Morphological and Mechanical Symmetry of the Quadriceps and Hamstrings in Athletes

Sports performance can be influenced by several multifactorial conditions. Symmetries between sides can interfere with muscle strength, impacting performance. Balance in morphological aspects and muscle strength is desirable between dominant (DO) and non-dominant (ND) lower limbs to improve performance or to prevent injuries. The study aimed to compare quadriceps and hamstring muscle morphology and knee extensor and flexor torque while analyzing whether cross-sectional area (CSA) and echo intensity (EI) can better explain maximal concentric torque in competitive athletes. Sixteen competitive athletes of team sports were evaluated. Quadriceps and hamstring CSA and EI were assessed using a B-mode ultrasound. The maximal torque production capacity of the quadriceps and hamstrings was evaluated using an isokinetic dynamometer protocol. Our backward multiple linear regression models indicated that the quadriceps cross-sectional area (CSA) and echo intensity (EI) of the dominant (DO) and non-dominant (ND) limbs explain 61–79% of concentric torque production at 60°/s and 300°/s, with CSA showing a positive relationship and EI a negative one. Likewise, hamstrings CSA and EI account for 70–77% of torque production at the same angular velocities, both exhibiting positive relationships with torque output. Our data present bilateral mechanical and morphological symmetries in lower limbs of amateur athletes and potential predictive concentric torque capacity of CSA and EI for quadriceps and hamstrings.