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Effects of daily physical activity level on the degree of sympathetic tone.

BACKGROUND
Exercise is recommended for the treatment and prevention of cardiac disorders. Relaxation of the sympathetic nervous system has been considered to be one of the therapeutic mechanisms. However, the means by which the level of daily physical activity affects sympathetic activity remains unclear.


OBJECTIVE
To evaluate the effects of daily physical activity on autonomic nervous tone.


METHODS
Daily physical activity was measured for 5 or more days in 26 patients with various cardiac disorders of NYHA class 1 or 2 and in 6 healthy individuals using an intelligent calorie counter. Recumbent resting ECG was recorded for 3 minutes immediately before waking up and after going to bed using a digital ECG. Low- (Lf, 0.03-0.15 Hz) and high- (Hf, 0.15-0.45 Hz) frequency components were calculated by frequency analysis of the R-R interval, and Lf/Hf ratio was calculated as an index of sympathetic tone.


RESULTS
The average values of energy expenditure and time were 145+/-93.6 kcal/day and 47.8+/-24.3 min/day, respectively. The morning Lf/Hf ratio decreased following an increased physical activity level the day before, but increased with subsequent increase in the activity level in 65.6% of subjects. A negative correlation was observed in 34.4% of subjects, which suggested that an appropriate level of physical activity led to relaxation of sympathetic tone.


CONCLUSION
The daily level of physical activity affects sympathetic tone, and an appropriate level results in sympathetic relaxation. The results of this study provide a useful index to enable patients with cardiac disorder to perform exercise without overloading.