Introduction: Football players are exposed to complex movement tasks such as jumping, changes of direction and speed of movement, and ball striking, which place high demands on the muscles and joints of lower limbs. Therefore, it is important to ensure appropriate development and assessment of muscular performance. The ratio between knee flexors and extensors is one of the key indicators of muscle balance and is commonly used to assess injury risk. Isokinetic dynamometry is considered the gold standard for assessing the muscle performance of major muscle groups. Purpose: The purpose of this literature review was to examine the influence of the muscle performance ratio between knee flexors and extensors on the risk of injury in football players. Methods: We conducted a literature review using the electronic database PubMed. We used the following English keywords and phrases: H/Q ratio, injury risk factor, isokinetic strength imbalance, injury. Results: After applying the inclusion and exclusion criteria, we included six studies in the final analysis. The results of four studies showed a statistically significant lower ratio between knee flexors and extensors and therefore an increased risk of injury, particularly hamstring injuries and the anterior cruciate ligament. Two studies did not find any statistically significant differences. The findings also indicate that the ratio of knee flexors and extensors is influenced by various factors, such as participant characteristics, type of muscle contraction, and angular velocity during testing. Discussion and conclusion: The ratio of knee flexors and extensors is an important indicator of muscular balance, but its predictive value for injury occurrence is not consistent. The findings can serve as a starting point for further research, particularly in the standardization of warm-up and testing protocols, incorporating testing into the pre-competition period and the more consistent use of functional ratios.
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