Low-level aerobic exercise improves cardiorespiratory fitness
We are always telling our patients to exercise more. It is accepted that poor cardiorespiratory fitness is associated with a higher cardiovascular risk and, indeed, a higher risk of death. It is also accepted that improving fitness can reduce this risk.
Physical activity would seem to be the primary means by which to improve fitness and the current recommendation is for 30 minutes of moderate aerobic activity at least five days per week. The term moderate is often defined as the level of exercise required to induce mild breathlessness.
A study in JAMA has looked at further defining the effects of various levels of physical activity on cardiorespiratory fitness in postmenopausal women with cardiovascular risk factors.
The study enrolled 464 sedentary, overweight or obese postmenopausal women (BMI 25-43) who had a systolic blood pressure between 120 and 160mmHg. The women were randomised to one of four groups:a non-exercise control group (n=102), a 4 kcal/kg/week exercise group (n=155), an 8 kcal/kg/week group (n=104) and a 12 kcal/kg/week group (n=103) for six months. The type of exercise used was walking or cycling.
The primary outcome was aerobic fitness, assessed on a cycle ergometer and quantified as peak absolute oxygen consumption (Vo2abs, L/min). The mean exercise duration per week was 72 minutes in the 4 kcal/kg/week group, 136 minutes in the 8 kcal/kg/week group and 192 minutes in the 12 kcal/kg/week group.
After adjustment for age, ethnicity, weight and peak heart rate, women in the exercise groups had significantly increased their fitness compared with the control group: by 4.2% in the 4 kcal/kg/week group, 6.0% in the 8 kcal/kg/week group and 8.2% in the 12 kcal/kg/week group. Interestingly, there were no significant changes in mean systolic or diastolic blood pressure in any of the exercise groups compared with the control group.
This study has shown that even 72 minutes of relatively low-level exercise can significantly improve cardiorespiratory fitness. Naturally, higher levels of exercise produce greater improvements.
It is also encouraging to note that the dropout rate was low, and although no blood pressure or weight reduction was seen, a reduction in waist circumference was observed in participants in the exercise groups. This is encouraging considering the association between abdominal adiposity and the metabolic syndrome.
The message is clear: some exercise is better than none, but more is best.
Church TS, Earnest CP, Skinner JS et al. Effects of different doses of physical activity on cardiorespiratory fitness among sedentary, overweight or obese postmenopausal women with elevated blood pressure. JAMA 2007;297:2081-91Dr Peter SavillDr Peter Savill Reviewer
Dr Peter Savill
GPSI Cardiology, Southampton