Six male and seven female children, aged five or six years, ran on the flat treadmill increasing running speeds every two minutes by 20 m/min till their subjective exhaustions. The first steps were started with the speeds of 80 or 100 m/min and the rest periods of 30 seconds were inserted between each successive step for the blood sampling. Expired airs for the determination of oxygen uptakes were collected during the last 30 seconds of every stage. Heart rates were recorded for each subject throughout the whole test session.
Two male and two female subjects were selected in order to determine their physical activity levels in the nursery school. Their heart rates were recorded from Monday to Saturday in a given week.
Analyses of physical activity patterns were tried by relating heart rate levels to circulorespiratory variables which were equivalent to 3 or 4 mmol/l blood lactate concentration (3m MLA or 4m MLA) .
By so doing, the following results were obtained:
1) Mean values of blood lactate concentrations observed immediately after the cessation of the last exhaustive steps were 5.16 m MLA for males and 4.70 m MLA for females.
2) Relative values of heart rate to 3 and 4 m MLA against maximal heart rate (% HRmax-3 m MLA and % HRmax-4 m MLA) were respectively 92.2% HRmax-3 m MLA and 97.5% HRmax-4m MLA for males and 94.9% HRmax-3 m MLA and 98.2% HRmax-4 m MLA for females.
The corresponding relative values of oxygen uptakes were 85.2% Vo₂max-3 m MLA and 94.3% Vo₂max-4 m MLA for males and 89.7% Vo₂max-3 m MLA and 96% Vo₂max-4 m MLA for females.
3) Mean values of heart rate recorded in the nursery through a given week except Sunday ranged from 89 to 114 beats/min for males and 106 to 126 beats/min for females. In the relative value of a heart rate against the heart rate equivalent to 4 m MLA, that is, HR 4 m MLA these values correspond to 44-57% HR 4 m MLA and 57-67% HR 4 m MLA respectively.
4) Accumulated duration time: Their hearts beat higher than 160 beats/min, except in the case of 800 m endurance run (only 0-4 and 0-6 minutes for males and 0-6 and 4-21 (touch of tachycardia) minutes for females) .
Percentages of accumulated duration time lower than 120 beats/min occupied 72-94% and 77-91% of 6 or 7-hour nursing time for males and 51-91% and 51-78% for females.
5) Absolute and relative values of mean heart rates in 800 m endurance run ranged from 183 beats/min (Net 83% HRmax, 90% HR 4 m MLA) to 199 beats/min (Net 98% HRmax, 104% HR 4 m MLA) for males and from 172 beats/min (Net 77% HRmax, 92% HR 4 m MLA) to 196 beats/min (Net 92% HRmax, 96% HR 4 m MLA), though the duration times were short.
6) Optimal intensity of work load was proposed to be the heart rate level of at least 190 beats/min for favourable development and/or improvement of the circulo-respiratory system in young children.

Twelve young boys as an experimental group and seven as a control group, aged 5-6 years, participated in a study to clarify whether circulorespiratory trainability exists in young children. The subjects in the experimental group performed a 915 m endurance run on an agricultural road every day except Sundays for six months. During the run, heart rates (HR) equivalent to 3-4 mmol⋅l^-1 of blood lactate concentration (LA) were maintained for at least 3-4 min⋅m^-1. The control group was given no special training.
Before and after the training period, both groups were subjected to increased stepwise running velocity on a flat treadmill till subjective exhaustion to determine circulorespiratory variables such as heart rate (HR), oxygen uptake (Vo₂) and blood lactate concentration (LA) at all steps.
From the above mentioned procedure, the following findings were obtained :
1) After the 6-month endurance run training, Vo₂max/TBW was significantly (p<0.05) increased from 47.5 to 50.4 ml⋅kg^-1⋅min^-1 and also the peak LA was significantly (p<0.05) increased from 5.41 to 6.36 mmol⋅l^-1in the experimental group. On the other hand, no significant increases were observed in the control group.
2) Running velocity in the final stages (Vmax) was significantly (p<0.001) improved from 190.0 to 205.0 m⋅min^-1in the experimental group. Such effects were due partly to the improvement of circulorespiratory function and partly to improved efficiency of running motion. However, no significant differences were found in the control group.
3) Submaximal V, HR, and Vo₂/TBW equivalent to 3 and 4 mmol⋅l^-1 and their values relative to the maximum values showed no significant differences before and after the training period in both groups. The improvement of maximal circulorespiratory variables observed in the experimental group suggests the existence of trainability even in young children.

Eight young girls as an experimental group (E group) and another eight as a control group (C group), (all aged 4-5 years), participated in the present study to observe the effects of training from May 1992 through November 1993. E group performed a 915m endurance run on an agricultural road every day except Sundays for an 18 month training period. No special training was given to C group. In May 1992 (T 1), November 1992 (T 2), May 1993 (T 3), and November 1993 (T 4), both groups underwent treadmill tests in order to check aerobic variables such as heart rate (HR) and oxygen uptake (VO₂) during the course of the training period.
Times required for the run became shorter from summer to fall and from winter to spring (shortening phase), whereas they became prolonged from spring to summer and from fall to winter (prolongation phase) . Therefore, there was a definite seasonality of performance endurance. The rates of shortening in the required times observed from summer to fall were considerably higher than from winter to spring, and this was reflected in the significant improvement of maximal running speed on the treadmill (Vmax) and maximal oxygen uptake in terms of body weight (VO₂max⋅ TBW^-1) from T 1 to T 2 as well as from T 3 to T 4. Thus, significant differences were found between the groups at T 2 and T 4. HR levels during the endurance run were close to 95% HRmax regardless of the phase. Accordingly, the prolongation phases, during which circulatory parameters and ventilatory capacity were least improved, could be regarded as a preparatory period for the following shortening period, during which work load intensities furthermore increased the arteriovenous oxygen differences. Thus, when planning research on the effects of training on aerobic work capacity in the field, special attention should be paid to the season and the training period, and the timing of the examination for training effects, or otherwise, misleading conclusions could be drawn.

In order to find out the criteria for the determination of maximal oxygen uptakes of very young children, five boys and five girls, aged four or five years, served as the subjects. They ran on the horizontal treadmill once a day for the constant three minutes on different days. The velocity was increased from the first 100m/min by 20m/min till the last where they could endure no longer for the three minutes. As the consequence, the velocities attained were 100m/min, 120m/min, 140m/min, 160m/min, 180m/min and 200m/min for boys and 100m/min, 120m/min, 140m/min, 160m/min and 180m/min for girls.
The expired airs were collected at rest and whole through the treadmill running.
Heart rates were also continuously registered not only at rest but also during the treadmill running.
The following results were obtained:
1) At the velocities of 100m/min, 120m/min and 140m/min apparent steady states of heart rates and Vo₂ were established within the three miuntes both for boys and girls.
But boys showed lower heart rates and higher Vo₂ during the steady states at a given velocity than girls did.
2) At the last velocity of 200m/min Vo₂max were attained 30 seconds after the start of running for boys and also at the last of 180m/min girls reached Vo₂max 60 seconds after the beginning.
It was, therefore, confirmed that if the work intensity was sufficiently high, Vo₂ max could be reached at the latest between 30 and 60 seconds after the start of work for young children.
3) At the one step lower velocity than the last, namely, 180m/min for boys and 160m/min for girls, the plateaus of Vo₂max were found for the last minute.
4) The heart rates simultaneously observed with Vo₂max ranged from 202.4 to 206.4 bpm and also RQ were all above the unit. Accordingly these values could be regarded as the most important critieria for the evaluation of aerobic work capacity of young children.
5) When the velocity was high, the respiratory frequency sharply rises immediately after the start of running. For the first thirty seconds the breath rates reached 60 to 90/min.
6) If the duration of the running on the horizontal treadmill are constantly fixed three minutes, the upper limit of the velocity where the safe aerobic steady state can be established is 140m/min both for boys and girls.