HIIT has surged in popularity as an effective, time-efficient way to exercise. Here’s why HIIT has taken the fitness world by storm and how your body can benefit.

Health experts worldwide cannot praise the power of exercise for its impact on health enough, yet less than 5% of us exercise for 30 minutes every day, and only 53.3% of us get the 150 minutes of aerobic physical activity we should be getting every week.

Topping the list of reasons for not getting enough physical activity is the simple fact that so many of us lead busy, bustling lives and rarely have the time. So, what to do when we still want to reap all the heart-pumping rewards of a good workout but in the least amount of time possible? The solution just might be HIIT, also known as high-intensity interval training.

What is HIIT training?

A HIIT routine blends short spurts of intense exercise with periods of two to three minutes of active recovery or lower-intensity exercise, often involving a combination of resistance training with aerobic activity like cycling and running. Most HIIT workouts aim to reach 90 to 100% of aerobic capacity during intense periods and recovery intervals of 2 to 3 minutes around 40% HRR (heart rate recovery). Aerobic capacity or VO2 max is the maximum amount of oxygen your body can use at one time during an intense exercise.  HRR is how quickly your heart returns to normal after you stop exercising. HIIT has attracted the attention of the fitness world as a time-efficient option that can generate as many, and in some cases, even more health benefits than moderate, longer aerobic workouts.

Science-backed ways HIIT can do your body good

1. HIIT may improve cardiorespiratory fitness. A 2018 study looked at the maximal oxygen consumption (VO2) of 49 healthy, active women aged 30 years old before and after 8 weeks of four bouts of 4-minute high-intensity cycling, performed at 50-60% peak heart rate. After the trial, the researchers saw a slight 14.5 ± 22.9% improvement in the subjects’ VO2. This improvement increases cardiorespiratory fitness.

2. HIIT can enhance insulin sensitivity. Insulin sensitivity alludes to how sensitive, or receptive, the body’s cells are in response to insulin. High insulin sensitivity allows for a reduction in blood sugar because the body’s cells can use blood glucose more effectively. People with lower insulin sensitivity, called insulin resistance, have a higher risk of developing type 2 diabetes. Taking insulin-sensitizing medication, losing weight, and exercising can all improve insulin sensitivity.

How might HIIT impact insulin sensitivity? One study measured the insulin resistance of 40 adult women - some with higher insulin resistance and some with lower insulin resistance - before and after performing 8-12 60 second high-intensity cycling intervals with 120 seconds of rest in between, three times a week for 10 weeks. After the study, the group with higher insulin resistance saw a significant reduction in fasting insulin by 26.5% and fasting glucose by 8.8%. And as a bonus, both groups saw a drop in waist circumference, and the lower insulin resistant group also experienced a reduction in systolic blood pressure.

Can HIIT benefit persons living with diabetes?

Exercise training is one of the most impactful ways to improve health, and for persons with diabetes, this is no exception. In fact, the American Diabetes Association suggests that performing HIIT exercises regularly may be an especially beneficial, time-efficient therapy in managing diabetes by significantly improving glucose control, insulin sensitivity, and cardiovascular health. This is great news for those who are crunched for time during the week.

How much - or how little - HIIT time is required to see the effects? One study showed that 1-minute vigorous intensity exercises at 90% of maximal aerobic capacity repeated 10 times interspersed with 1-minute rest periods was enough to reduce 24-hour average blood glucose concentration by 18 mg/dL for subjects with type 2 diabetes. Diabetes is indicated when blood glucose measures above 126 mg/dL. These subjects saw their blood glucose measurements decrease from 136.8 mg/dL to 118.8 mg/dL. This beneficial effect was seen when HIIT was performed three times a week for just two weeks. This amounted to only about 30 minutes of activity per week.

If you are living with diabetes and are considering starting a HIIT routine, make sure to first consult with your healthcare provider to ensure that it is safe for you.

3. HIIT is an efficient way to burn fat. Overweight men who sprinted for 8 seconds and then rested for 12 seconds for a total of 20 minutes, 3 times per week for 12 weeks, saw a reduction of total fat mass by 4.4 lb and a 17% drop in visceral fat after 12 weeks. This matters because visceral fat is the fat found around the abdomen most associated with chronic disease.

4. HIIT can boost mental health. All exercise can go a long way in helping us maintain emotional balance, but exercising intensely is shown to be especially powerful in making us feel good. People with depression and anxiety appear to especially benefit from HIIT exercise. For example, a HIIT protocol made up of 25 intervals of 30 seconds of work at 80% VO2max followed by 30 seconds of rest performed three times a week for 4 weeks is shown to lead to a reduction in depression severity for people with depression. And when 33 subjects with generalized anxiety disorder performed either HIIT training or a lower-intensity stretching protocol, the group that trained with HIIT saw twice the reduction in their anxiety symptoms than their stretching counterparts after just 12 days.

A word about HIIT before you get started

If you are brand new or not very experienced with exercise, whether you have diabetes or not, it is always a good idea to first ask your primary care provider to make sure you do not have any underlying heart or other age-related conditions before starting a new HIIT routine. Remember to start small. It is often best to first build up your fitness level to prevent injury. Of course, any physical activity is great for your health, so keep moving your body whether intensely or not.


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