Even A Small Amount Of Exercise Increases Fitness In Overweight Older Women
The study is published in the Journal of the American Medical Association (JAMA).
Despite the fact that low levels of cardiorespiratory fitness are linked to high risk of cardiovascular disease (CVD) and death from a number of causes, and that improvement in fitness reduces these risks, very little is known about the link between exercise and fitness, such as how much exercise is needed to produce different levels of fitness.
The study was led by Laboratory of Preventive Medicine Research director at Pennington Biomedical Research Center in Louisiana State University, Dr Timothy Church, who with his co-researchers enrolled 464 sedentary and overweight or obese postmenopausal women with a mean age of 57 and mean Body Mass Index (BMI) of 32.
They randomly assigned the women to 1 of 4 groups with different levels of exercise for 6 months and measured the change in aerobic fitness.
Three of the exercise groups required the women to expend energy at 50, 100 or 150 per cent of the National Institutes of Health Consensus Development Panel recommended physical activity dose. The fourth group was a no-exercise group.
The exercise that was prescribed for the exercise groups was a moderate intensity programme using an exercise bike or treadmill three or four times a week for six months for a mean total duration of 72, 136 and 198 minutes per week respectively.
The women's aerobic fitness (peak absolute oxygen consumption) was measured using a cycle ergometer.
The results showed that the women's aerobic fitness increased significantly according to how much exercise they were taking each week. The increases were about 4 per cent in the 72 minutes per week group, 6 per cent in the 136 minutes per week group and 8 per cent in the 198 minutes per week group. The average peak absolute oxygen consumption at the start of the intervention period was 15 mL/kg/min, so these increases were above that.
The results were independent of age, weight, fitness at the start of the study, and ethnicity or race.
None of the women did more than the prescribed exercise, and there was no change in other cardiac risk factors during the 6 months, such as body weight, body fat, cholesterol levels and blood pressure.
Dr Church and colleagues concluded that:
"In this study, previously sedentary, overweight or obese postmenopausal women experienced a graded dose-response change in fitness across levels of exercise training."
In a comment in Journal Watch, Dr Thomas L Schwenk said that these findings confirmed what many doctors have been saying to their patients for some time, and he refers to an accompanying editorial in JAMA by Dr I-Min Lee that endorses the advice, "some exercise is good, and more is better".
However, Schwenk said that:
"Both baseline and final levels of maximal oxygen uptake were discouragingly low, and intervention patients did not change their baseline level of walking separate from the exercise program, despite considerable education and encouragement."
"The search for effective ways to promote exercise continues," he noted.
Cardiorespiratory fitness, or aerobic fitness, is the ability of the circulatory and respiratory systems to deliver oxygen to skeletal muscles during sustained physical activity or exercise.
The more regular and frequent the exercise, the more efficient the systems become at oxygen delivery because the heart muscle gets bigger and more able to pump blood with each beat. The number of smaller blood vessels in the muscles also increases, giving more pathways for oxygen to get to the working skeletal muscles.
"Effects of Different Doses of Physical Activity on Cardiorespiratory Fitness Among Sedentary, Overweight or Obese Postmenopausal Women With Elevated Blood Pressure: A Randomized Controlled Trial."
Timothy S. Church, Conrad P. Earnest, James S. Skinner, and Steven N. Blair.
Vol. 297 No. 19, May 16, 2007.
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