The Effects of Exercise Intensity on Insulin Control
Reducing insulin resistance should be a goal for everyone. For athletes, better insulin sensitivity means better use of energy, and perhaps greater anabolism. For the average Joe, it means keeping diabetes and pre-diabetes at bay. It’s estimated that some 35% of Americans are pre-diabetic, meaning they are at substantial risk for developing type 2 diabetes. And of course for the diabetic, good insulin control means an amelioration of symptoms.
It’s fairly well known that cardio training can help improve insulin sensitivity. What’s not as well understood is what intensity the cardio training should be to yield the greatest benefit. In a study this month in the Journal of Strength and Conditioning, researchers wanted to determine the intensity of cardio that would best modulate insulin sensitivity.
The researchers speculated that greater intensity would yield better results. They noted that this effect had been shown in the past in poorly-controlled conditions. Specifically, they wanted to compare cardio intensities where the total calorie burn was the same for each level. While there was evidence that greater intensity would generate a more substantial effect on the insulin systems of the body, it wasn’t clear if this had to do with the rate of cardio or the work done.
They participants were healthy people in their early twenties who weren’t highly trained on a bike. Since an exercise bike was used for the test, the researchers didn’t want experience on a bike to interfere with the results. The subjects also didn’t have metabolic diseases. It’s important to note that the results pertain specifically to how insulin sensitivity and resistance is adjusted by exercise intensity in healthy individuals.
Ultimately, intensity didn’t seem to matter when it came to insulin sensitivity. The researchers used three levels of intensity, including hour-long, moderate training and up to five-minute intervals that pushed the aerobic system intensely, but there was no difference in insulin effectiveness for any of the groups. The middle intensity group, which trained vigorously for 45 minutes at a time, and the interval group did demonstrate an improvement in VO2 max.
The researchers demonstrated that in healthy people, exercise intensity probably doesn’t matter much when it comes to improving the body's insulin systems. The differences noted in other studies likely had more to do with how much total energy was being expended, which needs further study itself in the future.
Because VO2 max was improved in the two groups with higher levels of intensity, the researchers still recognized and recommended the value of intense aerobic exercise. However, if the goal is to improve insulin effectiveness - an important goal for any athlete - calorie expenditure may well matter more. Until this topic is further studied, it would make sense to spend some of your cardio time maximizing the total calorie expenditure.
1. CR Grieco, et. al., “Effect of intensity of aerobic training on insulin sensitivity/resistance in recreationally active adults,” Journal of Strength and Conditionining Research 27(8), 2013.
Photo courtesy of Shutterstock.