Aerobic exercise good for the heart

New research has revealed that aerobic exercise does more than just reshape the body of patients with stable heart failure.

The study suggests that aerobic fitness programmes are able to turn an enlarged heart into a trimmer, more efficient organ for pumping blood throughout the body.
 
It showed that when patients with heart failure did aerobic exercise several times a week, the oversized heart became significantly smaller and better able to pump blood.
 
Researchers were surprised to find that those who added weight lifting to the exercise routine to enhance muscle strength did not enjoy a similar improvement in the heart’s size or function.
 
"If I were to choose a type of exercise training for a patient with heart failure, I’d choose aerobic exercise," said Mark Haykowsky, an associate professor of rehabilitation medicine at the University of Alberta in Edmonton, Canada.
 
"It’s aerobic training that provides the greatest benefit [to such patients]."
 
Overall, the total direct medical cost of heart failure in the UK each year is currently just over £625 million.
 
In most cases, heart failure is the result of years of high blood pressure or damage from a heart attack.
 
Over time, the heart becomes enlarged, misshapen, and too weak to effectively pump blood, a process known as remodelling. As a result, patients typically become short of breath even with very little activity.
 
For many years, doctors recommended that people with heart failure avoid exercise. In some cases, patients were even put on bed rest in an attempt to relieve the heart of any extra stress.
 
Over the last decade, however, it has become increasingly clear that exercise is good for patients with heart failure, not only reducing symptoms and allowing patients to live more active lives, but also reversing some of the harmful hormonal changes that take place as the body attempts to compensate for a weakened heart.
 
Previous studies have reported conflicting results on the effect of exercise on the heart’s size and function, however.
 
"We knew that exercise could improve fitness and exercise capacity by about 15 per cent, and that exercise could make muscles stronger and larger," said Dr Haykowsky. "But we didn’t know the effects of exercise training on ventricular remodelling."

Analysing the ejection fraction

For the study Dr. Haykowsky and his colleagues analysed data from 14 separate randomised trials involving a total of 812 patients with heart failure.
 
Each of the trials quantified the effects of exercise by measuring changes in ejection fraction, the percentage of blood pumped from the left ventricle to the blood vessels with each beat of the heart.
 
About half of the studies also measured the heart’s size, both at the end of diastole, the part of the cardiac cycle when the heart is relaxed and filling with blood, and at the end of systole, when the heart is squeezing and forcing blood out into the circulation.
 
In nine studies, patients did aerobic exercise such as walking or bicycling for 20 to 60 minutes approximately three times a week, with an intensity equal to 60 per cent to 80 per cent of their peak ability.
 
In another four studies, patients supplemented aerobic exercise with strength training, and in one study, patients did only strength training.
 
Study participants were clinically stable but had markedly abnormal heart function, with an average ejection fraction of just 23 per cent - a normal ejection fraction is 50 per cent or greater.
 
The analysis showed that ejection fraction improved significantly in patients who did aerobic training (2.59 per cent, on average).
 
Similarly, the patients' enlarged hearts became significantly smaller, with a reduction in both end-diastolic and end-systolic volume.
 
By comparison, patients who combined aerobic exercise with strength training showed no significant improvements in ejection fraction or the size of the heart.
 
The single study that evaluated strength training alone showed a drop in ejection fraction, but it was not statistically significant; the study did not measure changes in the size of the heart.
 
Dr Haykowsky speculated that weight-lifting and other forms of strength training may not have shown the benefits of aerobic training in reshaping the heart because strength training results in a heightened pressure load, which may actually increase the stress on the heart.
 
The research was published in the 19 June issue of the Journal of the American College of Cardiology (JACC).
 

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