Some responses of the child to exercise

Summary The effects of exercise have been studied intensively in twelve children from 11 to 13 years of age. The study has included determinations of the changes in heart rate and systolic and diastolic pressures, resulting from both moderate and maximal work on the bicycle ergometer, and determinations of the changes in many of the blood components under the two conditions of work. An attempt has also been made to relate these changes to the nutritive status and to the physical capacity of the child. The nutritive status of each child has been established by clinical examination, by the weight and fat indices of McCloy, and by creatinine indices. Physical capacity has been measured by performance on the bicycle ergometer. With the exception of serum pH and sodium during moderate work and diastolic pressure, blood sugar, serum chloride, and CO2 tension during maximal work, all of the factors measured showed significant changes as the result of exercise. Pulse rate and systolic pressure increased with exercise, but as work was changed from a moderate to a maximal character little further increase occurred, as a rule. Diastolic pressure showed great variability of response under either condition of work, decreasing in the majority of children during moderate exercise, but showing an increased tendency to rise during maximal exercise. Hemoglobin, red cell volume, and serum protein increased with both moderate and maximal exercise. With one exception (R. W.), the magnitude of the rise was greater during maximal exercise, the maximum increase for an individual child reaching 8.2 per cent for protein, 8.6 per cent for cell volume, and 10.4 per cent for hemoglobin. The sodium and chloride concentration of the serum showed little change, although an increase of approximately 0.7 meq. in chloride during moderate exercise appears to be significant. Serum phosphate increased during both moderate and maximal exercise by a small amount not exceeding 0.3 meq. The rise in phosphate tended to be higher during maximal work. Blood sugar showed small variable responses to exercise but increased slightly in the majority of persons. Serum lactate increased, on the average, by 3.5 meq. during moderate exercise, and by 7.8 meq. during maximal exercise. Serum bicarbonate, corrected to initial pH, showed a corresponding, but slightly greater, fall. The pH did not change appreciably during moderate exercise but decreased on the average, by 0.09 during maximal work. Greater variations in response occurred during moderate work in pulse rate and serum lactate, bicarbonate, CO2 tension, sugar, and phosphate, and during maximal work in systolic, diastolic and pulse pressures. These factors would, therefore, appear to offer more fruitful fields for investigation of individual differences and their relation to physical capacity. The present investigation was limited to too small a number of children and too heterogenous a group to enable us to draw conclusions, but a few relationships appear suggestive. Superior physical capacity is indicated in the child, as well as in the adult, by the lack of a significant rise in serum lactic acid and a corresponding fall in bicarbonate when a fixed moderate task is performed. Those children showing the smaller, often insignificant, rises in phosphate during moderate exercise possess good or superior physical capacity. These children also show little change or a slight fall in blood sugar under such conditions while the others exhibit a rise which may become marked. The children showing the higher cardiovascular responses to moderate work are only fair or poor in physical capacity. While nutritive status undoubtedly has some effect upon the physical response of the child, many other factors complicate the problem. Many more children will have to be studied and the various factors interrelated in some statistical manner before much progress can be made in the solution of the problem. We feel, however, that the methods used in the present investigation offer valuable tools for its solution.