Lower limb muscle strength, inter-limb asymmetry, and vertical jump performance in elite female football players: A cross-sectional study

Abstract

Lower limb strength imbalance and inter-limb asymmetry are relevant neuromuscular screening markers in women’s football, yet data from national-champion squads in Eastern Europe remain limited. The aim of this study was to characterise lower limb isometric knee strength, hamstring-to-quadriceps (H:Q) ratios, and bilateral and unilateral squat jump (SJ) and countermovement jump (CMJ) performance, and to describe their distribution by playing position, in elite Bulgarian female football players. Nineteen players from FC NSA Sofia Women (Bulgarian Women’s Football Champions, 2024/25; age 20.9 ± 4.3 years; height 168.4 ± 4.7 cm; body mass 60.5 ± 8.0 kg; body mass index 21.3 ± 2.7 kg·m −2 ) were assessed on a single testing day using a handheld dynamometer (Kineo Intelligent Load) and an optical jump system (Optojump Next). Mean H:Q ratios were 0.58 ± 0.10 (left, 95% CI [0.52, 0.64]) and 0.55 ± 0.07 (right, 95% CI [0.51, 0.60]); the right-limb mean was statistically below the 0.60 reference threshold (t(13) = −2.40, p = 0.032, d = −0.64). Thirteen of fourteen assessed players (92.9%, 95% CI [68.5–98.7%]) presented at least one limb with an H:Q ratio below 0.60. Mean bilateral SJ and CMJ were both 29.2 cm, producing a near-zero elasticity index (0.99 ± 10.6%). Unilateral asymmetry exceeding 10% was observed in 52.9% of players for SJ (95% CI [31.0–73.8%]) and 35.3% for CMJ (95% CI [17.3–58.7%]). Positional profiles are reported descriptively only, given the small subgroup sizes. The findings support routine neuromuscular screening of lower limb strength balance and unilateral jump performance in elite women’s football, and indicate that conditioning programmes should address both hamstring and quadriceps capacity rather than hamstring strength in isolation.