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Physical Activity – How much keeps you going?

Comment by Nicolle Kraenkel, EACPR Exercise, Basic and Translational Research Section


Sedentary behaviour has evolved to be acknowledged as a lifestyle-related cardiovascular risk factor, as has physical activity. Although both parameters might seem as two sides of the same coin at first look, in combination they might indeed provide a more comprehensive picture of a person’s metabolic risk profile. The recent study by Bell et al. therefore investigated the associations of physical activity and leisure time spent sitting with obesity and clustering of metabolic risk factors, namely, hypertension, high triglyceride levels, low HDL levels, hyperglycaemia and insulin resistance. They were able to benefit from data of the British Whitehall II study (1), an occupational cohort of 3670 civil servants. Indeed, the high case number still available at this late follow-up time point is a great strength of the study.

The study provides additional evidence of the impact of behavioural moderate-to-high physical activity on parameters influencing cardiovascular risk, such as metabolic state and obesity. The study observed interaction between both parameters of lifestyle – intensity of physical activity, and leisure time spent inactive – but also some independent influence on outcome – obesity and clustering of metabolic risk factors. Analysis of combined associations of physical activity and leisure time spent sitting with incident obesity at 5-year and 10-year follow-up show – not surprisingly – the lowest odds ratio for the group with high physical activity and low sitting time. For the clustering of metabolic risk factors, however, the combined intermediate groups fared best after 5 as well as after 10 years. This result is surprising and needs to be considered well, both for the potential improvement of further studies, as well as for the development of future hypotheses.

One crucial point is the evaluation of lifestyle parameters – which might be subjective if based only on participants´ own assessment - over the whole study period, especially for long observation times, and adjust for their changing over time. For future studies, novel equipment, such as wearable technology or mobile phones might be helpful in unbiased tracking of physical behaviour over long time periods.

Another potential reason argued by the authors is the higher use of antihypertensive and diabetic drugs – affecting metabolic risk factors - in the intermediate groups as compared to the high activity/low sitting group.  

Importantly, this kind of studies might help to identify parameters optimising patients´ long-term adherence to increased physical activity lifestyles together with the clinical parameters which benefit most from a long-term change in lifestyle, however small it is, as long as it can be kept up.

After all, experience tells us that the best exercise protocol is not effective if it is not suited to be kept up by a large part of the population over long time periods.

(1) Marmot MG, Stansfeld S, Patel C et al (1991) Health inequalities among British civil servants: the Whitehall II study. Lancet 337: 1387–1393