Study Reveals Potential Mechanism in Strength Training That Can Help Reduce Insulin Resistance
When rats’ muscles were activated and strengthened in the experiment, they expressed more of a certain protein linked to improved insulin sensitivity.
Animal research out of Japan strengthens the case that exercise can help control glucose (blood sugar) levels in type 2 diabetes.
Previous scientific literature, including an August 2016 review in Diabetes & Metabolism, had established that aerobic exercise and resistance, or strength, training expand the storage capacity for blood sugar in the muscle and improve insulin sensitivity, effectively reducing the negative health effects of type 2 diabetes.
The findings in the new study, published in the February 2018 edition of the American Journal of Physiology, go a step further, suggesting that resistance exercise mitigates indicators of type 2 diabetes by increasing the effects of a protein that regulates blood sugar absorption in the body.
How Glucose Is Absorbed and Used in the Body
The hormone insulin is critical in regulating blood sugar levels and energizing the body. When you eat food, your pancreas secretes insulin into your bloodstream to help transfer glucose (the body’s main source of energy) to your muscles, fat, and cells. In people without diabetes, this process works well, but in those with insulin resistance — the hallmark of type 2 diabetes — insulin is unable to effectively ferry glucose to those key locations, causing glucose to accumulate in the bloodstream and the body to continue releasing insulin in an attempt to catch up.
In type 2 diabetes, your muscles, fat, and cells can’t absorb the insulin despite that increased production. The result is high blood sugar (hyperglycemia), which can lead to serious complications, like nerve damage (neuropathy), heart disease, kidney damage (nephropathy), and eye damage (retinopathy).
When you have type 2 diabetes, everything from diet and stress levels to medication and sleep habits can affect your blood sugar levels. But researchers in the current study analyzed the role of another player in this arena: APPL1, a protein that regulates glucose absorption and can improve the body’s ability to use insulin.
How Researchers Studied the Role of APPL1 in Insulin Resistance
It’s been shown that exercise makes APPL1 more effective, but the reason why hasn’t been completely clear. To learn more, researchers in the current study analyzed the effects that resistance training had on APPL1 in rats. Resistance training — such as lifting weights or using resistance bands — forces skeletal muscles to contract, leading to increases in muscle mass.
The researchers took a group of rats with type 2 diabetes and a group of rats without type 2 diabetes, and used tiny needles to penetrate the animals’ skin to stimulate and strengthen their muscles. In using those needles (a method dubbed “percutaneous electrical stimulation”), the researchers emulated a form of resistance training called maximal isometric contractions. In an isometric contraction, the muscle is activated, but instead of being allowed to lengthen or shorten, it is held at a constant length. An isometric contraction occurs when you hold an object steady in front of you.
For three weeks, researchers emulated the resistance training and compared the changes of APPL1 expression and insulin resistance in both groups of rats. At the beginning of the study, the rats with diabetes had lower APPL1 expression and higher insulin resistance than the control group. After the resistance training, both factors improved for the exercising rats, suggesting the exercise could improve indicators of type 2 diabetes.
What the Study Suggests About Resistance Training and Blood Sugar Regulation
The research team identified four separate signaling pathways that became activated as a result of resistance training, which in turn increased expression of APPL1. “These results are suggestive of a mechanism for chronic resistance training–induced improvements in insulin sensitivity in skeletal muscles of rats with [type 2 diabetes],” the researchers wrote.
Although these findings support prior clinical research on the benefits of regular exercise in type 2 diabetes management, this study is valuable in its discovery that APPL1 may be a key regulator of insulin resistance in skeletal muscle, says Daniel Hackett, PhD, an exercise and sport science lecturer at the University of Sydney in Australia. Hackett is also a coauthor of the aforementioned review in Diabetes & Metabolism that explored the effects of regular exercise on insulin sensitivity in type 2 diabetes.
But still, humans and rats aren’t the same, so more research is needed, Hackett says. “You cannot be entirely confident that findings would be consistent in humans,” he points out, adding that the current study also didn’t explore specifics that would be relevant for humans to know, such as how much resistance training would be needed to increase APPL1 expression. It’s unlikely that people would do that sort of resistance training via electrical stimulation, Hackett explains.
Sheri Colberg, PhD, founder of the educational website Diabetes Motion and author of Diabetic Athlete’s Handbook, says the new findings help further illuminate the mechanism by which glucose uptake is facilitated into resting muscle. She also echoes Hackett, saying the findings would need to be repeated in humans to establish APPL1 as the exact protein that changes in response to resistance training over time.
Hackett says future research would furthermore need to build on this study and earlier papers to explore what type of resistance training is most effective in improving insulin resistance. “Findings from this study should encourage people with and at risk of type 2 diabetes to integrate regular resistance training into their lifestyles,” he says, noting that if you’re new to resistance training, it’s important to consult your doctor before adding the exercise to your routine.