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There are several age-related conditions that are etched firmly in the public consciousness, such as diabetes, dementia, heart disease, cancer, osteoarthritis, to name but a few. But what about sarcopenia?

While it may not be an instantly familiar condition, its effects are easily recognizable in older adults: muscle loss, leading to declining strength, frailty and potential injury.

It is primarily caused by anabolic resistance, which impairs the ability of muscle to build proteins in response to feeding.

An 51ÁÔÆæÈë¿Ústudy, published in , has sought to find out the different causes behind anabolic resistance. The senior corresponding author of the study, Dave Clarke, associate professor, Department of Biomedical Physiology and Kinesiology, explains the findings.

What is anabolic resistance?

As a younger adult, when you consume protein from food, it gets digested into amino acids and enters the bloodstream where tissues take it up and use it to build proteins.

Skeletal muscles are a major destination for amino acids, which incorporate them through a process called muscle protein synthesis. Interestingly, muscle size is tied to the amount of protein in a muscle.

For those who pursue resistance training, prior resistance exercise primes the muscle cells to take in more amino acids and synthesize more protein. This leads to more muscle protein and muscle growth than through feeding alone.

As we age, our bodies develop a resistance to that process, which is known as anabolic resistance. Typically, muscle mass begins to noticeably decline around 30-40 years of age and accelerates in later life.

The consequences can be far-reaching for some people. When we lose muscle mass, we lose strength. When we lose strength, we can lose function and independence. The risk of suffering a fall goes up, possibly leading to hospitalization.

So sarcopenia is a very serious health-care issue, especially in an ageing population. Maybe it doesn’t get as much press as other age-related diseases, but I think we all know people who are ageing, who don’t move enough, who are getting more frail.  

What was the motivation behind your study?

We wanted to gain a better understanding of the factors that cause anabolic resistance, because several hypotheses exist about the possible causes of anabolic resistance, but there is no definitive answer.

Prior to this work, we developed a computer model of how muscle cells synthesize protein. We thought that this model could be productively applied to studying what happens when the process does not work properly.

There are also drug companies and research groups trying to develop therapies for sarcopenia. So we really want to inform this research. The model could also be adapted to study treatment strategies.

How did you carry out your research?

In my lab, we produce predictive computer models of exercise training adaptations to better understand fundamental biology, or in other words, how our bodies function at a basic level when we alter training routines.

Over time, as we refine our models, they may one day help us to design optimized training programs for individuals with specific goals.

For this study, we adapted our computer model, which is essentially a virtual muscle cell, to include the proposed age-related impairments in the process of muscle protein synthesis.

For example, we changed the model so that smaller quantities of amino acids reach the muscle cells after feeding, and reduced insulin signaling.

We systematically adjusted each factor alone and in combination, so we could determine which one(s) had the biggest negative effect on muscle growth.  

What did your study find?

We found that in all likelihood, anabolic resistance is not caused by one factor alone. When we made adjustments to factors in isolation, like amino acid delivery, we only saw modest effects on muscle protein levels.

But when we tested several factors acting simultaneously, the model predicted reduced muscle protein synthesis levels akin to those observed in older adults with anabolic resistance.

In other words, anabolic resistance appears to be a multifactorial problem.

What is the impact of your study?

The findings really emphasize the importance of looking at all the factors when seeking to treat anabolic resistance. Developing a drug that targets a single issue is unlikely to solve the problem.

Instead, successful treatments will likely have to target multiple issues. Our results suggest that targeting the muscles’ signaling system, which controls muscle protein synthesis, ought to be prioritized.

It is worth saying that prevention is better than the cure. Resistance training and eating sufficient protein are the best ways to prevent sarcopenia, and, if you have it already, the best ways to slow its progress.