Hallmarks of cellular senescence in skeletal muscle. p16 and p21 gene expression in quadriceps (quad), gastrocnemius (gas), tibialis anterior (TA), soleus (sol), and extensor digitorum longus (EDL) muscles of (a) young (6-mo, n = 8) and old male mice (24-mo, n = 11) and (b) young (n = 5) and old female mice (n = 5; Two-tailed unpaired t tests). (c) Heatmap of senescence-related gene expression in quad muscle from young and old mice (female, young n=9, old n=10; Two-tailed unpaired t tests). Staining (d) and quantification (e) of telomere-associated DNA damage foci (TAF), senescence-associated distension of satellites (SADS), Lamin B1, and high-mobility group box protein 1 (HMGB1) in quadriceps muscle cross-sections of young (n = 6) and old (n = 5) male mice (Two-tailed unpaired t tests). Error bars represent the standard error of the mean. *, **, and *** denote p < 0.05, 0.01, and 0.001 respectively.