Contractile and non-contractile tissue volume and distribution in ankle muscles of young and older adults

► We used MRI to examine ankle muscle volume and distribution in young and older adults. ► Older adults had a greater proportion of non-contractile tissue compared to young. ► The proportion of non-contractile tissue was smallest near the muscle belly centers. ► A mathematical model predicted muscle volumes with 8-11% error using one MRI slice. ► Use of multiple slices increased volume prediction accuracy; error decreased to 3-4%.