by Adrienne Berard
August 13, 2021
Michael Deschenes is Professor and Chair of Kinesiology & Health Sciences at William & Mary. He specializes in the neuromuscular system, the nerve network that connects our brain to our muscles. In a study published in Experimental Gerontology, Deschenes and a team of four W&M student co-authors examined the neuromuscular system during endurance training with the aim of finding how its response varies with age.
The team found that after continuous stimulation, young tired muscles produce the same force as old tired muscles, meaning that young muscles can behave like older ones when exhausted.
William & Mary News spoke to him about a recent study that made headlines, which he wasn’t involved in, which found that metabolism doesn’t slow down with middle age, as is popularly believed.
Let’s talk about this metabolic study that just got published in Science. It has been described as “groundbreaking” and “shocking” by the media, but your decades of research into age and exercise seem to demonstrate just that point – that age really isn’t why we put on weight and slow down in middle age.
It sounds so smug to say this, but the conclusions were in no way surprising to me. When I first saw the coverage, I thought, “Wow! It’s going to turn everything upside down. ”One might think from the headlines that the results were earth-shattering – that this study would completely redefine the field, but the conclusion was exactly what I would have predicted.
In fact, throughout my research career I’ve found that metabolic rate is associated with changes in muscle mass, which is unrelated to aging as people think.
For example, let’s look at the first year of life when your metabolism skyrockets. Well then you build up all of these muscles. Remember what you weigh when you are born compared to what you weigh at a year old. But if you think about it, we basically keep the same muscle mass for a good portion of our adult lives, ages 20 to 60. This means that our metabolism should also be roughly the same during this time, which this study found.
Media tends to focus on the results, but in this case the methods have been quite intriguing to me.
Necessarily. It deserves a landmark study because of the way they did it, because of the sheer scope. That really blew me away. They had such a comprehensive set of data that you can trust their claims very much. Think about it, they had six and a half thousand people aged eight days to 95 years – and they had good, effective metabolic rate measurements for each of those people. That is remarkable in itself, but the results were not remarkable to me. Still, the results were of critical importance to the public.
What is so important for the public to understand?
The study highlights that your body is a work tool and we forget that it was always intended to be a work tool. It was never meant to sit like a potted plant all day. Our lifestyle makes us gain weight and then we blame things like our aging muscles or our metabolism, but the reality is that our bodies are not designed to be sedentary.
We are built to be working tools to gather food, defend ourselves from predators, build shelter, and transport water. On the whole of humankind, we have only recently become a sedentary species – and we are suffering the health consequences of this.
It doesn’t take much to reverse course. We just have to get more active again, not really hard training, but steadily. What we see in this study, if you look at the time components, they correspond exactly to how we gain and lose muscle mass over the course of our lives.
Even in this first year we get all types of tissue including muscle mass, and muscle mass is very metabolically active. By the time you reach adulthood, when you are a grown man, your muscle mass is around 40% of your total body weight. If you are an adult female, it is 33% of your total body weight. So it is massive in terms of its contribution to your metabolic activity.
When we start to lose it, we run into problems. Not only because we’re not doing the exercises we need to be able to stay strong, but also because we’re losing muscle mass which can lead to you having blood sugar control problems or developing osteoporosis, because strong muscles mean strong bones. If you don’t exercise, you don’t care about all of these other parts of you.
Let’s talk about the 60 year mark that the metabolism study outlines. What in your research led you to understand what this study shows is that our metabolism doesn’t slow down until we are 60 years old?
I sound like a broken record, but it’s all about movement. That’s the catch. This comes back to what I’ve been saying all along, you need to maintain muscle mass as you get older. It’s critical. This study only confirms what I said that it is actually more important for older people to exercise than younger ones.
For example, look at the changes in metabolic rate they talk about in the study. They break it down into four categories: birth to one year old which has an incredible spike in metabolism which makes sense because you are piling up all kinds of new muscle tissue.
Then there is one to 20 years old when your metabolism starts to drop or even get off, and then there are 20 to 60 years old where it stays the same for about 40 years. Only in the final phase, after the age of 60, does it begin to decline. All of this makes perfect sense when you think about our neuromuscular system.
At the age of 60 we start to lose more skeletal muscles, because then we start apoptosis, the cell death of motor neurons. When our motor neurons die, so do the muscle fibers that activate them. When we lose this muscle mass, our metabolic rate will go down.
But again, exercise can help restore this, or at least stop how fast it falls off. There really isn’t much you can do to stop it because, for some reason, by nature or God’s intervention, whatever, it is by age 60 when you have these motor neurons dying and subsequent loss watch muscle mass.
What should we learn from their – and your – conclusions about aging?
For the elderly, it is really important to maintain muscle mass as much as possible. Because of this, experts in the field now believe that resistance training, such as weight lifting, is more important than aerobic training for the elderly. Maintaining this power allows them to engage in daily living activities such as climbing stairs, getting in and out of cars, carrying food, etc.
And that is true of all Americans in a broader sense. I started studying the effects of exercise in the mid-1990s. That was the first time health-related exercise recipes existed – and that wasn’t training for the Olympics or even the local college team, it was just to stay healthy.
We found that for that small amount of exercise, you get the lion’s share of the benefits. When I started this research, just under 25% of Americans were doing the bare minimum of activities that they had to do for any health benefit. That’s 20 minutes here, 20 minutes there, we’re talking about mowing the lawn or walking around the supermarket. That was two or three decades ago, and now about 23% are doing the bare-bones.
We’re not getting this message across, or at least people are not taking the message. We know what’s important, people just can’t or won’t. And here we fail as a field by getting people to take care of their bodies. I hope this study will help bring this point home.