RESUMEN
BACKGROUND & AIMS: Ultrasound can be used to measure the pennation angle between muscle fiver and the presumed axis of force generation and muscle echogenicity as an indicator of muscle fat infiltration. We aimed to assess the association of the rectus femoris pennation angle and echogenicity with muscle functional measures. Also, to assess the concordance of rectus femoris echogenicity with muscle fat infiltration as determined by CT scan. METHODS: Rectus femoris ultrasound pennation angle and thickness were measured in 78 participants aged 69 (65,73) years (37 women). Also hand grip strength, gait speed in 4 m, the 12 min' walk and body composition by DEXA were measured. In a different group of 114 participants aged 44 (31,52) years (80 females), non-dominant rectus femoris echogenicity and thickness were measured by ultrasound and muscle fat infiltration was assessed by CT scan. Handgrip strength and quadriceps torque were also measured. RESULTS: There was a weak correlation between the pennation angle and rectus femoris thickness in men (r = 0.31 p = 0.05) but not in women (r = 0.29 NS). Women, but not men with a low pennation angle covered a longer distance during the 12 min' walk. The concordance between the z scores of rectus femoris echogenicity and CT radiological density was 0.43 (p < 0.01) and 0.01 (NS) in men and women, respectively. Men and women with an echogenicity below the 25th percentile had a higher quadriceps torque. Men with an echogenicity 25th percentile below 25th percentile had also a higher handgrip strength. CONCLUSIONS: Rectus femoris pennation angle had a weak or absent association with muscle performance. Rectus femoris echogenicity had a moderate overall concordance with radiological density by CT scan and was inversely associated with quadriceps torque. Therefore, echogenicity was associated with muscle strength, but pennation angle measurement did not contribute to the assessment of muscle function.
