In this age of mental development, when the achievement of success can come only through the exercise of the mental capacities, we are apt to forget the maxim "mens sana in corpore sano" and allow the balance between mind and body to be broken. To be sure, the material return in occupations requiring the use of the muscles alone cannot ever equal the return from occupations requiring the exercise of the mind—if we are to measure success by return—nevertheless, the sphere of one's usefulness with a poorly developed body is necessarily limited and short-lived. Civilization unquestionably tends toward an overdevelopment of the mind at the expense of the body. Recently, and in recognition of the marked muscular deterioration of the civilized races, the necessity for improving their development has received much attention.
The term "physical development" applies mainly to muscular development. A short muscular individual could
FRIEDMAN HM. MUSCULAR DEVELOPMENT, THE CAUSES FOR THE LACK OF IT AND THE VALUE OF PHYSICAL EXERCISE. JAMA. 1912;LVIII(10):685-689. doi:10.1001/jama.1912.04260030085004