In parts one and two of this series on the benefits of strength training over 40, we talked about preventing frailty and osteoporosis. But did you know lifting weights also helps protect your heart and your brain?!
As discussed in the post on sarcopenia, in the absence of taking any preventive steps, we begin losing muscle tissue in our 30s. By the time we get into our 50s, we may be losing as much as 2% of our muscle every year. And obviously, not having muscle has dire implications for our ability to move around, conduct the activities of daily living, and stay independent.
But muscle loss–and even more importantly, the replacement in the body of muscle tissue with fat tissue–has a more malevolent consequence. Sarcopenia tracks closely with the development of insulin resistance, which plays a pivotal role in diseases like diabetes, cardiovascular disease, dementia, fatty liver disease, and even cancer. These illnesses cause untold suffering in old age and usually lead to premature death.
Insulin resistance 101
If you or anyone close to you is diabetic, you already know that your pancreas produces a hormone called insulin that processes glucose (the simplest form of sugar).
Glucose fuels your body. Every cell requires it. In fact, without glucose, your brain would stop functioning and you’d die within a matter of minutes.
Digestion breaks down much of the food you eat into glucose. Your body naturally tries to keep blood sugar at a low, steady level, so when your pancreas perceives rising blood sugar levels, it releases insulin, which in turn signals your cells to allow the glucose through their outer membrane. At that point the glucose becomes available to the mitochondria within the cell, which serve their function as cellular power plants and convert the glucose into energy.
Insulin resistance is essentially what it sounds like: the cells become increasingly deaf to the signals that insulin is trying to send and stop allowing glucose to enter through their membranes, like a petulant teenager slamming the door of their room and locking everyone out.
The pancreas in turn tries to compensate for the unresponsive cells by working harder and harder to generate more insulin. The cells get more resistant. Ultimately the pancreas just can’t pick up that slack any more; instead of getting used properly, glucose remains circulating in the bloodstream.
The Legion of Doom
This vicious cycle often results in the formation of Type 2 diabetes. But high blood sugar causes damage long before it becomes uncontrolled and potentially fatal. Consistently high blood sugar causes chronic inflammation that damages blood vessels and organs throughout the body.
High blood sugar rarely travels alone. Most of the time, it attracts and then runs in a pack with four other villains. Together, these comprise metabolic syndrome, or Met-S:
- high blood sugar
- high blood pressure
- abdominal or “belly” fat (which indicates visceral fat, or fat around the organs)
- high triglycerides
- low HDL (“good”) cholesterol
Met-S drastically increases the risk of heart disease, stroke, liver disease, diabetes and dementia. The underlying mechanisms that cause it are extremely complex and there are many contributing factors. But insulin resistance appears to play a key role.
The Insulin-Muscle Connection
Why are we talking about high blood sugar and liver disease and diabetes in a blog about strength training? Aren’t diet and cardiovascular exercise the primary factors in preventing obesity and staying healthy?
Well, yes. And no.
Here’s what most people don’t know: Your muscles handle the vast majority—80%—of glucose processing in your body.
As mentioned earlier, when your pancreas responds to the presence of glucose by releasing insulin, the insulin in turn triggers receptors in your muscle tissue (in an individual with proper insulin sensitivity) to allow the glucose into the muscle cells, which either use it immediately or store it short-term to tap for energy later.
When muscles use up their stored energy, they need to seek more in the form of glucose. The harder your muscles are working, and the more muscle tissue you have, the more glucose gets absorbed, preventing insulin resistance.
Conversely, when you LOSE muscle tissue, you lose the primary mechanism that your body has to control its glucose levels and prevent those sugar molecules from circulating freely in the blood.
Muscle and fat are glands
It’s also been increasingly understood by scientists in recent years that muscle doesn’t only respond to signals like insulin–it actually produces its own signaling hormones, which in turn are sensed by and affect the way some of our body’s fat (adipose) cells behave.
Not only that, adipose tissue also releases molecules. These interfere with insulin processing, make muscle-building more difficult, and cause systemic inflammation and faulty processing of lipids in the liver.
In other words, both muscle and fat cells actually act like endocrine glands in our bodies, and their relationship contributes a great deal to our health or lack thereof as we age. People with a high fat-to-muscle ratio are more likely to have Met-S and its component health problems and outcomes. This seems to be particularly true of women.
As they age, some people who do not engage in physical activity tend to develop sarcopenic obesity, which means that muscle tissue gets replaced by adipose tissue.
This is a double whammy. When you lose muscle, your body’s insulin processing abilities take a hit. And, if you’re also replacing the muscle with fat, the adipose tissue itself interferes with insulin processing.
However, while the two often go together, insulin resistance does NOT require obesity to exist. Lean people often think they’re safe from the diseases of aging, but simply not having enough muscle, alone, can exacerbate insulin resistance. In fact, one study found that arm circumference, as an indicator of muscle mass, was actually a good predictor of insulin resistance in non-obese elderly adults.
Strength training to the rescue
Metabolism and insulin processing are highly complex. The good news is that exercise in general offers a simple, inexpensive and very well-proven way to fight chronic high blood sugar and insulin resistance. And strength training is an extremely effective component of that, especially in combination with aerobic exercise and/or interval training.
Lifting weights doesn’t only give you more muscle–it actually also increases the number and activity of molecules in the muscles that are responsible for glucose transport. This means the muscles are better able to take up glucose from the blood, leading to lower blood sugar levels.
In other words, having more muscle not only gives your body more rooms into which to invite glucose, it also unlocks the doors to those rooms so the glucose can move in more easily.
In addition to having a direct beneficial impact on insulin processing, strength training also helps prevent Met-S, cardiovascular disease and dementia. It can lower high blood pressure, increase HDL, encourage your body to burn fat more efficiently, and even help ward off Alzheimer’s disease.
With so many great reasons to strength train, what are you waiting for? It’s a no-brainer. If you’re not already lifting heavy things, make a plan today to get started!