1. 29 young adult male subjects practiced 15 sec. of maximal isometric contractions of the elbow flexors three times a day, 5 days a week, for 5 weeks. They achieved greater increases in strength than have been claimed for a single two-thirds maximal contraction once a day, although the latter has been said to provide the maximal stimulus for the development of strength. There was a negative correlation between initial strength and strength gains. 2. The correlation between the girth of the upper arm and elbow flexor strength, or between changes in upper arm girth and changes in elbow flexor strength, was insignificant. A significant number of subjects developed positive changes in upper arm girth, although the magnitude of such changes was not significant.