The aim of the present investigation was to contribute to the physiological understanding of the great physical performances made, for instance, in sport, games, and physical education activities. During heavy prolonged work, the supply of oxygen may be considered as a limiting factor. Consequently, in this investigation special interest was payed to determining the maximal oxygen intake and related metabolic and heart rate measurements of boys and girls between ages of six and twelve and to identifying any existing physiological differences among the sexes and the various age groups. The maximal oxygen intake was determined during their performance of a progressively loaded, step increment test on a bicycle ergometer. The results of this investigation were as follows: 1. The mean values of maximal heart rate ranged 190-200 beats/min, where no sex and age differences were found. 2. As for the maximal respiratory rate no sex difference was found, but it showed gradual decrease with age from ten to twelve years. 3. As for the maximal oxygen intake, it increased with age without distinction of sex, but girls showed lower values than boys in every age group. 4. The maximal oxygen intake per kilogram of body weight decreased with age up to nine years, then, increased slightly, and showed constant value. But, girls showed lower values than boys in every age group. As compared with Åstrand's and Wilmore's data, the results of this investigation showed lower values. (about 10-20 ml/kg/min) 5. As for the maximal ventilation, it changed with age in the same manner as the maximal oxygen intake. But, the tidal volume increased rapidly with age from ten to twelve years, and girls showed lower values than boys in every age group.
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