Sitting for 20 minutes less a day won't make you 'more muscly'
"Spending just 20 minutes less sitting a day reduces blood sugar levels, improves cholesterol AND even makes you more muscly," is the Mail Online's overly optimistic claim.
Researchers in Finland recruited people who worked in offices and had young children for a study investigating whether training could help cut the amount of time the parents spent sitting. Regular, prolonged periods of sitting puts people at risk of developing diseases such as diabetes and heart disease.
Despite a programme of counselling and a lecture aimed at making people more active during work and leisure hours, people sat for only 21 minutes less for every eight hours during the first three months of the study, and only during leisure time. By the end of the year-long study, people were only sitting for 8 minutes less than those in the control group.
Researchers reported "some small positive changes" in blood sugar during the first three months, and in cholesterol biomarkers and lean leg mass at the end of the study, compared with parents who had not received the intervention. It's not clear how clinically important these changes were.
While it's true that every little helps, there's very much a dose-dependent relationship when it comes to the benefits of exercise: the more you do, the more you benefit.
You should aim to at least meet the minimum physical activity guidelines for adults.
Where did the story come from?
The study was carried out by researchers from the University of Jyväskylä in Finland. It was funded by the Finnish Ministry of Education and Culture, the Ellen and Artturi Nyyssönen Foundation, the Juho Vainio Foundation and the Yrjö Jahnsson Foundation. It was published in the open-access, peer-reviewed PLOS One medical journal so is free to read online.
The Mail Online's interpretation of the study does not stand up to much scrutiny.
The 20-minute figure cited in the headline was sustained for only three months and, rather than making people "more muscly", lean leg mass stayed about the same in people who were on the programme. It's just that those who weren't on the programme lost lean leg mass.
Reduced blood sugar levels lasted only three months, and the changes in proteins related to cholesterol metabolism were small and of uncertain importance.
What kind of research was this?
This was a cluster randomised controlled trial (RCT). In cluster RCTs, groups of people are randomised, rather than individuals. In this case, neighbourhoods in the Finnish city of Jyväskylä were randomised, with the people living in them recruited to either the control or intervention arm of the study. RCTs are usually good ways to measure the effect of an intervention.
However, in this study, the intervention – a lecture and counselling about reducing sedentary time – was not "blinded". People knew whether or not they were receiving the lecture and counselling, which reduces the reliability of the results.
What did the research involve?
Researchers picked 14 neighbourhoods in the city of Jyväskylä, with seven randomly assigned to receive the intervention programme and seven to act as controls.
They recruited parents who had children aged three to eight in kindergartens and infant schools in the 14 neighbourhoods. The parents were recruited either individually or as pairs. There were 133 participants overall, with 71 parents from the intervention neighbourhoods and 62 from the control neighbourhoods.
Parents from the intervention neighbourhoods underwent the study programme of a lecture followed by counselling sessions. Researchers looked to see how activity levels and sedentary time changed over a year, and whether physical assessments also changed.
Everyone had a physical assessment and tests, including measurements of physical activity, at the start of the study, and after 3, 6 and 12 months. These included body composition, blood pressure, and blood tests to measure insulin resistance, cholesterol and blood sugar.
People were excluded from the study if starting body mass index was above 35 (which could be considered as being morbidly obese if they had other health problems), they were pregnant at the start of the study, they had long-term illnesses or if the child had a disability that delayed their development of movement skills.
Diet was assessed through participants keeping diaries for three weekdays and a weekend day at the beginning and end of the study, and on a weekday at three, six and nine months.
The intervention group's lecture explained the potentially harmful effects of being too sedentary. During counselling sessions, parents set goals to reduce their sedentary time at work and at home. During follow-up phone calls, they discussed their progress towards the goals and any problems they'd had achieving them.
The researchers compared the difference between the change from baseline between parents in the intervention and the control groups for:
- total sedentary time
- work sedentary time
- weekday leisure sedentary time
- weekend leisure time
- light activity time
- moderate to vigorous activity time
- breaks from sitting per hour during sedentary time
These were measured by giving people an accelerometer to wear (a device similar to a fitness tracker) for seven days at five points during the study year.
What were the basic results?
After three months, parents who went through the programme showed no changes in their total, workplace or weekend sedentary time compared with parents in the control group, but they were doing better on weekday leisure time:
- Compared with the control group, for every 8 hours, they sat for 21.2 minutes less (95% confidence interval [CI] -37.3 to -5.1).
- After 12 months, they were sitting for just 7.9 minutes less than the control group (95% CI -24.0 to 8.3). This difference wasn't statistically significant – it could have been down to chance.
In the first three months, the programme group did more moderate to vigorous physical activity than the control group, but that was because the control group's levels of activity dropped, not because the programme group did more activity.
There were a few differences in people's biochemical and physical test results.
Out of 12 tests of body composition and blood pressure, there was only one difference (lean leg mass, or muscle) between the groups after 12 months. However, this was mainly because the control group had lost muscle, whereas the programme group's stayed about the same (mean difference between groups 0.48%, 95% CI 0.18 to 0.77).
Of 14 biochemical test results, only two – involving levels of a protein called apolipoprotein A1, related to the metabolism of cholesterol – showed a difference between the two groups after 12 months.
How did the researchers interpret the results?
The researchers said their results showed their intervention "induced a small beneficial intervention effect on weekday sedentary leisure time throughout the whole year". They added that "some small positive changes in biomarkers were observed" at the same time.
They also noted that the initial decrease in overall sitting time achieved in the first three months of the study was not maintained over the year.
Despite the encouraging headlines, the study showed it isn't easy to get people to reduce their overall sedentary time. It's interesting that people were better able to make changes at home – especially when both parents had been through the programme – than in the office.
Future programmes could look at whether workplace interventions, which might include group activities or changes to the office environment, are more successful at reducing time spent sitting.
We don't know the clinical significance of the small changes in some of the physical and biochemical results found in the programme group.
It's surprising that any changes were found at all when the difference in activity levels was so small. One possibility is that the small number of participants and the large number of tests threw up some misleading results.
There are several other limitations to the study:
- It was subject to selection bias. Only 30% of people contacted showed any interest in participating, meaning those who did were likely to be more motivated in the first place, so the results may not be applicable to the general population.
- People may have changed their usual activity level when wearing the accelerometer.
Any effort to help people become less sedentary is to be applauded, but it's likely most people will need to do more than just sitting down for a few minutes less to make a big difference to their long-term health.
While 20 minutes more exercise a day is certainly better than none, if you have been inactive for a while, you should aim to gradually build up your activity levels until you meet the recommended minimum for adults.
Read more advice about getting started with or returning to exercise.
Links To The Headlines
Links To Science
Pesola AJ, Laukkanen A, Heikkinen R, et al. Accelerometer-assessed sedentary work, leisure time and cardio-metabolic biomarkers during one year: Effectiveness of a cluster randomized controlled trial in parents with a sedentary occupation and young children. PLOS One. Published online August 24 2017