By Aaron Boike, B.S. Kinesiology, American Council on Exercise Certified Trainer
High intensity interval training is all the rage in the fitness world and has been since the early 2000’s. Originally a technique used mainly by athletes to train in a way more specific to their sport, high intensity interval training (HIIT) is now commonly used by the general fitness population as a replacement for, or in addition to, traditional continuous aerobic training.
What is HIIT?
Interval training is simply the act of alternating periods of higher intensity and lower intensity during a workout. While it is a broad term, there are a few protocols that have become the most common to optimize fitness. The 1/1 ratio interval program is probably the most common and easiest to implement in a workout program. The 1/1 intervals can be done with periods as short as 20 seconds, and upwards of 2 minutes. However, the greatest benefits to metabolism and VO2 max (the rate at which your body can use oxygen during exercise) have been shown with shorter “max effort” intervals. The “Tabata” protocol is an example of a max effort protocol. Tabata has gained massive popularity in the past few years after research published in The Journal of Medicine and Sports Science showed an average of a 7 ml/kg/min increase in subjects V02 max after only six weeks. The Tabata protocol includes eight cycles of exercise with an interval ratio of 20 seconds of max effort work and 10 seconds of rest.
What Modes of Exercise Can be Used?
One of the great parts about doing a HIIT workout is that you can use any mode of exercise that is highly aerobic. This can range from biking, running, and elliptical machines; to highly aerobic resistance training exercises like burpees, mountain climbers, and speed squats. HIIT training has become a favorite of those who prefer non-traditional modes of cardiovascular exercise because it does not require you to use cardio machines and can be done just about anywhere with little to no equipment.
Is HIIT Safe?
There is a growing body of research showing that not only is higher intensity aerobic exercise safe, it may also provide more protective benefits than low-moderate intensity exercise against heart disease when performed by healthy individuals. However, HIIT is not a protocol for those who are brand new to fitness. It has been generally accepted by fitness professionals that a “base” level of cardiovascular fitness should be built prior to introducing an interval program. Persons that are at an elevated risk of cardiovascular disease should seek guidance from a medical professional to ensure interval training is safe for them. I also advise clients to start their workout with a minimum of a five minute warm-up and finish with a five minute cool down during their HIIT workouts.
What are the Fitness Benefits of HIIT?
The greatest benefits of HIIT is a greater increase in overall energy expenditure and metabolism following an exercise session as compared with steady state aerobic exercise. With a steady state aerobic program, the elevated metabolic rate drops back to near resting state nearly immediately following the workout. However, following a HIIT workout, research shows individuals burn an additional 6-15% more calories in the hours following their workout. In addition, research has shown significantly greater gains in cardiovascular fitness for those using HIIT vs. steady state aerobic training.
How Can I Implement HIIT into My Fitness Program?
Assuming you have already built a base level of fitness, start by adding in one HIIT workout per week to your program. It is generally accepted that HIIT workouts tax the body in ways similar to resistance training, meaning your body does need recovery time in between. I generally recommend to my clients that they do HIIT no more than 3-4x/week for a full recovery and best results. Depending on specific fitness goals, optimal frequency of HIIT style training can range from 1-4x/week.
Example HIIT Workout:
5 minute warm-up at a low intensity
5 x 1 minute max effort (>80% Max Heart Rate) / 1 minute recovery (easy relaxed pace)
5 minute cool down at a low intensity
Total Time: 20 minutes
References:
Kravitz, Len PhD, ACSM Information on High Intensity Interval Training, 2014 https://www.acsm.org/docs/brochures/high-intensity-interval-training.pdf
Tabata, I., Nishimura, K., Kouzaki, M., Hirai, Y., Ogita, F., Miyachi, M., & Yamamoto, K. (n.d.). Effects of moderate-intensity endurance and high-intensity intermittent training on anaerobic capacity and VO2max.Medicine & Science in Sports & Exercise, 1327-1330.