Document Type



Calculations of total body water, lean body weight and fat were made at menarche and at initiation of the adolescent growth spurt for each of 181 girls from height and weight of each girl at each event; the changes in these components were found for each of 169 girls. At menarche, mean total water is 26.2 ± 0.18 liters, mean fat is 11.5 ± 0.29 kg; early and late maturing girls do not differ in total water. Mean total water/body weight percent decreases from 60.4 ± 0.28 at spurt initiation to 55.1 ± 0.27 at menarche. The coefficient of variability of total water/body weight at menarche is 55% less than that of weight at menarche. During the interval from spurt initiation to menarche, both early and late maturing girls gain an average of 7.6 liters of body water, 10.7 kg of lean body weight, a 42% increase, and 6.4 kg of fat, a 125% increase, resulting in a change of ratio of fat/lean body weight from 1:5 at spurt initiation to 1:3 at menarche. At menarche, and at spurt initia­tion, early maturers have a greater increase of fat per kilogram increase of lean body weight than do late maturers. The reductions in variability when weight at menarche is converted to total water and total water/body weight percent, and the body composition changes are in accord with the hypothesis that a critical metabolic rate triggers menarche. Of 169 girls, 138 (82%) remain in the same quartiles of total water/body weight from initiation of the spurt to menarche compared to only 79 (47%) remaining in the same quartiles of weight from initiation to menarche.