The purpose of this lecture is to introduce how aquatic exercise is an attractive training method, especially for maintaining the cardiovascular fitness, during recovery from musculos-keletal injuries of the lower legs and/or from obesity. Though the energy expenditure of vertical movement in water is less than that on land due to the effect of buoyance, walking/running in water increases the energy metabolism largely enough to maintain the cardiovascular fitness level. In addition, water running on the spot with flotation device is capable of eliciting metabolic responses comparable to treadmill running on land. Therefore, comfortable and useful facilities for aquatic exercise should be constructed in each province for both healthy and injured persons to maintain and improve their cardiovascular fitness.

In order to investigate an effect of the excess fat of obese men on the respiratory-cardiovascular system, VO₂max was measured for seven obese, 16 ordinary and seven lean men. All subjects were university students, ages 18 to 25 years. Body composition was determined by densitometry. Furthermore, six non-obese young men participated in an added-weight experiment so as to estimate an effect of the excess fat of obesity. Results showed that there were no statistically significant differences in the absolute values of VO₂max, VEmax, and HRmax among the groups. Concerning the relative value of VO₂max to body weight, the obese group showed a significantly lower value of 40.4 ml/kg-min than the lean and ordinary group values of 51.5 and 48.8 ml/kg-min, respectively. However, no significant difference was found between the relative values of VO₂max per lean body mass of any of the groups. VO₂max for the obese group was 54.0 ml/kg-min, 56.0 for the lean group and 57.7 for the ordinary group. Such trends were very similar to the results of the added-weight experiment. Based on the values for the subjects in this study, this leads to the conclusion that the excess fat of obese men might act only as an inactive load and might not affect the ability of the respiratory-cardiovascular system. Besides, the threshold of obesity for men proposed by Behnke and Wilmore might be reasonable from the viewpoint of the absolute and the relative values of VO₂max.

Oxygen intake, pulmonary diffusing capacity (DL), pulmonary membrane diffusing capac ity (DM) and pulmonary capillary blood volume (Vc) were measured at rest and during maximal and submaximal work, with Filley's steady state technique on 3 athletes (middle distance runners) and 5 non-athletes. The results obtained in this study were as follows
(1) At rest, DL, DM, Vc in athletes were 28.3±3.7 ml/min/mmHg, 52.2±5.3 ml/min/ mmHg, 124.1±41.8 ml respectively, and in non-athletes were 25.6±1.0 ml/min/mmHg, 47.5±7.5 ml/min/mmHg, 114.7 ± 25.9m1 respectively.
(2) During submaximal works, DL, DM and Vc increased together with oxygen intake. At the same level of VO₂ athletes showed greater DL, DM and Vc than those of non-athletes. Contact time exponentially decreased as oxygen intake increased.
(3) At maximal work, athletes showed significantly greater max VO₂ DL, DM and Vc than those of non-athletes. But, contact time of athletes was not significantly greater than that of non-athletes.
(4) The results demonstrate that a higher DL, DM and Vc is accompanied by a higher aerobic capacity, a larger ventilatory capacity, and a larger cardiac output.

The present study was designed to investigate the effects of low altitude training on swimming performance with setting the same duration (3-wk) and the same level of altitude (2, 300m) . Eight male (Gm₁) swimmers aged 13 to 19 years and four male (Gm₂) and eight female (Gf₂) swimmers aged 13 to 18 years sent to Mexico City, and they conducted swimming work outs. All of them were top Japanese swimmers of various events. They repeated the swimming training twice a day continuously for four days with one day rest. Hemoglobin concentration (Hb), red blood cell count (RBC) and hematocrit (Hct) were determined before, during and after the altitude training several times. The values of Hb, RBC and Hct of all three groups increased significantly from before training to after training except Hb in Gm₁. On the other hand, these three variables did not necessarily increase during the altitude training. Gm₁ and Gf₂ tended to increase Hb and RBC during the training. As for swimming performance at sea level, the individual best swimming records were improved significantly in 200m events, but not in 100m events in Gm₁. Therefore, it may be concluded that 3-wk altitude (2, 300m) training possibly improve swimming performance in the events equal to or longer than 200m at sea level.

The explosive power output of both legs during extension movement was assessed in 271 male (aged 16-84 yr) and 248 female (aged 16-82 yr) subjects, and the table of evaluation for the value obtained was prepared with the function of sex and age. From a sitting position on a seat, leg extension movement was performed toward the foot plate in the forward, to which the body mass of each subject was applied as a resistance. The reliability of the power measurement was ascertained from the result that the coefficients of variation were under 5 x 10^-2 when the power output of 6 subjects was measured once a day for 10 days. On both sexes, the power output per body mass declined linearly with age. The regression equations between age (x) and the power output per body mass (y) were as follows.
male: y=-0.22 x+28.38 (r=.659, n=271; p<0.001)
female: y=-0.13 x+18.36 (r=.583, n=248; p<0.001)
For all groups classified by 10 years, the male indicated greater value than the female in corresponding groups. The ratio of the value for the female relative to that for the male was between 64.8% and 72, 0%. These results suggested that the power output for the male decreased at a higher rate, and the sex difference of it decreased as the age increased.

The metabolic rate, HR and thermal responses of 26 children, aged 7-8 years (6 boys, 7 girls) and aged 9-11 years (7 boys, 6 girls), were measured during head-out immersion in water. In the water bath, a bicycle ergometer was set and water temperature wes maintained at 26±1°C. Thirty minutes measurements of heat production (cal⋅min^-1⋅m^-2), HR, rectal (T_re) and skin (T_sk) temperatures were obtained under experimental conditions of resting and bicycling in water.
The rate of decrease in HR and T_re were significantly greater in the younger group than the older, irrespective of sex, in resting condition (P<0.001, P<0.01, respectively), but any differences could not be found in bicycling condition.
Heat conductanc (K) from body surface were calculated. In resting condition in water, older girl group showed K=94.1 (cal⋅m²⋅°C ⋅min^-1) and younger boy group K=142.2 and in bicycling condition in water they were 213.8 and 276.9, respectively.

The purpose of this study is to conduct the examination of heart rate and speed variations with respect to the various interval trainings of swimming. One trained, one post-trained and one untrained swimmers were employed for this study. The experiment was conducted during the summer of 1968. The temperature of atomosphere varied from 30°C to 33°C and that of water from 27°C to 29°C.
The data of heart rate were obtained from the record of ECG. Two electrodes or ECG consisting of silver cups of 10mm in diameter were attached to the skin over sternum. In order to avoid mechanical and electrical disturbances, the electrodes were tightly fixed through the following procedures;
1) The electrodes were pasted on cleaned skin with ECG jelly.
2) The adhesive plaster was placed over the electrodes.
3) The adhesive plaster was coated with wax.
The wire of 20 meters was used to connect the electrodes and the recorder. On trial of interval training was consisted of two phases; 1) The active phaseTo swim 50 meters according to his swimming ability. 2) The rest phase.To take a 0, 5, 10, 20, 30, 45 or 60 seconds interval between each 50 meters swimming. Each trial of training was repeated ten times.
Results are as follows;
1) The longer the rest period is, the higher the swimming speed is.
2) All swimmers swim 50 meters at 60-80% of their maximum speed and the percent of the trained is higher than that of the untrained.
3) Maximum heart rates of the trained, the post-trained and the untrained during tenth swimming are 188, 180 and 173 respectively, which are the same in every trial.
4) Decreasing rates of heart rate during the rest period are 10 under in 5-10 seconds interval, 15-25 in 20-30 seconds interval and 20-50 in 45-60 seconds interval,

Oxidation of lactate at rest (RE, n=4), or after short strenuous exercise (EX, n=6) was investigated in rats. Food and water were given ad libitum before experiment. In EX, rats ran to exhaustion at the speed of 80-100 m·min^-1. Immediately after exercise, 4 μCi of (U-¹⁴C) lactate was injected into aorta through an indwelling catheter. In RE, (U-¹⁴C) lactate was injected into the rats at rest. Expired gas was collected by a Brooks type bottomless chamber on treadmill belt for 120 min. In EX, exercise duration was 109±18 sec (mean±SE), and maximum blood lactate concentration after the exercise was 23.7±2.1 mM (mean±SE) . Cumulative percent recovery of ¹⁴C as ¹⁴CO₂ for 120 min was 48.5±2.8% for EX and 61.7±0.9% for RE (mean±SE) . Significant difference was found between these two rates (p<0.01) . After 50 min of recovery, mean volume of ¹⁴CO₂ expired per min in RE was significantly greater than that in EX (p<0.01) . Mean volume of ¹⁴CO₂ expired per min per VCO₂ in RE was always greater than that in EX, and significant difference was found at 7.5 min of recovery (p<0.01) . It is concluded that although the rate of recovery of ¹⁴C as ¹⁴CO₂ after exercise is lower than that at rest, the major pathway of lactate metabolism after short strenuous exercise is oxidation.