For this week’s theme of physical inactivity, our first expert is Ryan Marshall, a PhD student at the University of Birmingham, who is studying the impact of being too sedentary on the health of our muscles.
Key question: Just how bad is inactivity for our muscles?
How many of you reach the “10,000 steps per day” set by your Fitbit or Apple Watch? Even more interestingly, how many of you have kept this up during the pandemic? I’ll be the first to admit, my step count has become dangerously low over the 12 weeks of lockdown. This, begs the question, what are the consequences of such drastic periods of physical inactivity, and can we do anything about it?
Relatively short periods of inactivity can have serious consequences for your health. We know this from studies where we ask volunteers to do a two week period where they take less than 1,500 steps each day... Considering lockdown has lasted for 12 weeks, we have probably all experienced a two week period with a similarly low step count. So, what does that mean for our health? Well, a research group at the University of Copenhagen have showed that two weeks of low physical activity levels led to a 57 % increase in blood insulin levels in response to drinking a sugary drink. As you may recall from Article #7, insulin is the hormone that helps to regulate blood sugar. As the participants had to produce more insulin to control their blood sugar, this suggests their bodies were becoming less responsive to insulin’s effects. The same group of researchers also showed that skeletal muscle became less responsive to insulin and this was also accompanied by a ~ 3 % reduction in leg muscle mass (roughly speaking that’s a 300 g steak!!) and a ~7 % reduction in fitness levels.
If it’s that bad for young adults, imagine the consequences of inactivity is for older people?
This is exactly what my boss at The University of Birmingham, Dr Leigh Breen wanted to find out in 2013, when he was at McMaster University in Canada. He found that in older adults (~72 years of age) they became a lot less responsive to insulin and showed a loss of ~4 % in leg muscle mass following a period of very low levels of physical activity. To put that in perspective, older adults typically lose muscle at a rate of 1-1.5 % per year after the age of 50 (that’s just part of ageing). Therefore, in just two-weeks, older adults lost TWO YEARS worth of muscle!! Normally the muscles in our body our constantly cycling between breakdown (during fasting) and building (after we have eaten meals), so that over a 'normal' day a balance is achieved. However, the research in older people also showed that skeletal muscle was a lot less able to make new proteins in response to feeding. What is alarming about these results is that many older adults never regain the muscle lost during periods of inactivity, which makes them more likely to get diseases and experience disabilities.
Sometimes (for example when you are in hospital) it can be difficult to be physically active, and my research looks at dietary strategies that might help to prevent muscle losses in this scenario. For a review of our research in this area you can click here and strategies include making sure you are having a healthy dose of protein with every meal (we are going to learn more about nutrition during inactivity in upcoming blog posts). However, for most of us, it is possible to increase our physical activity levels a bit more and this should definitely be a target. To demonstrate this, a recent review (in June 2020) showed that even if you cannot meet the 10,000 steps/day recommendation, every increase of 1000 steps/day has benefits for your health. Our next expert is going to delve into this even more and discuss why breaking up periods of sedentary time (i.e. having small activity breaks) has health benefits!! You can click here to jump to Part 2 of the 'Don't Stop Moving edition'!!
Take home message: Being physically active is really important to keep your muscles healthy. Even short periods of physical inactivity can results in losses of muscle and make your muscle less responsive to the hormone insulin.
Don't forget to subscribe to the blog (click here) and check out Part 2 of our 'Don't stop moving' addition, for more information about the benefits of increasing those steps...
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