Muscle Volume And Fat Fraction In Low Active Young And Older Females

Older adults display age-related deficits in ankle kinematics and kinetics for reasons that are poorly understood. Reductions in the ankle plantarflexor (PF) muscle function due to loss of muscle volume (MV) or increase in intramuscular fat content (FF%) may contribute to the changes in ankle mechanics. Prior work has reported that older adults display decreased MV and increased non-contractile content of the PF, while others have reported no change in MV and an increase in FF%. These conflicting findings may be due to differences in the magnetic resonance imaging approaches used or the physical activity level of the participants. PURPOSE: 1. To quantify and compare MV and FF% estimates using 6 mm vs. 12 mm slice thickness (ST) of the dorsiflexors (DF) and PF muscles. 2. To test for age differences in MV & FF% of the DF and PF muscles for young and older low active females. METHODS: Axial images of the shank were acquired using a 6-point Dixon technique (2 stacks, 6 mm ST, 80 slices, 1.25 x 1.25 x 6 voxel volume) for 2 young (YF; 32.5 ± 3.5 yrs.; 192 MVPA/wk.) and 2 older (OF; 71 yrs.; 252.1 ± 4.1 MVPA/wk.) low active females. The borders of the anterior compartment and each triceps surae muscle were outlined in every slice of the 2 OF. The 6 mm slices were then averaged to get 12 mm slices that were segmented for both OF and YF. Age comparisons were made using Cohen’s d effect sizes. RESULTS: The differences between ST were less than 8% and 5% for MV and FF% respectively. MV for the medial and lateral gastrocnemius was smaller in OF while FF% was higher in the DFs and soleus in OF. CONCLUSION: Small differences in MV and FF% estimates between ST suggest 12 mm slices may be used for reducing extensive analysis time. In partial agreement with prior work MV decreases of the gastrocnemii but not soleus was observed. While MV differences were largest for the medial gastrocnemius the FF% was not impacted by age. The functional consequences of the muscle specific age differences are not clear. NIH R01 AG068102