# Influence of Knee Angle on Hametring/Quadriceps Strength Ratio in Male Soccer Players  
[PERSON]  
1 San Juan de Dros Foundation, 28016 Madrid, Spain; [EMAIL_ADDRESS] (N.P.M.);  
[EMAIL_ADDRESS] (M.J.M.B.); kcuellar@comillas.  
the hamstering must contract very rapidly (\(<\)250 ms) to decelerate the inertia [15]. We know that 80% of hamstring injuries occur in the biceps femoris, specifically in their long portion [9], possibly due to structural factors, and kinematic factors of running [16].  
There are several non-modifiable risk factors that may increase the risk of hamstring injury: previous anterior cruciate ligament or hamstring injuries, age, weight, gender or race [17] and a previous hamstring injury [18; 19]. Other modifiable risk factors include a deficit in hamstring or quadriceps muscle strength [4; 19], decreased hamstring flexibility [20; 21], gluteal muscle inhibition [22; 23], increased biceps femoris/semicontinosus muscle activation ratio [24], muscle fatigue [25], and decreased hamstring/quadriceps (H/Q) strength ratio below 0.47 [26]. However, some authors state that these data only predict 2.7% of injuries [27]. [PERSON] et al. [28] found that the angle at which the maximum peak strength of the hamstring musculature was produced can be a predictive factor of hamstring injuries. Notably, the maximum peak strength of the hamstring musculature is optimal the closer it is to 0\({}^{\circ}\) of knee flexion [29]. Considering that the hamstring musculature reaches its maximum peak strength at approximately 30\({}^{\circ}\) of knee flexion (in healthy subjects) [28], hamstring injuries almost always occur with the knee in extension [9], the current measurement of the H/Q strength ratio may not be entirely accurate in predicting hamstring injuries, and these tests should be performed under more game-like circumstances [3].  
In the measurement of knee strength, the angle where maximum torque occurs is not the same for quadriceps (\(\approx\)70\({}^{\circ}\) concentric) as for hamstrings (\(\approx\)60\({}^{\circ}\) concentric and \(\approx\)30\({}^{\circ}\) eccentric) as shown in the study by [PERSON] et al. [30]. The maximum torque depends, in part, on the lever arm, depending on the muscle length that varies depending on the joint range. In the anterior and posterior thigh muscles, the H/Q ratio may be reduced in clinical relevance for this reason [31] because when quantified at different joint angles, they cannot determine the co-contraction capacity of these muscles [32]. To solve this problem, measurements of the H/Q ratio can be made at specific knee flexion angles to improve athlete evaluation data specificity and sensitivity. Studying these new H/Q ratios with an emphasis on angles close to knee extension, where most hamstring injuries occur, can help reduce the total number injuries since specific strength protocols can be performed at knee angles where deficits have been found [31] since it has been seen that strength training at specific angles improves strength at that angle [30].  
Therefore, the present study evaluated different H/Q ratios in male soccer players at various knee flexion angles and analyzed differences with the conventional ratio that could be used to improve the prediction of hamstring injuries.