super League clubs. Sprint data was used to derived theoretical maximal force (F0) and velocity (V0), power (Pmax), maximal rate of force (RFmax) and the rate of decrease in RFmax (DRF). Differences between playing standard, age groups and playing positions were determined (P value and standardised mean difference (SMD) along with correlational analysis to assess the relationship between FV properties and key physical characteristics.

RESULTS

Senior players reported lower split time (SMD = -0.26--0.59, P =0.002-0.017), absolute F0, Pmax and V0 (SMD = 0.47-0.78, P <0.001-0.010). Players aged <21 years reported higher split times and lower absolute F0 compared to 21-26 years (SMD = -0.84--0.56, P <0.001-0.04) and a lower V0 than >26 years (SMD = -0.40, P=0.002). Hit-up forwards were slower than outside backs (SMD = -0.30--0.89, P <0.001-0.042), though produced the highest absolute F0 and Pmax. Split times F0, V0, Pmax and RFmax were associated with change of direction and countermovement jump performance, whilst FVslope and DRF were associated with countermovement jump performance. F0 and Pmax were associated with medicine ball throw distance (r = 0.302-0371, P = ≤0.001). There was no association with prone Yo-Yo IR1 distance (r = -0.16-0.09, P =0.060-0.615).

CONCLUSIONS

These results provide insight into the horizontal FV properties with reference to key sub-groups, and highlights several associations with other characteristics across large sample of rugby league players. The result of this study should be used when interpreting the sprint ability of rugby league players, planning the long-term development of youth players, and inform programme design for all.

Differences in the vertical and horizontal force-velocity profile between academy and senior professional rugby league players, and the implications for strength and speed training

BACKGROUND

This study compared the vertical and horizontal force-velocity (FV) profile of academy and senior rugby league players.

METHODS

Nineteen senior and twenty academy players from one professional club participated in this study. The vertical FV profile was determined using a series of loaded squat jumps (0.4 to 80 kg) with jump height recorded. The horizontal FV profile involved a 30-m over-ground sprint with split times recorded at 5, 10, 15, 20 and 30 m. Theoretical maximal force (F0), velocity (V0) and power (Pmax), optimal F0 and V0, and activity specific variables (e.g. vertical FV imbalance) were determined.

RESULTS

Absolute F0 and Pmax from the vertical and horizontal profile were moderately different between groups (standardised mean difference (SMD) = 0.64-1.20, P <0.001-0.026), whilst for V0, differences were small (SMD = 0.33-0.41, P = 0.149-0.283). Differences in relative F0, Pmax and optimal F0 during both assessments were trivial to moderate (SMD = 0.03-0.82, P = 0.021-0.907).

CONCLUSIONS

These results highlight senior and academy players present with different FV profiles and highlight some potential developmental opportunities for senior and academy rugby league players that sport scientists, strength and conditioning and rugby coaches can implement when designing programmes and considering long-term athlete development.

Eccentric Resistance Training in Youth: Perspectives for Long-Term Athletic Development

The purpose of this narrative review is to discuss the role of eccentric resistance training in youth and how this training modality can be utilized within long-term physical development. Current literature on responses to eccentric exercise in youth has demonstrated that potential concerns, such as fatigue and muscle damage, compared to adults are not supported. Considering the importance of resistance training for youth athletes and the benefits of eccentric training in enhancing strength, power, speed, and resistance to injury, its inclusion throughout youth may be warranted. In this review we provide a brief overview of the physiological responses to exercise in youth with specific reference to the different responses to eccentric resistance training between children, adolescents, and adults. Thereafter, we discuss the importance of ensuring that force absorption qualities are trained throughout youth and how these may be influenced by growth and maturation. In particular, we propose practical methods on how eccentric resistance training methods can be implemented in youth via the inclusion of efficient landing mechanics, eccentric hamstrings strengthening and flywheel inertia training. This article proposes that the use of eccentric resistance training in youth should be considered a necessity to help develop both physical qualities that underpin sporting performance, as well as reducing injury risk. However, as with any other training modality implemented within youth, careful consideration should be given in accordance with an individual's maturity status, training history and technical competency as well as being underpinned by current long-term physical development guidelines.