Quantifying thenar muscle biomechanical properties: Sex-based variations and implications for grip strength

Background: Quantifying the biomechanical properties of the thenar muscle can provide valuable insight into hand assessment methods.

Purpose: This study aimed to examine the reliability of myotonometer measurements in determining the biomechanical properties (tone, stiffness and elasticity) of thenar muscles in healthy individuals and explore sex-based variations. Additionally, it assessed the relationship between pinch strength and these properties.

Study design: Cross-sectional reliability study.

Methods: Fifty-five healthy young adult participants were recruited. Biomechanical properties of the abductor pollicis brevis and flexor pollicis brevis muscles - tone (Hz), stiffness (N/m), and elasticity (logarithmic decrement)-were measured using MyotonPRO, while pinch strength was assessed using a Baseline pinch gauge bilaterally. For intrarater reliability, the first rater (R1), conducted two sets of measurements at 30-minute intervals. Inter-rater reliability was evaluated by the second rater (R2) performing a set of measurements between R1's two sets.

Results: Fifty participants [mean age=22.84 (1.01) years, mean body mass index=20.86 (2.82) kg/m²] completed the study. Test-retest reliability for the biomechanical properties of the abductor pollicis brevis and flexor pollicis brevis muscles showed good to excellent consistency (ICCs: 0.78-0.97). Inter-rater reliability demonstrated sufficient consistency across (ICCs: 0.78-0.93). Sex-based differences were observed on the nondominant side, with males exhibiting lower logarithmic decrement scores for both muscles (p<0.05). Negative correlations were found between pinch strength and abductor pollicis brevis logarithmic decrement scores on both sides (p<0.05).

Conclusions: The study confirms the reliability of MyotonPRO in evaluating the mechanical properties of the thenar muscle in healthy subjects, with good to excellent consistency. Sex-based differences in elasticity, along with the positive correlation between pinch strength, underscore the importance of sex-specific considerations, suggesting elasticity may be considered a key factor in grip strength improvement.

Trial registration: ClinicalTrial.gov/NCT06004635.