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KYOTO, JAPAN. Obesity is becoming increasingly common in developed countries and is associated with
an increased risk of diabetes, hypertension, heart disease, and other chronic diseases. A low heart rate
variability (HRV) is associated with an increased risk of sudden death and is a common feature in obese
individuals. HRV is a measure of the variation in the time interval between individual heartbeats. It has two
main components, a low frequency component (less than 0.15 Hz) which is primarily an indication of the
activity of the sympathetic nervous system (SNS) and a high frequency component (greater than 0.15 Hz),
which is an indication of the activity of the parasympathetic nervous system (PNS). Researchers at Kyoto University now report that regular aerobic exercise not only reduces body mass index (a measure of obesity) and improves lung function, but also produces a significant increase in HRV. Their experiment involved 18 obese middle-aged men and women with an average body mass index (BMI) of 27.3. Obesity is defined as a BMI over 25. The study participants underwent a 12-week aerobic exercise program consisting of three weekly sessions of 30-minute exercise on a stationary bicycle. At the end of the program the average BMI had dropped to 25.9, aerobic capacity had improved significantly, and HRV (total power) had increased from 459 to 1042 ms2 (milliseconds squared). The low frequency component (SNS) increased from 349 to 695 ms2, and the high frequency component (PNS) from 146 to 348 ms2. The researchers believe that it is the increase in sympathetic (adrenergic) activity that is primarily responsible for the weight loss. Increased sympathetic activity can also be induced by exposure to cold and by ingestion of capsaicin (hot peppers). Capsaicin is known to increase energy metabolism through the release of neurotransmitters (catecholamines) that activate the SNS. The researchers conclude that
regular aerobic exercise benefits obese individuals through weight loss, improved lung function, and a
beneficial increase in heart rate variability.
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