digest
As you sit there in your chair, you are expending a rough amount of energy, somewhere around a calorie per minute. When we exercise, we can increase this by about 20 or 30 fold. As you sit there, your muscle contributes about 30% of your energy. During exercise, it contributes about 90% of your energy, so it becomes the major site where we burn carbohydrate and fat. When we eat a meal, about 80% of the energy that is ingested in that meal is distributed to the muscle. In other words, when muscle begins to fail or when we develop problems with our muscle, it is not surprising that we develop a range of diseases associated with that.
There are two things that have happened in modern science that have unintended consequences for the way that muscle functions. The first is automation. In modern life, we are predisposed to being physically inactive. We spend a large amount of our time in a sitting position. Even if we do our half hour of purposeful exercise first thing in the morning, we spend about 90% of the next 15 and a half hours of waking time in a seated position. One of the problems with sitting is that it is an independent risk factor for a majority of diseases. Even if you exercise first thing in the morning, last thing at night, or whenever you exercise during the day, if you do it in a single bout and spend the rest of your day sitting, you might be classified as an active couch potato. Potatoes do not have much use for muscles. If you look at someone like this, and we tend to associate inactivity and an inappropriate diet with an increase in size, in actual fact the muscles of individuals such as this guy on the couch are getting smaller and smaller and working less and less.
The second major thing that modern science has delivered is medication, and as a result we are living longer and longer. We have a worldwide aging, or grey, population. In the pie charts, the yellow segment represents the numbers of people who are over 65. At current projections, sometime after the year 2050, the number of people who are greater than 65 years of age will exceed the number of people who are less than 15 years of age, for the first time in human history. However, with aging and extended lifespans due to improvements in our medication, unfortunately this is associated with chronic diseases. In data from US adults aged over 65, the current numbers would suggest that 92.2% of those individuals have one or more chronic diseases. So although we are living longer, we might not necessarily be living healthier. Chronic diseases in this case were defined as the usual ones we tend to hear about: hypertension, chronic heart disease, stroke, cancer, and so forth. But there is one disease that is not mentioned here that I want to talk about more: sarcopenia.
Sarcopenia is defined as the age-related wasting of muscle. The word comes from Greek, which means a poverty of flesh, but it also means a poverty of strength. We lose muscle mass and we lose strength as we age. This is inescapable. It is a fact that happens after about the age of 30: we lose three to eight percent of our muscle every decade. Keep that number in mind, because I am going to come back to it. On the right-hand side of the second figure, you see the appearance of the thigh muscle of an individual, a cross-section of their thigh. What you can see is that in an elderly individual, they have lost a large proportion of their muscle mass. The white color there indicates adipose tissue, or fat, so the muscle has shrunk. Beneath that is a 74-year-old athlete who has trained their whole life and has managed to maintain their muscle mass, despite the inescapable fact that we would lose muscle throughout our life.
You might wonder what the prevalence of sarcopenia is, and whether it is just a disease this guy is really interested in. At the moment, in over-65s, the prevalence is about 20%. This is data from the US. In people over the age of 85, greater than half of individuals have sarcopenia. When you lose strength and power in your muscles, these are greatly associated with balance. If you lose your capacity to balance, you are more predisposed to falls and fractures. This loss of muscle mass is a strong risk factor for frailty syndromes, loss of independence, and general ill health as we age. We do not have any figures for Ireland, but we do know there is another part to this story, which is disease-related malnutrition. This might surprise you, but in Ireland at any one time there are 140,000 people suffering from disease-related malnutrition. This costs, in direct costs, about 1.5 billion euro to the exchequer. You might ask what kind of disease this is. That is more than the direct cost of obesity. This is an invisible type of disease, disease-related malnutrition, very strongly associated with age-related muscle wasting.
So why is strength important? I mentioned the incidence of frailty and loss of independence. If we look at individuals who are either over 60 or under 60 and we look at their whole-body strength, three colors represent weak individuals, average individuals, and strong individuals. If you look at the two red bars, you see that as we age, the over-60s have a four times elevated death rate compared to the under-60s. That makes sense: if we are older, we are more likely to die. However, on the right-hand side, if you compare the green to the red, the stronger you are, the lower your risk. The strongest third of the population have half the death rate of those who are weakest. In other words, if you preserve your muscle mass, you have a greater chance of living that little bit longer.
Why would that effect be so obvious, and why would it be relevant to something like cancer? Are there other diseases that sarcopenia or muscle wasting relates to? There are. All of the diseases listed on this slide coincide with muscle wasting. When each of those diseases manifests itself, it is also associated with the loss of muscle mass and therefore a loss of independence. The one I want to focus on is immobilization and bed rest. If you take young healthy males in their 20s, a student population, you have probably heard of the 10,000 steps you need to do in a given day to be healthy. If you take people who are making those 10,000 steps and you reduce their activity by making them take elevators, take escalators, push them around in wheelchairs, and make them sit a lot more, and you reduce their number of steps to 2,000, they lose about 5% of their muscle mass in the space of 14 days. I said that usually we lose about 3 to 8% per decade over the age of 30, so these individuals lose 5% of their muscle mass within 14 days. If an elderly person over the age of 70 is bedridden for 10 days, they lose 10% of their muscle mass. In other words, depending on the situation, in as little as two weeks you can lose the equivalent muscle mass of what would take a decade to lose. We want to avoid these things. We want to avoid immobilization, we want to stay active, and we want to avoid bed rest where possible.
So how should we do this? Typically we are told that we need to get out and walk more, and do half an hour of accumulated activity on five different days of the week. I am going to tell you that this is probably not enough. The principle of specificity in exercise training is that the body adapts specifically to the imposed demands. If we want to get bigger, improve our strength, and improve our muscles, we have to lift weights. Going out for a walk is not going to make you stronger. In fact, there is some evidence that lifelong endurance, aerobic, or cardio exercisers are predisposed to losing muscle mass compared to those who do strength training. The other interesting thing is that for diseases like diabetes and obesity, the most recent evidence suggests that combined endurance and aerobic exercise works. You should not just do one or the other; there should be a combination. A second principle in exercise training is the principle of progressive overload. This is Milo the wrestler, a famous Greek wrestler from two and a half thousand years ago. The story goes that to develop his strength as he grew, he carried a calf around from a young age. He carried it every day, and as the bull got bigger, he got stronger. I do not know if this is true, but the point is that each day he pushed himself a little bit harder, and his body adapted accordingly. That is an important principle of the way we exercise.
The question then is: if an adult is old, in this case over 85 years of age, can we exercise-train them and actually make improvements? On the left-hand side, you see the pre-intervention cross-sectional area. In this particular individual, the muscle in their thigh, the quadriceps, has increased by about 44%. On the right-hand side, you see their improvement in strength, which has improved by about 50%. That was after 12 weeks of training focused on the quad muscles in 85-year-old individuals. In this case, muscle wasting could be reversed. In other words, we have reversed the aging process.
So do we have to go to a gym? Do we have to invest in expensive equipment? Something we are excited about at UCD at the moment is using bodyweight exercises. These are exercises where you use your own body weight in space to provide resistance against your muscles. I will give you two small studies we have done. We took young college-age males, some obese and overweight, and trained them for six weeks, three days a week, half an hour each day. All they did were bodyweight-type exercises, with no equipment. After six weeks, we saw about a 3% improvement in muscle mass, particularly in the legs, and we had the holy grail: they lost a small bit of fat as well. We also studied older adults starting at age 55, with a mean age of about 63. After 12 weeks of bodyweight-only exercise three times a week, we saw about a 3% improvement in their muscle mass. Improving muscle mass is one thing, but these exercises are very similar to things we do in everyday activities. We lift things above our head, we get up off the ground, we get up out of chairs. These are what we call activities of daily living. One of the major predictors of loss of independence is when an older adult can no longer do these activities of daily living. We are now excited to look at these bodyweight exercises and how they might improve the overall health and functional capacity of older adults.
The last thing I will say is that in the case of sarcopenia or muscle wasting, you do not just wake up one day with this situation. It is a continuum that progresses over time. I was talking about bodyweight exercises being able to increase muscle mass, but if we can delay the aging process, if we just maintain muscle mass rather than having to improve it, that in itself will have benefits for overall health. My simple message is this: we need to prescribe exercise like we prescribe medicine. We should not give everyone the same medicine; we should treat the individual and treat the condition. Going out and doing 30 minutes of walking every day might not cut it for people who have age-related muscle wasting. What I would say is: use it or lose it, because muscle matters, and only the strong survive. Thank you.