Shape factor index

Older age is associated with shape factor index in humans (8% greater SFI).

“Older participants exhibited smaller type II fibers (28%) and greater fiber shape irregularity (8% SFI) compared with young.”

Humansolder compared with young womenskeletal musclefemales

Capillary differences with age and muscle fiber type are attenuated by accounting for fiber shape

The FEBS journal·10 Jan 2026