Angle-Specific Isokinetic Metrics Highlight Strength Training Needs of Elite Youth Soccer Players

The influence of menstrual cycle phase on isokinetic knee flexor and extensor strength in female soccer players: a pilot study

The prevalence of anterior cruciate ligament injury in female soccer players has been attributed to hormonal fluctuations during the menstrual cycle (MC), with injury incidence greatest during the follicular phase. Eight, eumenorrheic, collegiate soccer players (19.5 ± 0.75 years, 1.62 ± 4.90 cm, 61.12 ± 7.6 kg mean ± SD) completed eccentric knee flexor and concentric knee extensor trials at 60 and 240°·s-1 during the follicular, ovulation and luteal phases of their MC. Peak torque and corresponding angle of peak torque were maintained across all phases of the MC, irrespective of testing modality and speed (p ≥ 0.149). Strength ratios defined using peak torque were also not sensitive to MC phase (p ≥ 0.933). However, Functional Range in eccentric knee flexion was significantly lower during the follicular phase (p = 0.017), at both testing speeds. This supports epidemiological observations but highlights the importance of analysing isokinetic data beyond the peak of the strength curve. Interpretation of isokinetic data should therefore focus on points of "weakness" as opposed to maximum strength, whilst (p)rehabilitative strategies should consider strength through range of motion, and at different speeds. Eccentric hamstring strength was observed to decrease significantly at the higher speed, contrary to observations in elite male players, and potentially reflecting a differential training adaptation.

Assessment of Strength and Power Capacities in Elite Male Soccer: A Systematic Review of Test Protocols Used in Practice and Research

BACKGROUND

Strength and power represent two crucial physical qualities for the attainment of a high level of performance considering the frequency and the importance of explosive actions occurring during elite soccer match-play. Evaluation of strength and power is a multifaceted concept involving a vast array of tests and outcome variables. Nevertheless, a comprehensive and systematic search of strength and power assessment procedures in elite soccer has yet to be undertaken.

OBJECTIVES

The aims of this systematic review were to: (1) identify the tests and outcome variables used to assess strength and power of elite male soccer players; (2) provide normative values for the most common tests of strength and power across different playing levels; and (3) report the reliability values of these strength and power tests.

METHODS

A systematic review of the academic databases MEDLINE, CINAHL, SPORTDiscus, Web of Science and OVID for studies published until August 2023 was conducted, following the Preferred Reporting Items of Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Studies were eligible for inclusion if they: (1) were original research studies, published in a peer-reviewed journal, and written in English language; (2) had the primary aim to assess strength and/or power; (3) players were male and older than 17 years of age (i.e., mean age of the group); and (4) their playing level was defined as "professional", "international" or "elite".

RESULTS

Regarding strength testing, 115 studies and 29 different tests were identified. The three most frequent strength tests were the knee extensor isokinetic strength test (58 studies), the knee flexor isokinetic strength test (55 studies) and the Nordic hamstring strength test (13 studies). In terms of power testing, 127 studies with 31 different tests were included. The three most frequent power tests were the countermovement jump with hands fixed on hips (99 studies), the squat jump (48 studies) and the vertical jump with arm swing (29 studies).

CONCLUSIONS

The wide range of different tests and outcome variables identified in this systematic review highlights the large diversity in the employed testing procedures. The establishment of a hybrid testing approach, combining standardised and widely accepted tests for establishing normative standards and enabling comparisons across different contexts, with flexible context-specific testing batteries, has the potential to maximise the impact of testing information for practitioners. In addition, the limited reporting of reliability data across studies highlights the need for practitioners to establish their own reliability measure within their specific contexts, informing the selection of certain tests and outcome variables.

Intra- and inter-limb strength imbalance and asymmetry in soccer: A comparison of elite senior and junior players

Evaluation of muscle strength imbalance can be an important element in optimizing the training process of soccer players. The purpose of the study was to examine isokinetic peak torque (PT) and total work (TW) exerted by both knee extensors (quadriceps or Q) and flexors (hamstrings or H), intra-limb imbalance and the magnitude and direction of inter-limb asymmetry in top elite senior (n = 109) and junior (n = 74) soccer players. An isokinetic dynamometry was used to measure maximum peak torque of quadriceps (PT-Q) and hamstrings (PT-H) at an angular velocity of 60° ·s-1, as well as the total work for extensors (TW-Q) and flexors (TW-H) at an angular velocity of 240° ·s-1 in the dominant (DL) and non-dominant leg (NDL) during concentric muscle contraction. Intra-limb imbalance and inter-limb asymmetries were calculated using a standard equation. Statistical analysis using t-test and Mann-Whitney U-test revealed: (a) no differences (p > 0.05) between groups for PT-Q and PT-H, (b) greater strength levels (p < 0.05) for TW-Q and TW-H of senior players than juniors, and (c) no differences (p > 0.05) between groups for intra-limb imbalance and inter-limb asymmetry. Additionally, Pearson's chi-kwadrat (χ2) analysis showed no differences (p > 0.05) between groups for intra-limb imbalance and inter-limb asymmetry in relation to the 'normative' values accepted in the literature that indicate an increase in the risk of knee injury. This study shows that isokinetic assessment can be an important tool to identify imbalances/asymmetries and to develop strategies to reduce the risk of muscle injury.

Evaluation of muscular and functional inter-limb asymmetries during mid-season in young male soccer athletes

BACKGROUND

To identify inter-limb asymmetries through the knee's muscular and lower limb functional performance in young male soccer athletes.

METHODS

Twenty male soccer athletes aged 17 to 19 from an under-20 team performed isokinetic tests at 60°/s., 120°/s., 180°/s., and 240°/s. To assess the knee extensors and flexors muscles and functional tests (hop tests and Y-balance test).

RESULTS

There were no significant differences between the dominant limb (DL) and non-dominant limb (NDL) in the knee extensors and flexors peak torque and hamstrings (H)/quadriceps(Q) conventional ratio. Moreover, no angular velocities observed inter-limb asymmetries seen by values higher than 10% in the isokinetic parameters. However, the H/Q conventional ratio shows borderline values in low angular velocities (60°/s. and 120°/s.). No significant changes were observed in the functional test performance between the DL and NDL. Furthermore, we did not see inter-limb asymmetries in both hop and Y-balance tests. On the contrary, the anterior distance reached was lower than found in the literature, and the composite score of the Y-balance test demonstrated values below the normative (>94%).

CONCLUSION

The data demonstrated that soccer athletes have muscular and functional inter-limb symmetry. However, they tend to have knee muscle imbalance in low velocities and dynamic balance deficits that might increase the risk of musculoskeletal injury.

The influence of isokinetic dynamometer configuration on eccentric hamstring strength metrics: implications for testing and training

Isokinetic dynamometry is the clinical gold standard for strength assessment but testing protocols and outcome metrics can lack functional relevance. To quantify the influence of dynamometer configuration on eccentric hamstring strength metrics, 23 trained participants completed isokinetic eccentric knee flexor trials at 180°·s-1 in a seated and extended hip position. The extended position elicited a greater peak torque (P = 0.04) which was achieved at a significantly (P < 0.001) greater degree of knee flexion. Isokinetic range and functional range (defined as 85% of peak torque) were consistent at ~44° and ~21°, respectively, across trials, but were achieved with a more flexed knee in the extended hip configuration. Therefore, whilst the extended hip configuration might better reflect the biarticular nature of the hamstring musculature and the mechanism of hamstring strain injury, the sensitivity of strength metrics to configuration has implications for clinical assessment and training adaptations.

Hamstrings force-length relationships and their implications for angle-specific joint torques: a narrative review

Temporal biomechanical and physiological responses to physical activity vary between individual hamstrings components as well as between exercises, suggesting that hamstring muscles operate differently, and over different lengths, between tasks. Nevertheless, the force-length properties of these muscles have not been thoroughly investigated. The present review examines the factors influencing the hamstrings’ force-length properties and relates them to in vivo function. A search in four databases was performed for studies that examined relations between muscle length and force, torque, activation, or moment arm of hamstring muscles. Evidence was collated in relation to force-length relationships at a sarcomere/fiber level and then moment arm-length, activation-length, and torque-joint angle relations. Five forward simulation models were also used to predict force-length and torque-length relations of hamstring muscles. The results show that, due to architectural differences alone, semitendinosus (ST) produces less peak force and has a flatter active (contractile) fiber force-length relation than both biceps femoris long head (BFlh) and semimembranosus (SM), however BFlh and SM contribute greater forces through much of the hip and knee joint ranges of motion. The hamstrings’ maximum moment arms are greater at the hip than knee, so the muscles tend to act more as force producers at the hip but generate greater joint rotation and angular velocity at the knee for a given muscle shortening length and speed. However, SM moment arm is longer than SM and BFlh, partially alleviating its reduced force capacity but also reducing its otherwise substantial excursion potential. The current evidence, bound by the limitations of electromyography techniques, suggests that joint angle-dependent activation variations have minimal impact on force-length or torque-angle relations. During daily activities such as walking or sitting down, the hamstrings appear to operate on the ascending limbs of their force-length relations while knee flexion exercises performed with hip angles 45–90° promote more optimal force generation. Exercises requiring hip flexion at 45–120° and knee extension 45–0° (e.g. sprint running) may therefore evoke greater muscle forces and, speculatively, provide a more optimum adaptive stimulus. Finally, increases in resistance to stretch during hip flexion beyond 45° result mainly from SM and BFlh muscles.

Knee and hip agonist-antagonist relationship in male under-19 soccer players

The purpose of this study was to evaluate the strength of the knee flexors and extensors and hip abductor and adductor muscles in young soccer players. Twenty-three male under-19 soccer players participated in this study (age: 17.7 ± 0.2 years; height: 173.0 ± 1.1 cm; body mass: 66.1 ± 1.3 kg). Body composition was measured using a bioelectrical impedance (InBody770), and the dynamometry was performed by an isokinetic dynamometer (Biodex System 3) for knee flexion and extension, and by an isometric dynamometer (Smart Groin Trainer), for hip adduction and abduction. Comparisons were made between dominant members (D) vs. non-dominant members (ND) and adductors vs. abductors (ADD:ABD) using the Wilcoxon test. There were statistically significant differences in the peak torques between the dominant and non-dominant members in the flexion function (Z = −4.198, p < 0.01) and in the extension function (Z = −4.197, p < 0.01) of the knee in concentric muscular action, and the flexion (Z = −4.198, p < 0.01) and in the extension (Z = −4.198, p < 0.01) of the knee in eccentric muscular action. No statistically significant differences were obtained in the conventional ratio (Z = −0.456, p = 0.648) nor the functional ratio (Z = −0.335, p = 0.738) between D and ND members. There were no statistically significant differences between adductors and abductors at the moment of strength for absolute values (N). The reference absolute and normalized to the weight values and the ADD:ABD can be used as a guideline for classifying players in screening and comparison in return tests to sports practice after an injury.

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.

Can 3 mg·kg-1 of Caffeine Be Used as An Effective Nutritional Supplement to Enhance the Effects of Resistance Training in Rugby Union Players?

The present study uniquely examined the effect of 3 mg·kg⁻¹ chronic caffeine consumption on training adaptations induced by 7-weeks resistance training and assessed the potential for habituation to caffeine’s ergogenicity. Thirty non-specifically resistance-trained university standard male rugby union players (age (years): 20 ± 2; height (cm): 181 ± 7; body mass (kg): 92 ± 17) completed the study), who were moderate habitual caffeine consumers (118 ± 110 mg), completed the study. Using a within-subject double-blind, placebo-controlled experimental design, the acute effects of caffeine intake on upper and lower limb maximal voluntary concentric and eccentric torque were measured using isokinetic dynamometry (IKD) prior to and immediately following a resistance training intervention. Participants were split into strength-matched groups and completed a resistance-training program for seven weeks, consuming either caffeine or a placebo before each session. Irrespective of group, acute caffeine consumption improved peak eccentric torque of the elbow extensors (p < 0.013), peak concentric torque of the elbow flexors (p < 0.005), total eccentric work of the elbow flexors (p < 0.003), total concentric work of the knee extensors (p < 0.001), and total concentric and eccentric work of the knee flexors (p < 0.046) following repeated maximal voluntary contractions. Many of these acute caffeine effects were still prevalent following chronic exposure to caffeine throughout the intervention. The training intervention resulted in significant improvements in upper and lower body one-repetition maximum strength (p < 0.001). For the most part, the effect of the training intervention was equivalent in both the caffeine and placebo groups, despite a small but significant increase (p < 0.037) in the total work performed in the participants that consumed caffeine across the course of the intervention. These results infer that caffeine may be beneficial to evoke acute improvements in muscular strength, with acute effects prevalent following chronic exposure to the experimental dose. However, individuals that consumed caffeine during the intervention did not elicit superior post-intervention training- induced adaptations in muscular strength.

Assessing thigh muscle balance of male athletes with special emphasis on eccentric hamstring strength

Background: Hamstring strength is important to prevent thigh muscle and knee injuries. Different antagonist-agonist relationships of thigh muscle strength are applied to estimate the injury risk e.g. the intersection point of eccentric hamstring (Hecc) and concentric quadriceps (Qcon) moment-knee flexion angle curves (dynamic control ratio at the equilibrium point = DCRe) and the dynamic control ratio (DCR = Hecc:Qcon). Objective: The aim was to quantify the relationships between DCR, DCRe moments and angles as well as their correlations with peak moments and contractional work of eccentric hamstring and concentric quadriceps exercise. Methods: This cross-sectional study included data from 238 healthy male participants of different sports. They conducted unilateral isokinetic tests obtained at 30°/s and 150°/s for the hamstrings (prone) and the quadriceps (supine). Results: Correlations between DCR and DCRe moments were significant, but weak to moderate in strength (R²_30°/s = 20%, R²_150°/s = 26%). In contrast to DCR (25% ≤ R² ≤ 46%), DCRe moments (80% ≤ R² ≤ 86%) showed very strong relations with peak moments and contractional work of eccentric hamstring exercise. Discussion: DCR and DCRe assess thigh balance by using the same isokinetic raw data. However, weak relations became apparent. DCRe moments were stronger related to eccentric hamstring strength and work than DCR. Therefore, the DCRe moment may serve as meaningful measure of thigh muscle balance because increased eccentric hamstring strength promotes dynamic joint stability and minimizes injury risk.

The cumulative and residual changes in eccentric knee flexor strength indices following soccer-specific treadmill running: Novel considerations of angle specific torque

With potential implications for recovery and conditioning practices, the aim of this study was to assess the cumulative and residual response of angle specific eccentric knee flexor (eccKF) strength indices following soccer-specific activity. Thirteen semi-professional soccer players were therefore required to complete a 90-minute soccer-specific treadmill running. with eccKF isokinetic strength assessments completed pre-trial, immediately post-trial, and 48 hours post-trial. The strength assessments comprised the completion of 5 repetitions at angular velocities of 60 and 300 deg·s^-1. Isokinetic data was analysed for measures of peak torque (PT), angle of peak torque (APT), functional range (FR), and angle specific torque (AST). Significant post-trial impairments were observed for measures of slow velocity PT₆₀ (6.6%) and AST₃₀₀ (12.5%). Further significant differences were observed 48 hours post-trial for PT₃₀₀ (10.7%) and PT₆₀ (12.8%) PT, APT₆₀ (~15°), and AST₃₀₀ (>13.6%). These data have implications for post exercise recovery monitoring and the prescription of recovery modalities and conditioning practices in the 2 days following match-play. The AST and APT responses highlight the importance of analysis of the entire strength-angle curve and at a range of angular velocities.

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.

The association between the isokinetic muscle strength and lower extremity injuries in young male football players

BACKGROUND

Validating any screening test to predict and prevent football injuries is in need of identifying related risk factors through prospective designs. In spite of the extensive use of strength testing in football players, there are limited studies investigating the relationship between isokinetic muscle strength and injury risk in young football players. The present study aimed to evaluate the relationship between isokinetic strength and the risk of lower extremity injury among Iranian young football players.

METHOD

ology: seventy three U-21 football players participated in this study. Isokinetic strength of hip, knee and ankle muscles were measured using the Isokinetic system pro 4. Injuries and exposure in training and matches were registered prospectively by club medical staff for one season.

RESULTS

Significant relationships were revealed between the isokinetic strength of hip abductor and adductor muscles, and isokinetic strength ratio of hip abductor/adductor muscles at an angular speed of 30°/sec, the isokinetic strength of hip abductor muscles at 90°/sec, and isokinetic strength of knee flexor and extensor muscles at 60°/sec and knee flexor/extensor strength ratio at angular velocities of 60°/sec with the injury occurrence among football players.

CONCLUSION

lower extremity isokinetic strength indices are associated with injuries in young male football players.

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

OBJECTIVES

To compare traditional and angle-specific isokinetic strength of eccentric knee flexors and concentric knee extensors in female senior professional and youth soccer players.

DESIGN

Cross-sectional study design.

SETTING

University's Laboratory.

PARTICIPANTS

A total of 34 players (17 seniors [age 25.31 ± 4.51 years; height 167.89 ± 7.04 cm; mass 63.12 ± 7.79 kg] and 17 youths [16.91 ± 1.16 years; height 165.92 ± 4.42 cm; mass 60.07 ± 4.48 kg]) from the Women's Super League 1 completed strength assessments at 180, 270 and 60°∙s^-1.

MAIN OUTCOME MEASURES

Peak torque (PT), dynamic control ratio (DCR), angle of peak torque (APT), functional range (FR), angle-specific torque (AST) and angle-specific DCR (DCR_AST) were compared between age groups.

RESULTS

The PT (P = 0.016) AST (P = 0.041) were significantly higher in seniors compared to youths; however APT (P = 0.141), DCR (P = 0.524) FR (P = 0.821) and DCR_AST (P = 0.053) were not significant between playing age.

CONCLUSION

The use of absolute and angle-specific strength measures were able to distinguish between female playing ages, whereas DCR and DCR_AST was unable to identify differences. The PT and AST metrics may be the most useful metrics to help identify and inform training needs, particularly in youths.

Alternative Methods of Determining Hamstrings-to-Quadriceps Ratios: a Comprehensive Review

The hamstrings-to-quadriceps muscle strength ratio calculated by peak torque has been used as an important tool to detect muscle imbalance, monitor knee joint stability, describe muscle strength properties and functionality, and for lower extremity injury prevention and rehabilitation. However, this ratio does not consider other neuromuscular variables that can also influence the antagonist to agonist muscle relationship, such as torque produced at multiple angles of range of motion, explosive strength, muscle size, muscle fatigue, or muscle activation. The aim of this study was to comprehensively review alternative methods of determining the hamstrings-to-quadriceps ratio. These include ratios calculated by angle-specific torque, rate of torque development, muscle size, fatigue index, and muscle activation (measured by electromyography). Collectively, the literature demonstrates that utilizing alternative methods of determining the hamstrings-to-quadriceps ratio can be functionally relevant for a better understanding of the neuromuscular mechanisms underpinning the interaction of strength between hamstrings and quadriceps. However, there is insufficient evidence to recommend any of the alternative methods as sensitive clinical tools for predicting injury risk and monitoring knee joint integrity. Future longitudinal studies, along with injury incidence, are needed to further investigate all alternative methods of determining the hamstrings-to-quadriceps ratio. These have potential to offer insight into how athletes and the general population should be trained for performance enhancement and injury reduction, and may be used along with traditional methods for a thorough assessment of an individual’s H:Q muscle balance.