Sept 4, 1967

Anatomical and Biochemical Adaptations of Muscle to Different Exercises

Author Affiliations

From the Division of Physical Medicine and Rehabilitation, Department of Medicine, Michael Reese Hospital and Medical Center, Chicago.

JAMA. 1967;201(10):755-758. doi:10.1001/jama.1967.03130100053013

"Work-hypertrophy" is a universally accepted concept of physiology. It implies that all effort leads to muscle enlargement and, by the same token, hypertrophy always accompanies increased ability for muscular performance. This implication is generally true, but understanding of the process may need modification.

First, what is meant by hypertrophy: increase in girth of a limb, volume of a muscle, or the related weight? Or, are we referring to the individual muscle fiber, the smallest anatomical unit of muscle? In work-hypertrophy, the gross and microscopic dimensions are regarded as running parallel courses and, therefore, as being interchangeable. There would be no serious error if in hypertrophy the sum of the enlarged parts equalled an increased whole. But such an equation is not always found. Consequently, human experiments relying on gross dimension such as girth as an index of hypertrophy may fail to reveal the true state of affairs.

Furthermore, in the