Reduce blood sugar
Type 2 diabetes reflects excess blood sugar over long periods of time. Increased physical activity reduces the risk of developing type 2 diabetes and improves its management. Physical activity increases muscle demand for blood sugar thereby reducing blood sugar levels. Researchers in Canada tested whether high-intensity interval training (HIIT) could reduce excess blood sugar and increase muscle mitochondrial activity in 8 patients with overweight or obesity (average age 63 years, body-mass index 32) with type 2 diabetes. The volunteers participated in six HIIT sessions with 10 bouts of cycling for 60 seconds each at 90 percent of maximum heart rate interspersed with 60 seconds of rest over two weeks. Glucose responses were measured with continuous glucose monitoring devices before and after training. Average glucose concentration declined significantly after (119 mg/dL) compared to before (138 mg/dL) training. (By way of comparison, glucose levels of 100 mg/dL signify type 2 diabetes.) Areas under the glucose curves (measures of total amount of glucose) during three-hours after breakfast, lunch, and dinner also declined significantly after compared to before training. Muscle oxidative capacity (measured as citrate synthase activity) and protein concentrations both increased significantly after training. HIIT rapidly improved glucose control and improved markers of muscle function in type 2 diabetic patients, presumably improving diabetes management.
Reduce post-meal blood sugar
Recent research indicates that short bouts of high-intensity exercise (also known as interval training) often lead to superior physiological and health outcomes compared to long periods of moderate-intensity exercise. Exercise either pre- or post-meal can reduce subsequent spikes in blood glucose levels. Such spikes are associated with oxidative stress and inflammation. Only about 10 percent of Americans get the recommended minimum levels of weekly exercise. “Lack of time” is cited as a major barrier to getting sufficient exercise. Thus, short periods of high-intensity exercise might be more palatable to Americans, as well as more beneficial, than long periods of moderate-intensity exercise.
Researchers in New Zealand investigated whether short periods of high-intensity walking and/or resistance training before the main daily meals would provide better blood glucose control compared to post-evening meal moderate-intensity exercise. Nine participants were randomized to three exercise regimens each undertaken in random order. Regime 1 featured 30 minutes of continuous walking on a treadmill at 60% maximum heart rate 30 minutes before an evening meal. Regimen 2 involved six one-minute intense walks (90 percent of maximum heart rate) on a treadmill interspersed with one-minute slow walks completed 30 minutes before each main daily meal. Regimen 3 included three one-minute intense walks (90 percent of maximum heart rate) on a treadmill interspersed with one-minute slow walks and three one-minute intense resistance band exercise interspersed with one-minute slow walks, all completed 30 minutes before each main daily meal. The energy expenditures of the three exercise regimens were equal. The researchers found that, compared to continuous, moderate-intensity exercise, Regimens 2 and 3 reduced three-hour blood glucose following breakfast and dinner but not lunch. Regimens 2 and 3 also reduced 24-hour blood glucose compared to continuous, moderate-intensity exercise. Thus, short doses of high-intensity exercise provided better blood glucose control than long doses of moderate-intensity exercise. The prospect of getting more benefit from shorter but more intense exercise might motivate more Americans to take up interval training to reduce their risk of type 2 diabetes and otherwise improve their health and well-being.
Better cardio-metabolic health
Smaller volumes of HIIT produce greater cardiorespiratory fitness than greater volumes of continuous, moderate-intensity training. Does this hold for persons with cardiometabolic diseases such as coronary heart disease, hypertension, and the metabolic syndrome? Results from 19 studies in a systematic review and meta-analysis of published studies showed that it does. Meta-analysis revealed that HIIT increased peak VO2 by 3.0 ml O2 per kg body weight per minute more after HIIT training than after continuous, moderate-intensity training. HIIT nearly doubled the increase in peak VO2 compared to continuous, moderate-intensity training (19.4 percent vs. 10.3 percent). HIIT led to greater gains on other adaptations compared to continuous, moderate-intensity training, including lower systolic and diastolic blood pressure, greater HDL-cholesterol, lower triglycerides, greater cardiac function, and quality of life, among others. When used with appropriate screening and communication, HIIT can be a safe and effective exercise option for patients with chronic diseases, probably including type 2 diabetes.
Is HIIT safe for persons with type 2 diabetes?
Canadian scientists reviewed the effectiveness and safety of low volume, high-intensity interval training (HIIT) for people with type 2 diabetes. The many variants of low-volume HIIT limit specific findings about the relative effects of continuous, moderate exercise versus low-volume HIIT to better manage blood sugar. Nevertheless, the reviewers conclude that low-volume HIIT at intensities of about 70-95 percent of maximal aerobic capacity safely provide similar or greater cardiovascular and blood sugar management benefits in less time than more traditional continuous, moderate-intensity exercise. One meta-analysis found that cardiorespiratory fitness from HIIT doubled that from moderate-intensity training. Regardless of the superior benefits of HIIT, the American Diabetes Association still recommends the standard 150 minutes per week of moderate to vigorous exercise for persons with type 2 diabetes. A word of caution: Sedentary people with type 2 diabetes should consult a physician before embarking on a HIIT exercise program.
The 5x1 and 7x1 HIIT protocols
Researchers in Europe developed a practical, supervised high-intensity interval training protocol that would lessen cardio-metabolic risk factors for type 2 diabetes. The first iteration (7x1) included 46 volunteers with overweight or obesity with an average of 37 years. The 7x1 protocol included three weekly sessions of 7 bouts of cycling each for 1 minute at an intensity sufficient to elicit VO2max, interspersed with 1 minute of rest, for 6 weeks. Two minutes of warm-up preceded each exercise session. While the program led to a 6.2 percent increase in VO2 max, it did not sufficiently assess inter-individual variability.
The second iteration (5x1) included 164 participants with an average age of 36 years. This protocol included 5 bouts of cycling each for 1 minute starting at 85 percent of the work needed to elicit VO2 max (increasing by 10 percent in each subsequent session), interspersed with 90 seconds of rest, for 6 weeks. This program created an average 10.0 percent increase in VO2max. In addition, the type 2 diabetes markers fasting insulin concentration and HOMAR-IR (a measure of insulin resistance) decreased significantly from pre- to post-training. Interestingly, at three weeks following the end of training, HOMAR-IR maintained its immediate post-training level. The 5x1 protocol matched the efficacy of a 30-week program of moderate-intensity exercise in terms of VO2 max, mean blood pressure, and HOMAR-IL.
Meta-analyses have shown that HIIT can improve the metabolic status of patients with type 2 diabetes. A more recent systematic review and meta-analysis included 20 studies that compared the effectiveness of high-intensity interval training (HIIT) to moderate-intensity continuous training (MICT) or a different control for patients with type 2 diabetes. The outcomes included increase in VO2 max and decrease in HbA1c (the gold standard for measuring blood glucose). HIIT increased VO2 max significantly more than the control (5.1 ml O2/kg body weight-minute) and significantly more than MICT (1.9 ml O2/kg body weight-minute). HIIT lowered HbA1c levels significantly more than the control (0.8 percentage points) and reduced HbA1c levels by 0.35 percentage points, significantly not different from MICT. HIIT protocols that included moderate to long work intervals, moderate to high volume, and moderate to long training periods showed the greatest increase in VO2 max. To reduce HbA1c levels, HIIT protocols with short intervals, moderate volume, and long training periods were most effective. Overall, HIIT can provide an effective alternative to more traditional moderate-intensity, continuous exercise
What to do
If you've been diagnosed with pre-diabetes or type 2 diabetes, you need to take steps (literally and figuratively) control your blood sugar. Apart from eating better, which is the biggest deal of all, you also need to get plenty of physical activity. HIIT offers a highly time-efficient way to help keep your blood sugar in a healthy range. The highly engaging book, The One-Minute Workout, by noted researcher Martin Gibala, includes details of several versions HIIT, at least one of which will probably suit you.
