High-intensity interval training (HIIT) is a popular fitness trend in gyms across North America. That’s not surprising because this unique form of exercise has been shown to aid in weight loss and provide an array of health benefits in a fraction of the time it would take to complete a traditional moderate-intensity workout. (12) But you don’t need to be an avid athlete to take advantage of the health and wellness benefits of HIIT. In fact, adding a HIIT routine to your existing exercise program not only burns calories with a minimal time commitment, it might also help you live longer! (32)
What is HIIT?
In a nutshell, HIIT alternates short periods of explosive bursts of exercise with less intense recovery periods. Workouts can last from less than 10 minutes to 30 minutes total, including the warm up, recovery time between exercise intervals, and cool down. (9) According to the American College of Sports Medicine, the intense bursts of activity are performed at 80 to 95% of your maximal heart rate (the number of times your heart beats in a minute) and are alternated with less intense activity performed at 40 to 50% of your maximal heart rate. This combined work/rest interval is commonly repeated six to ten times. (28)
Along with shaving a significant amount of time off your workout, HIIT can be customized to an individual’s favorite type of activity. What’s more, it can also be modified for those with disabilities or existing health conditions. (4)
Did you know? The U.S. Department of Health and Human Services recommends that adults get between 150 and 300 minutes of moderate-intensity exercise per week. However, you can cut that time commitment in half by opting for high-intensity workouts instead. (4)
Benefits of HIIT and interval training
The physiological benefits of HIIT training go far beyond its time-saving perks. Studies show that routinely alternating intense physical activity with “rest” periods can provide a variety of health benefits. According to a paper in the journal Applied Physiology, Nutrition, and Metabolism, completing just three HIIT sessions per week improves aerobic capacity, skeletal muscle oxidative capacity, exercise tolerance, and markers of disease risk. (9)
1. Cardiovascular benefits
Exercise has a well-earned reputation for enhancing cardiovascular health, and HIIT is no exception. In one study of 65 patients with hypertension, researchers found that while both continuous exercise and HIIT helped with blood pressure control, only HIIT reduced arterial stiffness—a predictor of cardiovascular disease in people with high blood pressure. (10) Another 12-week study involving 63 testicular cancer survivors found that adding supervised HIIT workouts to their usual care improved arterial thickness and stiffness, inflammation, and low-density lipoprotein (“bad cholesterol”) levels. These actions led to a 20% reduction in modifiable cardiovascular risk factors. (1) In other research, HIIT was shown to enhance circulation and reduce oxidative damage, further supporting healthy arteries. (26)
2. Cellular benefits
A recent study that appeared in the journal Cell Metabolism found that high-intensity interval training caused cells to make more proteins for their energy-producing mitochondria and their protein-building ribosomes, reducing aging at the cellular level. The trial, which involved two groups—those aged 18 to 30 and those aged 65 to 80—looked at the impact HIIT had on cells. While the younger volunteers saw an impressive 49% increase in mitochondrial capacity when participating in the HIIT workout, the older volunteers experienced an even more dramatic 69% increase. (27)
3. Mental health benefits
Numerous studies have linked exercise to better cognition and well-being, especially in older adults. (19)(25) HIIT may be especially beneficial. One clinical trial published in the journal Brain Sciences found that the mental health benefits of HIIT included improved executive function, reaction time, and cognitive flexibility in a group of adults in their 60s. (21) However, seniors aren’t the only people who experience these brain benefits. Other studies suggest that interval training can improve cognition in all ages, even children. (20)(22)
HIIT may also be able to enhance mood by easing anxiety and warding off depression. One study involving 33 people with generalized anxiety disorder found that HIIT was significantly more effective for relieving anxiety than lower-intensity workouts. (24) Another clinical trial discovered that HIIT improved depressive symptoms in a group of healthy women. (34) These mood-boosting improvements may be due to HIIT’s ability to increase glutamate and GABA—two neurotransmitters that regulate chemical messaging in the brain. (17) HIIT can also improve mood by increasing BDNF, a protein involved in regulating brain function and mood. (8)
4. Metabolic benefits
Preventing metabolic syndrome and type 2 diabetes with exercise involves improving insulin sensitivity and controlling blood sugar. (15) HIIT is especially effective for enhancing both, especially in people who are at a higher risk for type 2 diabetes. One review of 17 studies found that 12 weeks of HIIT significantly improved insulin sensitivity and fasting glucose levels. (14) Another 12-week training study involving patients with type 2 diabetes reported that high-intensity walking intervals were more beneficial than continuous moderate exercise for controlling blood sugar. (13) These studies suggest that adding a HIIT workout to a healthy lifestyle may help prevent metabolic problems and help those with type 2 diabetes manage their condition.
5. Respiratory benefits
Studies show that applying HIIT to aerobic activities like running or cycling can improve lung capacity, lung function, and VO2 max (the amount of oxygen used during exercise). (3)(2)(23) According to one meta-analysis, adding just two HIIT sessions per week improved VO2 max and overall cardiorespiratory fitness in older adults. (36) Even those with COPD or other pulmonary conditions can improve their lung function and exercise capacity by incorporating modified HIIT sessions into their wellness plan. (30)
6. Weight loss benefits
Weight loss is one of the top reasons many people start working out. Studies suggest that HIIT can burn up to 30% more calories in less time compared to other forms of exercise. (35)(6) HIIT can also target fat—especially abdominal and visceral fat. (5)(18) A 12-week randomized controlled trial involving 46 overweight young women found that those participating in HIIT workouts consisting of four minutes of cycling at 90% VO2 max with three minutes of rest experienced a marked reduction in total fat, abdominal fat, and visceral fat. (33) Another 12-week trial, this time involving overweight young men, found that participating in a 20-minute HIIT session three times per week resulted in a loss of 4.4 lbs and a 17% reduction in visceral fat. (11)
Did you know? You keep burning calories after your HIIT workout at a higher rate than you would after a continuous exertion workout. (31)
How to create an effective HIIT workout
Because you can customize your HIIT routine based on your exercise preference, fitness level, and any underlying medical conditions, there’s no one-size-fits-all way to add this time-efficient form of exercise into your routine. That said, there are two common ways to incorporate HIIT into your fitness regimen—cardio-only or a dynamic body weight workout.
Cardio-only HIIT workout
During a cardio-only workout, you would exercise at a high intensity for a set period of time (e.g., 30 seconds to four minutes) before switching to a lower-intensity activity for the same amount of time or more. Good candidates for high-intensity activities include:
- Cycling on a stationary bike
- Rowing on a stationary rowing machine
- Running on a treadmill or outdoors
- Speed-walking outdoors
Dynamic body weight HIIT workout
A dynamic HIIT workout uses your bodyweight to quickly work your entire body by combining strength and cardio. Typically, you would do a two-minute warm-up (e.g., jogging, high knees, or jumping rope) before diving into a circuit of several continuous bodyweight exercises followed by a 30-second rest period. You would then repeat the process one or more times. For example:
- Burpees: 20 seconds
- Squat to high kick: 20 seconds
- Mountain climbers: 20 seconds
- Rest: 30 seconds
How often can you do a HIIT workout?
Recent findings published in the journal Cell Metabolism noted that participating in a HIIT cycling routine two to three times per week can improve fitness levels and increase the production of mitochondria—the energy factories that power cells. But when the study participants began doing the HIIT workouts daily, these gains started to deteriorate. (7) Excessive HIIT sessions may also increase the risk of injury. (29)
Download a handout on high-intensity interval training to learn more.
The bottom line
HIIT can work well for people who are short on time or for those wanting to change up their workouts. Adding HIIT to your exercise regimen can improve your health from head to toe. But, as with any type of exercise, it’s important to check with your healthcare practitioner before starting HIIT, especially if you have an existing medical condition.
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