GOLDBERG, ALFRED L. Work-induced growth of skeletal muscle in normal and hypophysectomized rats.‘Am. J. Physiol. 2 13 (5): 1193-l 198. 1967.-These studies were designed to determine whether work-induced growth of muscle requires pituitary growth factors. Compensatory hypertrophy was induced in the rat soleus and plantaris muscles on one limb by cutting the tendons of the synergistic muscle, the gastrocnemius. The contralateral limb received only a sham operation and served as a control. Within a week, the wet weight of the plantaris of the operated limb was 2001, greater and that of the soleus 40% greater than their controls. This response required muscular work. Growth was evident within 24 hr and reached its maximal extent by 5 days. Histological evidence showed that this weight increase was correlated with increased diameters of the muscle cells. The rate and extent of muscle hypertrophy were similar in hypophysectomized and normal animals. These studies support the conclusion that pituitary growth hormone is not essential for skeletal muscle hypertrophy and that two types of muscle growth can be distinguished: I) growth hormone-dependent type, and 2) work-induced hypertrpphy. growth hormone; pituitary; muscle growth; muscular compensatory hypertrophy; developmental growth exercise;