Are There Differences in Concentric Isokinetic Strength Perfor-Mance Profiles between International and Non-International Elite Soccer Players?

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.

Knee and Hip Muscle Strength of Male Soccer Players from Different Competitive Levels

In soccer, knee and hip muscle strength assessments have been recommended for injury prevention. The aims of this study were threefold: (1) to compare knee and hip muscle strength between professional players competing at different levels; (2) to compare strength performance according to the preferred leg (PL) and the non-preferred leg (NPL); and (3) to compare knee and hip muscle strength performance at two moments of the season. This study included 33 professional soccer players: 13 were in the elite group (EG), and 20 were in the sub-elite group (SEG). Body composition, isokinetic knee strength at 60º/s, and hip adduction strength were assessed at two different moments (M1 and M2). Values of peak torque (PT), peak torque/bodyweight (PT/BW), and the hamstring-to-quadriceps strength ratio (H:Q) for knee extensors (KEs) and knee flexors (KFs) for both legs were used for analysis. The statistical analysis included the Mann-Whitney U and the Wilcoxon Signed Rank tests. At M1, the EG presented a significantly better performance in KF PT/BW and in the squeeze strength test for the PL and the NPL (p ≤ 0.01). At M2, the EG performed substantially better in KE PT/BW and KF PT/BW (p ≤ 0.01). No substantial strength differences were observed in knee and hip muscle performance between the PL and the NPL. From M1 to M2, significant increases were found in knee strength in both groups (p ≤ 0.01). Overall, the EG players outperformed significantly their lower-division peers in strength assessments. The results indicate significant knee and hip muscle strength increases during the season, probably as a response to the exposure to training and competition.

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 Relationship between the Hamstring-to-Quadriceps Ratio and Jumping and Sprinting Abilities of Young Male Soccer Players

The correct torque ratio between the knee joint extensor and flexor muscle groups can effectively prevent injuries to the anterior cruciate ligament and hamstring strain. However, it is unclear whether a high torque ratio of the knee joint flexor muscles to the extensor muscles is beneficial for sport performance. Therefore, the aim of the study was to investigate the relationship between the hamstring-to-quadriceps (H/Q) ratio and sprint times (10- and 30-m) and jump heights (CMJ—countermovement jump and SJ—squat jump) in soccer players. The study examined 26 young elite soccer players (age: 18.1 ± 0.7 years; body height: 1.77 ± 0.05 m; body mass: 72.7 ± 5.7 kg). Knee joint flexor and extensor peak torques were assessed using the Cybex dynamometer (at 60°/s, 120°/s and 180°/s). Additionally, each participant performed the CMJ, SJ, and 30 m sprint. A significant relationship was obtained between the H/Q ratio (60°/s) and 30 m sprint time (r = 0.47). The positive direction of this relationship may indicate an important role of knee joint extensors in sprinting performance. Moreover, the H/Q ratio was not significantly associated with the CMJ, SJ or 10 m sprint performance. The H/Q ratio should be considered together with the peak torque values in terms of the assessment of sprinting and jumping performance.

The relationships between knee extensors/ flexors strength and balance control in elite male soccer players

Background

Strength and balance are important factors for soccer players to be successful. This study’s aim was to determine the relationship between lower-limb muscle strength and balance control in elite male soccer players (n = 77).

Methods

Concentric isokinetic strength (peak torque of quadriceps (PT-Q) and hamstrings (PT-H), hamstrings/quadriceps (H/Q) ratio) was measured for the dominant and non-dominant leg at angular velocities of 60°s⁻¹and 240°s⁻¹, as well as the total work for extensors (TW-Q) and flexors (TW-H) for both legs (at an angular velocity of 240°s⁻¹only). Balance score (BAL score) was used for unilateral assessment of balance control using a Delos Postural System Test measurement tool. Hierarchical multiple regression analyses were performed to predict balance control using isokinetic knee strength performance for dominant and non-dominant legs.

Results

Final modelling included peak torque of hamstrings at 240°s⁻¹ and peak torque of the quadriceps at 240°s⁻¹ for the non-dominant leg (R² = 19.6%; p ≤ 0.001) and only peak hamstring torque at 240°s⁻¹ for the dominant leg (R² = 11.3%; p = 0.003) as significant predictors of balance score.

Conclusion

Findings indicate that balance control is widely influenced by peak hamstring torque and peak quadriceps torque at high angular velocity particularly in the non-dominant leg i.e., the supporting leg in soccer players.