Severe exercise not only involves a good many muscles, but causes enough strain to harden and enlarge them. Bicycling up grade, swimming, and other active sports would be included in this kind of exercise. Lumbermen, excavators, and a few others do even heavier work than this. Knowing the weight of a grown man or woman, and something of the daily occupation, as in the case of a professional man, we can estimate the probable energy requirement somewhat as follows: Sleeping, 8 hours; 8 × 0.4 Calories = 3.2 Calories per pound. Sitting quietly (at meals, reading, etc.), 8 hours; 8 × 0.6 Calories = 4.8 per pound. At light muscular exercise (dressing, standing, walking, etc.), 6 × 1.0 Calories = 6.0 Calories per pound. At active muscular exercise 2 hours, 2 × 2.0 Calories = 4 Calories per pound. Total Calories per pound for 24 hours, 18; 18 × 154 pounds (the weight of the average man) = 2772, or approximately 2680, Calories per day required. Calculate in this way the energy requirement for various grown persons whom you know. =Energy requirements during growth.=——In estimating food requirements of those who are under twenty-five years old, we must bear in mind that the same materials which serve for fuel serve in part for building material. Protein is used for muscle building as well as for supplying energy, and the larger one grows, the greater the reserves of carbohydrate and fat which he can carry. Furthermore, internal activity is greater in the young than the middle aged or very old, and external activity is apt also to be greater. Think, for instance, how much running children do compared with their parents. For all these reasons, we cannot use the table for adults in calculating the energy requirement of young people. In the following table an attempt has been made to take account of their greater needs, but the estimates include only moderate exercise; with hard work more will be required. Notice that the highest allowance per pound of body weight is for the youngest children. ENERGY REQUIREMENTS DURING GROWTH Age in Years Calories per pound per day Under 1 45 1-2 45-40 2-5 40-36 6-9 36-30 10-13 30-27 14-17 27-20 17-25 not less than 18 With these two tables for calculating energy requirement we can determine about how much will be needed by each member of the family. A group consisting of a professional man, his wife, and three children under 16 will require about 10,000 Calories per day; a workingman’s family with the same number of children from 12,000 to 14,000, because of the harder work which both parents and possibly the children will do.