Short, High-Intensity Exercise Sessions Improve Insulin Production in Type 2 Diabetes

Short, functional-movement and resistance training workouts, called functional high-intensity training (F-HIT) may improve beta-cell function in adults with type 2 diabetes, according to a study recently published in the American Journal of Physiology—Endocrinology and Metabolism.

Researchers led by John P. Kirwan, PhD, of Cleveland Clinic, point out that previous research has shown that aerobic exercise leads to improvements in beta-cell function and insulin secretion. The findings of these studies, the authors write, appear to show “a response dichotomy to exercise in the [type 2 diabetes] population, specifically dependent on residual beta-cell secretory capacity.”

But these studies only looked at aerobic exercise training, and given the rise in popularity of F-HIT (programs like CrossFit), Kirwan and his team wanted to look at how those exercise regimens affect insulin production. “Adults with [type 2 diabetes] may find it difficult to adhere to a strict exercise regimen, citing ‘lack of time’ as one of the primary barriers. F-HIT programs like CrossFit may address this barrier by providing structure, supervision and accountability, with a minimal time commitment,” the researchers write.

The team examined how a six-week CrossFit F-HIT intervention would affect beta-cell function in 12 sedentary adults with type 2 diabetes. The participants trained three days a week, performing functional movements at high intensity in a variety of 10- to 20-minute sessions under the supervision of a certified CrossFit coach. Activities varied weekly and included one high-intensity session in which the participants exercised until they hit greater than 85 percent of their maximum target heart rate. The participants then completed an oral glucose test and anthropometric measures at baseline and following the intervention.

The researchers took body fat and mass measurements before and after the F-HIT program as well. The CrossFit trainer recorded the number of repetitions of sit-ups, squats, and rowing each volunteer completed on the second and last days of the exercise program to track exercise capacity and overall fitness.

“The mean Disposition Index (DI), a validated measure of beta-cell function, was significantly increased (PRE: 8.4±3.1, POST: 11.5±3.5, P=0.02) after the intervention. Insulin processing inefficiency in the beta-cell, expressed as the fasting proinsulin-to-insulin ratio, was also reduced (PRE: 2.40±0.37, POST: 1.78±0.30, P=0.04). Increased beta-cell function during the early-phase response to glucose correlated significantly with reductions in abdominal body fat (R2=0.56, P=0.005) and fasting plasma alkaline phosphatase (R2=0.55, P=0.006). Mean total body fat percentage decreased significantly (Δ: -1.17 0.30%, P=0.003), while lean body mass was preserved (Δ: +0.05±0.68kg, P=0.94),” the authors write.

The short-term F-HIT regimen showed significant increases in beta-cell and liver function and exercise capacity. The volunteers also lost weight and body fat percentage through F-HIT exercise. These factors can improve insulin sensitivity and blood glucose levels. “Here we show that exercise at high intensity for as little as 10 to 20 minutes per day, three days a week for six weeks improves beta-cell function in adults with [type 2 diabetes],” the researchers write.