At Efficient Exercise, we use the term “Sarcopenia” when discussing why new clients should endeavor into resistance training. This is Latin for “poverty of the flesh,” which really means age and/or inactivity-related losses in muscle mass. This was thought to be a primary driver of things like osteoporosis and obesity, even associating the term “sarcopenic obesity.”
However, this implies a sufficiency issue: just have enough muscle mass and you’re insured against many of the future losses that come with simply having the muscle. However, this did not explain why people of varying levels of muscle mass were experiencing these symptoms with prolonged inactivity. This is a bit like how skinny people can be “obese” as far as visceral fat to lean body mass ratio. There’s a hormonal milieu that can only be accounted for through the lens of use rather than presence.
At EE, we’ve always focused on maintaining muscle mass through aging, but it’s become increasingly clear that what matters most about muscle is the use rather than the amount. It makes sense that the focus was on sufficient muscle mass, as we were unable to measure any element of the tissue that communicated with the rest of the body…they were merely motors. Now we understand that muscle is in fact our largest endocrine organ, releasing hormones and signaling agents called myokines that communicate with the rest of the body to set the thermostat, so to speak, regarding the importance of muscle tissue and how it should be treated by the rest of the body.
Let me explain.
Go back to my first paragraph and the term “sarcopenic obesity.” The literature on this topic is totally interesting and the first thing that jumps out is that both muscle and fat tissue are very active endocrine tissues. The second thing that stands out is that these endocrine actions are almost in direct opposition to each other, like colonies in competition for energy resources. This is different than the old “auto-regulation” model that the body would partition based on substrate and availability, like when the muscles were replete with nutrients, the fat was a dump for whatever was left. This is now turning out to be incorrect.
In this review of sarcopenic obesity, researchers lay out all of the signalling mechanisms that fat and muscle use to facilitate endocrine communication. If you wrote down all of the mediators and their effects in separate columns labeled “muscle” and “fat” you’d see that they’re in competition. Age seems to dictate which tissue has the competitive advantage. When you are young, muscle has the competitive advantage over adipose tissue and the advantage slowly shifts toward fat as the years go by, largely because you pass childbearing years and your Darwinian Fitness reduces (or “evolution stops giving a damn” to quote evolutionary biologist Michael Rose). As you lose muscle, the signalling from fat mass becomes greater, begetting more fat mass, increasing the signal further as muscle continues to whither and reduce their signalling.
So the signalling from fat mass is largely due to the volume of fat mass. However, it turns out that muscle signalling is not due to the presence of the tissue itself (a sufficiency), but rather from the use of said tissue. This means that is actually a reduction in muscle quality, which means less strength, than correlates more with aging than merely having enough muscle tissue. The term for this is dynapenia which literally means “poverty of power.” It is the loss of strength which reduces the quality of our contractions, which reduces the signalling for resources, which reduces the partitioning of nutrients to muscle tissue and increases the partitioning toward fat mass, which begets more fat mass. A recent literature review demonstrates that strength is lost more rapidly than mass as we age. Considering it’s the very strength that would, for example, help prevent a fall or maintain balance through aging, this fact of rapid loss is especially important.
Strength precedes the signal and the signal is in proportion to the use of said strength. If you’re using a high intensity of effort on a regular basis, you’ve set the stage to maintain your strength, muscle tissue, and tip the balance toward lean mass instead of fat mass as we age.