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Even a modest workout may strengthen the heart

August 02, 2004|Kelly Young | Times Staff Writer

Even a single session of moderate exercise can improve heart health for at least a day, a new study suggests.

It's no secret that frequent and intense exercise can improve heart function, but this is the first time scientists have tested the heart's response to a single, less intense bout of exercise. For this study, 11 healthy young men spent 60 minutes on an exercise bicycle, pedaling at a rate at which they could easily hold a conversation. They had not exercised for at least three days before the study.

Researchers measured the participants' heart rate variability with an electrocardiogram four times after the exercise session.

If a person's heart beats 60 times a minute, it doesn't necessarily pulse in time with the second hand on a clock. Heart rate variability is a measurement of the beat-to-beat differences in heart rhythm.

After exercising, the men had higher heart rate variability than when they were resting.

People with hearts that can change in response to stress -- a high variability -- have lower rates of heart disease. A low variability is a predictor of risk for sudden cardiac death, insulin resistance, and other heart and lung problems.

David Pober, the study's lead author, suggested that exercising every other day could provide lasting heart benefits. People who exercise frequently generally have a higher variability.

"In some biological systems, high variability seems to indicate adaptability in the system," said Pober, a doctoral student in exercise science at the University of Massachusetts Amherst. "This seems to indicate that if you have a perturbation in the system, the heart has a high ability to adapt to the situation."

The variability of the study participants stayed elevated for 22 hours after they finished exercising. Heart rate variability might remain high for a longer period, but researchers did not test beyond 22 hours. Some of the other benefits of exercise, such as reduced blood pressure, last two or three days.

One of the study's drawbacks was that it measured only relatively fit men. "So we don't know how someone who's not accustomed to exercise is going to respond," Pober said.

The results were published in the July issue of the journal Medicine & Science in Sports & Exercise.

Pober's team plans to measure insulin levels and heart rate variability before and after five days of exercise to see whether the variability rate changes over time.

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