Purpose The purpose of this study was to assess if differences in hamstring strength, hamstring-to-quadriceps (H:Q) strength ratio, and biceps femoris long head (BFLH) fascicle length exist between male and female professional football (soccer) players. Methods One-hundred professional footballers participated in this cross-sectional study: 50 men and 50 women. Ultrasound images of BFLH muscle and isokinetic dynamometry tests were performed. Results Men were stronger than women for hamstring concentric (2.01 ± 0.21 Nm/kg vs. 1.55 ± 0.23 Nm/kg; p < 0.001; large effect size, 2.08) and eccentric (2.87 ± 0.45 Nm/kg vs. 2.39 ± 0.32 Nm/kg; p < 0.001; large effect size, 1.23) peak torques. There was no sex-related difference for H:Q conventional ratio (concentric/concentric; 0.55 ± 0.06 vs. 0.55 ± 0.07); but women presented greater H:Q functional ratio (eccentric/concentric; 0.78 ± 0.12 vs. 0.85 ± 0.09; p = 0.003; moderate effect size, 0.66). Men and women presented similar BFLH fascicle length: 0.24 ± 0.05 vs. 0.23 ± 0.05 (values normalized by muscle length). Conclusions Among the muscular factors assessed in this study, men presented stronger hamstring muscles, women presented greater H:Q functional ratio, and there was no sex-related differences for H:Q conventional ratio or BFLH fascicle length.
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