Extended Abstract
Background and Purpose
Football, as a high-impact and dynamic sport, carries a significant risk of musculoskeletal injuries, with hamstring strains being among the most prevalent. The isokinetic hamstring-to-quadriceps (H/Q) strength ratio is a critical biomechanical and neuromuscular indicator for assessing muscular balance and predicting lower limb injury risk, particularly hamstring injuries. The conventional H/Q ratio (Hcon/Qcon) compares concentric strengths of the agonist and antagonist muscles, while the functional H/Q ratio (Hecc/Qcon) compares the eccentric strength of the hamstrings to the concentric strength of the quadriceps, more closely mimicking the deceleration demands of high-speed running. Structured neuromuscular training programs, such as "Football+," have been developed to mitigate injury risk by enhancing strength, proprioception, and dynamic control. This randomized controlled trial aimed to investigate the specific effects of an eight-week, supervised Football+ (Level 1) program on both the conventional and functional isokinetic H/Q ratios in the lower limbs of young male amateur football players.
Methods
The study employed a randomized controlled trial design. Thirty male amateur football players from Tehran's second-division youth league were randomly allocated into two groups: an experimental group (n = 15) and a control group (n = 15). Participants were matched for age, weight, and height. The experimental group replaced their standard warm-up routine with the Football+ (Level 1) program, performed twice weekly for eight weeks. The control group continued their traditional warm-up protocol, which consisted of running, basic football drills, and static stretching. The Football+ program is an integrated neuromuscular training protocol comprising three parts (running exercises, strength, plyometric, and balance exercises, and advanced running exercises) and is designed with three progressive levels of difficulty. Due to external disruptions (severe air pollution in Tehran leading to cancellations), only Level 1 of the program was implemented throughout the intervention period.
Isokinetic peak torque of the knee flexors (hamstrings) and extensors (quadriceps) was assessed pre- and post-intervention using a Biodex isokinetic dynamometer. Assessments were conducted at angular velocities of 60°/s (slow) and 180°/s (medium) for both the dominant (preferred kicking leg) and non-dominant limbs. Concentric strength for both muscle groups was evaluated using a concentric-concentric (con-con) protocol. Eccentric hamstring strength was also tested using an eccentric-eccentric (ecc-ecc) protocol; however, due to a technical error, eccentric quadriceps data for most participants were not saved, precluding the calculation of a combined H/Q ratio. From the collected data, both the conventional ratio (Hcon/Qcon) and the functional ratio (Hecc/Qcon) were calculated for each limb and velocity.
Statistical analysis was performed using SPSS software. The normality of data distribution was confirmed using the Shapiro–Wilk test. A repeated-measures analysis of variance (ANOVA) was employed to examine within-group (time) and between-group (intervention) effects, as well as time-by-group interactions, with the significance level set at α ≤ 0.05.
Results
The analysis of the eight primary outcome variables (conventional and functional ratios at 60°/s and 180°/s for both the right and left limbs) yielded specific and nuanced findings. The most significant results pertained to the functional H/Q ratio (Hecc/Qcon) in the left limb. For the left limb at 60°/s, while the time-by-group interaction was not significant (F(1,24) = 1.918, p = 0.179), the analysis of between-group effects revealed a statistically significant difference between the Football+ and control groups (F(1,24) = 8.147, p = 0.009), with a large effect size (η² = 0.25). Similarly, for the functional ratio in the left limb at 180°/s, a significant between-group effect was observed (F(1,24) = 12.693, p = 0.002), with an even larger effect size (η² = 0.35).
In contrast, none of the other six variables demonstrated statistically significant differences. This includes the conventional H/Q ratio (Hcon/Qcon) at both 60°/s and 180°/s for both the right and left limbs, and the functional H/Q ratio for the right limb at both testing velocities. All between-group p-values for these variables were greater than 0.05, indicating that the Football+ intervention did not produce a statistically significant effect on these specific parameters under the given conditions.
Conclusion
This study provides preliminary evidence that an eight-week supervised Football+ (Level 1) program can positively influence the functional H/Q ratio, a key biomechanical risk factor for hamstring injuries, particularly in the support limb. This highlights the potential of integrated neuromuscular training, even at a foundational level, to modify injury risk profiles. The specificity of the effects to the functional ratio and the non-dominant limb offers valuable insights for coaches and sports medicine professionals, emphasizing the need for targeted assessment and training. While the program did not significantly alter conventional strength ratios, its implementation as a standard warm-up routine represents a practical and effective strategy within a comprehensive injury prevention framework. Future research should investigate the long-term effects of the full, multi-level Football+ program on actual injury incidence rates in conjunction with detailed biomechanical profiling.
Article Message
The results of this study showed that eight weeks of the Football Plus (Level 1) program can improve the functional ratio of the hamstrings to the quadriceps in amateur football players, which was especially evident in the supporting limb. This improvement in the functional balance of the knee muscles can play an important role in reducing the risk of hamstring injuries and improving the neuromuscular stability of players. Therefore, coaches and training professionals can use this program as a practical and evidence-based method to enhance neuromuscular function and prevent injury in football players.
Ethical Considerations
This study has a research ethics certificate from the Research Ethics Committee of the Institute of Physical Education and Sport Sciences of Tehran, code IR.SSRC.REC.1402.069.
Authors' Contributions
All authors participated in all stages of the research, including study design, data collection, statistical analysis, interpretation of results, and writing the final version of the article, and all confirm the accuracy and authenticity of the data and research findings.
Conflict of Interest
The authors of this article deny any conflict of interest.
Funding
This work is based on research funded by the Iran National Science Foundation (INSF) under project number 4037562.
Acknowledgments
We would like to thank all the participants in this research.