The research was performed by Dr. Jane Yardley as part of her PhD studies at the University of Ottawa, under the supervision of Dr. Glen Kenny from the University of Ottawa and Dr. Ronald Sigal from the University of Calgary. Twelve physically active people with type 1 diabetes were recruited to look at how resistance exercise affects blood glucose levels when combined with aerobic exercise, and to determine if the order in which they’re performed makes a difference.
Although exercise has been shown to improve life expectancy and to decrease the risk of diabetic complications in people with type 1 diabetes, little research has been conducted to show what kind of exercise is the safest and most effective. Currently, many people with type 1 diabetes do not exercise, for fear of hypoglycemia (low blood glucose), a frequent occurrence during sustained aerobic activity.
Meanwhile, limited studies suggest that resistance exercise (weightlifting) or a combination of aerobic and resistance exercise may provide a greater benefit to blood glucose control than does aerobic exercise. The immediate effects of combined aerobic and resistance training on blood glucose, both during and after workouts, for those with type 1 diabetes are essentially unknown.
Dr. Yardley’s research sheds new light on this complex topic. Participants exercised for 90 minutes on two separate occasions: one where they ran for 45 minutes before lifting weights, and the other where they did the weightlifting first. Blood samples were taken throughout each exercise session to monitor glucose levels, and participants wore continuous-glucose-monitoring units to measure blood glucose for 24 hours after both workouts.
Researchers found that when aerobic exercise was performed first, blood glucose levels dropped right away and didn’t recover until the 90-minute exercise session was almost over. Nine out of the 12 participants needed to take in extra carbohydrate during exercise to prevent hypoglycemia. By contrast, when the exercise was performed in the opposite order (resistance first), blood glucose levels started to drop only after more than an hour into the workout, and fewer participants needed extra carbohydrate to finish the session. While overnight hypoglycemia was infrequent in the study, incidents tended to be worse after the sessions where aerobic exercise was performed first.
“Increases in sugar intake and decreases in insulin dosage that type 1 diabetes patients make to avoid hypoglycemia during exercise can essentially undo several of the benefits of exercise. This study shows that there are other options, which may in fact allow those with diabetes to gain more from their exercise activities while still staying safe,” says Dr. Yardley.
The researchers emphasize that more research on different exercise intensities and durations must be conducted before precise training regimens are prescribed. Dr. Yardley stresses that “…several physical, psychological and environmental factors can influence blood glucose levels during an exercise session in people with type 1 diabetes. As a result, it is crucial to consistently monitor blood glucose levels.”
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