The objectives of the present study were to find out peculiar cardiorespiratory adjustments of young children against relatively short duration of exhaustive run.
Young four male and four female children, aged four or five years, ran on the flat treadmill firstly with the velocity where they could continue to run at least for five minutes (140m/min for male children and 120m/min for female children) and thereafter with three different kinds of velocities where they were forced to cease running because of their exhaustion (160, 180 and 200m/min for male children and 140, 160 and 180m/min for female children) .
Increase rates and recovery rates converted from absolute values of of HR (bpm) and Vo₂ (1/min) in each phase were used for analysis.
The results obtained were as follows;
1) Also for young children changes of increase rates and recovery rates of HR and Vo₂ to the time course showed the exponential inclinations.
2) Fifteen seconds after the commencement of running the increase rates of HR ranged from 56.0 to 65.0% and those of Vo₂ ranged from 42.5 to 53.3% for male children and on the other hand for female children ranged from 49.0 to 58.2% and 38.9 to 43.5% respectively.
The increase rates of HR were, therefore, steeper than those of Vo₂ for both sexes.
Significant differences were found in the velocities of 160, 180 and 200m/min for male children and 140 and 180m/min for female children.
3) The increase rates of HR attained fifteen minutes after the start of running corresponded to one the second or two the third of 82.0 to 91.0% and 81.6 to 87.3% which were attained one minute after the start of running for male and female children respectively.
4) In spite of the absolutely and relatively greater range of adjustment, which means the larger difference between values at rest and maximal effort, the increase rates of Vo₂ reached or surpassed those of HR one minute after the start of running.
5) The ranges of adjustment of HR and Vo₂ were higher for male children, but the both increase rates exhibited till one minute after the start of running, though no significant differences were found, were higher for male children.
6) On the contrary to the case of increase rates the recovery rates of Vo₂ were significantly higher than those of HR at least till two minutes after the cessation of running for both sexes.
Vo₂ returned to the level of rest only five minutes after the cessation of running, but HR lied a little higher above the resting level even fifteen minutes later.
7) The higher acceleration of increase rate and deceleration of recovery rate for young children are presumably much due to the smaller range of adjustment. Accordingly the experiments sould be designed by unifying exhaustion time.