Heat shock protein (HSP) expression in young and aged muscles. Soleus and Epi muscles from young and aged rats were dissected, clamp frozen, and homogenized. Lysates were analyzed by Western blot for HSP72. Filled bars represent young muscle values, and open bars represent aged muscles values. Values are means ± standard error (SE) for 8–15 muscles per group. *P < 0.05, **P < 0.001. (Reprinted from Gupte AA, Bomhoff GL, Geiger PC. Age-related differences in skeletal muscle insulin signaling: the role of stress kinases and HSP. J. Appl. Physiol. 2008; 105:839–48. Copyright © 2008 The American Physiological Society. Used with permission.)