Muscle Architecture Symmetry and Functional Performance in Healthy Young Adults Assessed by Ultrasonography and Field Tests: Cross-Sectional Study

Objective: To compare muscle architecture, ankle strength, joint mobility, and functional performance between dominant and non-dominant lower limbs in healthy young adults, and to examine associations between ultrasonographic architecture and field-based functional tests. Material and Methods: Twenty-four (11 males, 13 females; mean age: 24.1±2.1 years) healthy adults underwent bilateral ultrasound of medial/lateral gastrocnemius, tibialis anterior, and Achilles tendon to assess muscle thickness, pennation angle, and fascicle length. Ankle strength was tested via handheld dynamometry. Functional performance included heel-rise height and repetitions, lunge, hop, and jump tests. Wilcoxon signed-rank test and Spearman correlations (r) with r² were calculated. Results: No significant side-to-side differences were found (all p>0.05). In the dominant limb, medial gastrocnemius thickness correlated with dorsiflexor strength (r=0.642, p<0.001) and heel-rise repetitions (r=0.448, p=0.047); medial gastrocnemius pennation angle related to dorsiflexor strength (r=0.463, p=0.023) and endurance (r=0.556, p=0.011). Tibialis anterior pennation angle was linked to vertical jump (r=0.567, p=0.004) and heel-rise height (r=0.549, p=0.005). Achilles thickness correlated with jump (r=0.572, p=0.003). In the non-dominant limb, tibialis anterior thickness correlated with repetitions (r=0.607, p=0.005) and single-leg hop (r=0.436, p=0.033); lateral gastrocnemius pennation angle was inversely related to plantarflexor strength (r=-0.455, p=0.025). Conclusion: Despite symmetry, muscle thickness and pennation angle showed moderate correlations with function, supporting their clinical relevance.