Physical activity has long been recognised as protective against heart disease, but researchers have disagreed about how much exercise is needed and at what intensity to achieve this potential benefit. Furthermore, there has been a lot less research on women than on men.

Now a group of researchers from Spain have set out to fill this knowledge vacuum with a study of the links between physical activity, fitness and blood lipid levels in just over 400 premenopausal women.

The participants completed a comprehensive questionnaire designed to ascertain:

1. the total amount of physical activity they had engaged in over the past year, in terms of METs per minute per day;
2. the relative contributions of light, moderate and vigorous activity to the overall total. Light activity was defined as 4 METs or less, moderate activity as 4.5-7 METs and vigorous activity as 7.5 METs or more.

The researchers took blood samples to measure the women’s lipid and hormone levels and set them a treadmill exercise test to assess their fitness. They also looked at the women’s diet and other lifestyle measures, body mass index and family history of heart disease. Their key findings were as follows:

• Only moderate intensity physical activity was significantly associated with a ‘desirable’ lipid profile in terms of heart disease, with relatively low levels of the ‘bad’ LDL cholesterol and high levels of the protective HDL cholesterol;
• The association between moderate physical activity and HDL cholesterol was independent of body fat mass, although the association with LDL cholesterol was dependent on body composition;
• Only vigorous intensity activity was directly associated with fitness, as defined by VO2max.

A similar study on men found a more marked association between exercise and the blood lipid ‘profile’, with vigorous intensity exercise the most protective. ‘The differential association between genders may be related to the better lipid profile of women,’ the researchers suggest, ‘which may be more difficult to improve with physical activity.’

They acknowledge that the lack of an observed association between vigorous activity and lipids could be related to the low number of participants who undertook this type of activity. But they do not rule out the possibility that ‘the beneficial effect of physical activity on serum lipids in women is mainly dependent on moderate energy-expenditure activities.’

‘Another relevant result of this study is that whereas moderate intensity physical activity was associated with a better lipid profile only vigorous intensity physical activity was associated with physical fitness. These results support the idea that physical activity could be more important than physical fitness when regarding health outcomes.’

Int J Sports Med 2006; 27:911-918