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The Relationship Between Anatomical and Functional Cross-Sectional Area and Isometric Strength in Older Adults: 3192 Board #3 May 30, 9

The age-related reduction in muscular strength occurs at a greater rate than the loss of muscle mass, suggesting a decline in muscle quality (i.e. infiltration of fat and/or connective tissue). Recent magnetic resonance imaging studies have determined functional cross-sectional area (FCSA) measures using grey-scale threshold segmentation to estimate the amount of contractile tissue. These measures may be more closely related to strength and performance than traditional anatomical CSA measures and may be a promising approach with ultrasound (US) imaging. PURPOSE: The aim of this study was to examine the relationship between medial gastrocnemius (MG) anatomical CSA and FCSA with isometric plantar flexion strength. METHODS: Twenty older (age = 69±3 years) males performed two maximal isometric contractions on a calibrated isokinetic dynamometer to determine plantar flexor strength. Peak torque (PT) was calculated as the highest 500ms value. Panoramic B-mode ultrasound images of the MG were taken to determine anatomical CSA. The US images were taken with the participants lying in a prone position with their right leg fully extended and foot secured to vertical post at an ankle joint angle of 90°. The US probe was positioned perpendicular to the skin and moved along the transverse plane of the MG with transmission gel applied to the skin to enhance acoustic coupling. Image-J software was used to determine MG CSA without including any surrounding fascia. Using the same region of interest, FCSA was determined with a minimum and maximum echo intensity threshold for contractile tissue at 0 and 60, respectively. The relationships between isometric PT and both anatomical CSA and FCSA were assessed using Pearson’s correlation coefficients (r) with an alpha level set a priori at P ≤0.05. RESULTS: There was a moderate but non-significant relationship between PT and (r =0.439, P =0.053). However, there was a significant positive relationship between PT and FCSA (r =0.568, P ≤0.01). CONCLUSION: These findings indicate that muscle FCSA is related to isometric PT and may be a better predictor of muscular strength than traditional anatomical CSA measures in older adults.