Association between temporal muscle morphology based on MRI and muscle mass and strength in healthy young adults: a cross-sectional study.

BACKGROUND: Temporal muscle morphology, easily visible on cranial magnetic resonance imaging (MRI), is increasingly recognized as a noninvasive biomarker of systemic muscle health. This study examines the association between temporal muscle thickness (TMT) and temporal muscle area (TMA) with skeletal muscle mass, strength, and physical performance in healthy young adults. METHODS: This prospective cross-sectional study involved 61 healthy adults (29 men and 32 women; mean age: 21.7 ± 5.4 years). Participants underwent high-resolution 3T cranial and lumbar magnetic resonance imaging (MRI) between September and October 2025. TMT, TMA and lumbar skeletal muscle cross-sectional area at the third lumbar vertebra (L3-CSA) were systematically quantified. In addition, grip strength, gait speed, and anthropometric measurements were assessed to evaluate functional and morphological aspects of muscle condition. Correlations between temporal muscle parameters and systemic muscle indices were analyzed using Spearman’s rank correlation and Bonferroni correction for multiple comparisons. Partial correlations controlling for sex and BMI and formal sex interaction tests were also performed. Group comparisons were conducted using independent t-tests or Mann–Whitney U tests. RESULTS: The mean TMT was 7.6 ± 1.1 mm, whereas the mean TMA was 5.3 ± 1.4 cm². TMA demonstrated strong correlations with L3-CSA (r = 0.69, 95% CI = 0.52–0.81, p < 0.001, corrected p < 0.001), grip strength (r = 0.60, 95% CI = 0.39–0.75, p < 0.001, corrected p < 0.001), and waist circumference (r = 0.61, 95% CI = 0.40–0.76, p < 0.001, corrected p < 0.001). TMT showed moderate correlations with these same parameters: L3-CSA (r = 0.45, 95% CI = 0.22–0.63, p < 0.001, corrected p < 0.05); grip strength (r = 0.41, 95% CI = 0.18–0.60 p < 0.001, corrected p < 0.05), and waist circumference (r = 0.38, 95% CI = 0.18–0.60, p < 0.001, corrected p < 0.05). Neither TMT nor TMA correlated with gait speed or calf circumference. After partial correlation analyses that controlled sex and BMI, the correlations were substantially attenuated and none remained statistically significant. Sex-specific analyses revealed that men had significantly greater TMT and TMA compared to women (both p < 0.001). In multivariable linear regression models adjusting for BMI, a significant sex interaction was observed for the relationship between TMT and psoas muscle area (β = 0.79, 95% CI = 0.10–1.48, p for interaction = 0.025), indicating a stronger association in males. No other significant sex interactions were detected (all p > 0.05). CONCLUSIONS: In healthy young adults, MRI-derived TMT and, in particular, TMA are associated with key indicators of muscle mass and strength. TMT and TMA reflect global physiological status rather than serving as an independent functional indicator in this age group. TMA emerged as the more robust metric, warranting its prioritization in future research. Further validation in older adults and clinical populations with functional decline is essential to establish its clinical utility.