Cross-sections of the gastrocnemius (a-h) and soleus (i-p) muscles were stained with HE. Arrowheads indicate spikes and lakes in cytoplasm (e-h). Scale bar = 50 μm. GAS, gastrocnemius muscle; SOL, soleus muscle; 3M, 3-month-old mice; 24M, 24-month-old mice.</p