Side-to-side asymmetry in lower limb strength and hamstring-quadriceps strength ratio among collegiate American football players

[Purpose] The present study aimed to investigate the lower limbs injury risk factors that are based on conventional Hamstring to Quadriceps ratio and limb asymmetry index in varsity American football players. [Participants and Methods] Twenty-six varsity American football players aged 19–27 years and with 2.31 ± 1.29 years of American football experience from Dogu Akdeniz University volunteered to undergo measurements of average peak torque for isokinetic flexion and extension of dominant limb and non-dominant limb at 60°·s(−1) and 300°·s(−1). Hamstring to Quadriceps ratio and limb asymmetry index were also calculated for Hamstring and Quadriceps muscles. [Results] Statistical analysis revealed that dominant Quadriceps is stronger than non-dominant Quadriceps at 60°·s(−1) speed. No statistical difference was found between dominant and non-dominant Hamstring peak torque at 60°·s(−1) . Hamstring to Quadriceps ratio determined as normal both for 60°·s(−1) and 300°·s(−1)according to the currently reported cut off value (H:Q ratio >60). Hamstring and Quadriceps limb asymmetry index also determined as normal (cut off value for LSI 10%) at 60°·s(−1). However, for both Hamstring and Quadriceps, side- to- side strength asymmetry at 300°·s(−1) was observed. [Conclusion] To prevent possible lower limb injury and to increase performance, varsity American football players who are actively training and competing might consider taking strength asymmetry into account to tailor their strength training program accordingly.