Quantitative Muscle Fiber Analysis

All sections were imaged using a Zeiss Axio Imager microscope at ×20 magnification. Images were tiled using Zen software. Fiber CSA was quantified on whole muscle cross sections using Myovision analysis software (45 (link), 46 (link)). eMyHC⁺ muscle fibers were quantified on whole muscle cross sections by a trained and blinded technician. Central nucleation was quantified on whole muscle cross sections using MuscleJ analysis software (47 (link)). γH2AX⁺ and p21⁺ nuclei were quantified from representative regions of interest (ROIs) using Myovision analysis software. Fibrosis was quantified with ImageJ software (NIH) using representative regions of interest from Masson’s trichrome–stained sections, as described previously (46 (link)).