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Few data exist identifying the influence of age on midthigh muscle composition. Further understanding how muscle composition of the midthigh changes with aging may improve current exercise prescriptions. PURPOSE: To examine the influence of chronological age on midthigh composition in 142 women (49.1±17.7 years, 164.5±7.1 cm, 66.6±10.7 kg). METHODS: Midthigh peripheral quantitative computed tomography scans were completed at the 40% site of the right femur and were analyzed using BoneJ software. Muscle density (MuD), cross-sectional area (mCSA), and intramuscular fat area (IMAT) were derived from the scans. One-way ANOVA compared group means by decade 20-29 (n=28), 30-39 (n=21), 40-49 (n=22), 50-59 (n=25), 60-69 (n=29), ≥70 years (n=17), while Dunnett's test performed post-hoc pairwise comparisons with the youngest group. Spearman's correlations examined each parameters association with age. A significance level of p<0.05 was selected a priori. RESULTS: MuD and mCSA displayed significant negative associations with age (r=-0.58 and r=-0.67, respectively, both p<0.01), while IMAT displayed a significant positive association with age (r=0.17, p=0.04). Group differences were observed for MuD (p<0.01), mCSA (p<0.01), IMAT (p=0.029). Dunnett's test revealed that MuD was significantly greater in the 20-29 years group compared to both age groups ≥60 years (81.5±1.2mg/cm³ vs 79.1±2.2mg/cm³ and 78.2±2.9mg/cm³, respectively; both p<0.01), and mCSA was significantly greater in the 20-29 years group compared to each age group ≥50 years (104.4±15.4cm² vs 85.9±14.3cm², 78.8±12.4cm², and 72.3±14.5cm², respectively, all p<0.01). IMAT was significantly greater in ≥70 years group compared to the 20-29 years group (6.23±2.3cm² vs 4.3±1.8cm², p=0.04). Interestingly, MuD, a surrogate for muscle quality, displayed smaller age-related decreases than mCSA (MuD: -3.9% vs mCSA: -29.7%) between the 20-29 and ≥70 years group. CONCLUSIONS: The current observations reveal that increased age displayed significant associations with midthigh muscle composition (MuD, mCSA, IMAT). However, future research is needed to identify which muscle composition parameter(s) contribute most effectively to maintaining muscle strength and physical performance with advanced age. [ABSTRACT FROM AUTHOR]