The figure shows that passive parallel stiffness (i.e., modulus of elasticity) is not different between control and mdx EDL muscles during early maturation. *Parallel stiffness at age 35 d is less than that of other ages (n = 7, P < 0.05). These data suggest that the absence of dystrophin from the muscle membrane (part of parallel stiffness) does not influence stiffness if the imposed muscle stress is submaximal (e.g., mdx, ~70% of maximal isometric tetanic stress at age 28 d) (¹⁵). Does this hold true at greater stresses when the muscles are contracting? If so, this response could partially explain the ability of 4-wk-old young mdx mice to endurance train. Stress is muscle force divided by cross-sectional area. (Reprinted from Wolff A.V., A.K. Niday, K.A. Voelker, J.A. Call, N.E. Evans, K.P. Granata, and R.W. Grange. Passive mechanical properties of maturing EDL are not affected by lack of dystrophin. Muscle Nerve 34(3):304-312, 2006. Copyright ® 2006 John Wiley & Sons, Inc. Used with permission.)