The next big thing in physical activity research: sitting doing nothing. Steve Blair (University of South Carolina), a major player in the physical activity research world, suggests that the pattern of inactivity is important. Sedentary behaviour, irrespective of the overall level of activity is itself a risk factor- sitting doing nothing may be harmful, even if you exercise. This evidence is from epidemiological studies where residual confounding is the greatest  potential limitation, but the findings could have major potential implications. You might immediately think of adolescents watching  television or video games, but it is relevant to all of us whose work  involves endless hours sitting in front of a computer.

Pregnancy is no excuse for doing nothing. Women worry if exercise may lead to miscarriage but Katrine Owe (Norwegian School of Sports Science) showed, in two large Scandinavian database studies (200K women), that the risk is very small. There may be a very slight increase – the effect was greatest in retrospective work but was minimal in prospective studies and there were no problems after 18 weeks. There was no overall effect on mean birth weight but there were fewer low birth and high birth weight infants among women who exercised.

Physical activity reduces the risk of cancer. Many epidemiological studies show a reduced risk of colorectal, breast, prostate, endometrial, and lung cancer associated with physical activity- but how? Ann McTiernan (Fred Hutchinson Cancer Research Centre) and her group tried to disentangle the relationship with obesity, especially in breast cancer and found that the protective effect of  physical activity was much less in obese women. The definitive intervention would be a randomised controlled trial – long term and impractical. So, they looked at the effect of exercise on biomarkers and found that in breast cancer, diet plus exercise had the greatest effect in reducing post menopausal sex hormones. She also described a remarkable randomised controlled trial on the effect of exercise on colon crypt cell  proliferation (ki – 67) by biopsy- where healthy volunteers agreed to have repeat sigmoidoscopy. They found that men (who had better adherence to the exercise programme than women) had a greater reduction in cell proliferation with activity.

Exercise research has moved on. The benefits of physical activity are widely accepted. Researchers are looking more closely at the preventive mechanisms and the effect in clinical subgroups. Studies of general physical activity prevalence, adult and childhood obesity, and patterns of self reported behaviour are of lower priority. We know what the world looks like – now it’s time to try to change it.

Domhnall MacAuley is primary care editor, BMJ