ABSTRACT
Long term physical training is known to cause a change of cardiac functions and this effect is observed at various levels of the heart (from whole heart to subcellular level), although its mechanism is not fully understood. It is reported that cardiac hypertrophy and decreased heart rate can be observed as effects of long term physical training, but change of the catecholamine content in heart tissue induced by training is controversial.<BR>In the present experiment, long schedule of short daily swimming episodes was employed to observe the effect of mild physical training on cardiac functions of rats in the growing stage. We measured body weight, heart weight, heart rate under light anesthesia, variation of R-R-interval of electrocardiogram, and catecholamine contents in cardiac muscle.<BR>1) Wister rats were divided into 2 groups 3 weeks after birth. One group rats was kept sedentary in cages, and the other group was required to free swim in a tank containing water at 30°C. At the beginning of the programme, swimming time was 10 min. Swimming was applied 5 days a week for up to 14 weeks, and swimming time was gradually increased to 30 min.<BR>2) Body weight of rats in the trained group was significantly less than that of the controls, and the heart weight to body weight ratio in the trained rats was significantly higher than in the controls.<BR>3) In the exercised rats, the R-R interval of the ECG was longer than that of the controls, and there was a tendency for the variation of R-R interval in the trained group to be larger than that of the controls.<BR>4) At 10 and 17 weeks, rats from each group were sacrificed after or without a 30 min test swim for measurement of catecholamine content of the ventricular muscle. One time swimming for 30 min increased dopamine content, but did not change norepinephrine content except for the trained group at 10 weeks. There was no significant difference in cardiac catecholamine contents in the rested state of the control and trained groups at 10 and 17 weeks.<BR>5) Results were interpreted as follows: One time swimming for 30 min influences the activity of the autonomic nervous system innervating the heart, and catecholamine metabolism at nerve terminals of the sympathetic nervous system. Long term mild swimming does not cause permanent change of catecholamine contents, and the low heart rate in the trained group cannot be soley explained by the decreased activity of the sympathetic nervous system.
ABSTRACT
1) Children's data (10-18 years old) of back strength, height, grip strength and running long jump from data book of Japan Education Ministry (1964-1981) were analyzed. Back strength was mainly studied and was compared with other data (grip strength etc.) . The groups with high average values for back strength at 10-14 years old did not necessarily show high values for back strength at 17 years old, or vice versa. Values for back strength at 10-14 years old were not significantly correlated with those at 17 years old.<BR>2) Using the data from data book mentioned above, tension of deep back muscle (FMUS) was calculated based on kinetic models (FMUS. I, II, III) . Calculated FMUS values were 3-5 times larger than measured back strength values at each age.<BR>3) Relative change of back strength and FMUS in 1964-1981 were compared. All values for back strength were lower than those for FMUS except in 1967. During the late 1960th and the 1970th, average back strength values gradully decreased, but the decrease of FMUS was less obvious than that of back strength.<BR>4) Based on the data of 422 children (7-12 years old, male and femele), values of diaphragm area were approximated with some assumptions, and then FMUS values were calculated. FMUS values calculated by approximate diaphragm area were significantly larger than those calculated by constant diaphragm area (465 cm2) .<BR>The figure for getting FMUS values easily was offered to avoid troublesome calculation. This consists of two graphs, and one can read FMUS values with reasonable precision. Parameters needed for getting FMUS values are sexuality, height, body weight and back strength.