Today we get to hear from Marlou Dirks, a research fellow at Exeter University in nutrition and inactivity. Marlou has a PhD from Maastricht University and ten years of research experience at world-leading Universities. So let’s pass over to more experienced hands…
Key question: What can we eat to help prevent muscle loss during physical inactivity?
Although we know that physical activity is important for our health, at times it can be hard to avoid a period of total physical inactivity. For example, you may need to wear a leg brace or cast when recovering from an injury, or when you are admitted to hospital you might have to stay in bed. Even in young healthy people, these periods of inactivity lead to a loss of muscle mass and health as discussed in Articles #10 and #11. To show this impact of short-term physical inactivity, I ran a study (click here) where we asked 10 healthy people to not leave bed for an entire week, although they were allowed a laptop, books, and occasionally a Playstation (trust me… that’s not as fun as it sounds). After one week, they had lost an incredible 1.4 kg of their muscle mass. This shows how quickly you lose your muscle when you don’t use it, since it takes 10-12 weeks of structured strength training to gain a similar amount. Next to physical activity, nutrition (and specifically protein from the diet) is an important stimulus for building muscle. Researchers currently think that eating between 1.2 to 1.6 g of high-quality protein per kilogram of your body mass (90-120 grams for a 75 kg person) per day is a good target for health outcomes in physically active adults. Because of the scary result from that initial study we wanted to know: ‘what (and how much) should we eat to help maintain our muscle during periods of inactivity?’
In a young person who is recreationally active, a meal with around 20 grams of protein (e.g. a small bowl of Greek yoghurt or an egg mayo sandwich) is enough to maximally stimulate the building of new muscle proteins. However, if this person has their leg immobilized for 5 days, the same 20 grams is no longer enough to give the same stimulus. In fact, the building of new muscle is ~ 50% lower (click here). The muscle becomes more resistant to the building process, which shows how important it is to maintain physical activity if you can. In support, a recent study from Exeter showed that changing the amount of daily protein in the diet has no effect on the amount of muscle that is lost during 3 days of leg immobilization (click here). We showed a similar result when we gave elderly people 20 grams of protein twice a day (on top of their normal diet) during 5 days of leg immobilization, as they lost the same amount as those who did not receive this extra protein (click here). Although we currently do not know if it is at all possible to stimulate the building of new muscle proteins by larger quantities of protein, any meals should likely contain much more than 20 grams to maintain muscle mass, during periods of inactivity.
Physical activity is the strongest stimulus for building new muscle, and it can further increase the effect of eating protein. ‘Normal’ physical activity is likely to be the best option, but sometimes this is not possible, for example if you are wearing a leg cast. A method that has been used in the past to ‘simulate’ physical activity (i.e. muscle contractions) is neuromuscular electrical stimulation. This uses small electrodes that are placed on the skin of the muscle that you want to stimulate, and then a small electrical current can be sent to the muscle, which makes the muscle contract. Using this method, more proteins from a meal were able to be built into the muscle (click here). This research also shows that doing even small amounts of physical activity before eating can improve the benefits of the meal if you are sedentary.
Take home message: Periods of being very inactive can be extremely bad for the health of your muscles. Eating more protein than 20 grams per meal is likely to be needed to maximise the building of new muscle during physical inactivity. Ideally these meals should be combined with some degree of muscle contraction before the meal.
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