High-Intensity Interval Training (HIIT) - The Apeiron Life Perspective
- Elizabeth Bradley, MS
- Aug 17, 2022
- 5 min read
What it is:
High-Intensity Interval Training (HIIT) is an exercise training method where short bouts of maximal or near-maximal efforts (80-95% max heart rate) are followed by relatively short recovery periods. The duration, intensity, and frequency of the interval training session can all influence adaptations. Reviewing data from your Heart Rate Monitor can help you understand the physiological response to the interval training session and, over time, may give insights into fitness and fatigue. Some researchers have suggested that Interval training should be referenced as high-intensity interval training (HIIT; ‘near maximal’ efforts) or sprint interval training (SIT; ‘supramaximal’ efforts). Both HIIT and SIT interval training have been shown to promote physiological adaptations similar to those observed following moderate-intensity continuous training (MICT) (e.g., increased aerobic capacity (VO2max) and improved mitochondrial content).
A variety of interval training programs have been shown to produce similar cardiovascular and peripheral mitochondrial adaptations. Popular interval training programs include interval durations that range from 15 secs to 4 minutes. The work relief ratio (amount of recovery expressed as a ratio to the work time, e.g., 60s on 60s off = 1:1 W:R) is one of the most important factors in designing an efficient HIIT or SIT program because the recovery interval helps support the exercise intensity. Also important is the overall training volume, which is influenced by the number of intervals and the weekly interval training frequency. Improvements in VO2max by more than 5% have been observed following 6-8wks of interval training using 12x30s, 10x60s, and 4x4min formats. Training intensely can be performed during running, cycling, swimming, body weight, aqua sports, group classes, and many other great forms of movement.
When designing a HIIT workout, some factors to consider are fitness level, type of exercise, and workout length.
Fitness level - People who are new to exercise should start with shorter work intervals and longer rest intervals (e.g., 20 secs work followed by 40 secs of rest or a 1:2 ratio). Once your fitness level improves, you can move up to a 1:1 ratio and even a 2:1 ratio.
Type of exercise - The more challenging or demanding the activity, the more rest you need. Tuck jumps and burpees will spike your heart rate and demand more from your nervous system as well as your tendons and ligaments than lunges and squats.
Workout Length - Generally, HIIT workouts don’t go beyond 30 mins. When working on all cylinders, you can’t keep the intensity up much longer. In general, you know when you’ve hit the sweet spot when you feel you’ve done a great, challenging workout but you’re not entirely wiped out for the rest of the day.
The types of HIIT are broken down by their ratio of exercise to rest.
Standard HIIT 1:1 - Repeated reps of high-intensity work followed by a rest period of equal measure.
For example, a sprint of 45 seconds followed by a rest period of 45 seconds.
As you improve, you can decrease your training sessions to a 2:1 ratio— for example, a sprint of 1 minute followed by a rest period of 30 seconds.
Lactic Acid Training - Rest time decreases as your lactic acid tolerance increases. Begin training at 1:4, then as you improve, increase to 1:3, and finally a 1:2 balance of work to rest training sessions.
For example, a sprint of 1 minute followed by a rest period of 2 minutes.
The Original Tabata 2:1 (Izymo Tabata's workout) - 20secs/10secs work-rest ratio for 8 intervals, lasting a total work time of 4 minutes. Overall it involves short bursts (~170% of VO2 Max) before an extended rest of the equivalent time takes place.
Cardio is not the only type of interval as you can incorporate movements such as utilizing body weight or lifting weights.
For example, you can perform circuit training with weighted squats, burpees, and press-ups using the same ratio of timed sprints and rest periods.
Reasons for performing HIIT: It effectively improves aerobic fitness, assists weight loss, and improves other health indicators. The compressed time a HIIT workout takes can produce comparable results to longer or moderate intensity exercise; therefore, appropriately utilizing HIIT can increase the potential to reach your goals and objectives quicker.
Purported claims:
Increases overall oxygen uptake, and VO2 max
Higher overall calorie burn during, and continuation after exercise
Accelerates body composition restructuring (Fat loss, muscle gain)
Increases muscle energy generation
Improves fat oxidation and utilization
Minimizes training time whilst maintaining endurance, speed, and strength goals
Improves lactate uptake, and clearance
Improves longevity and cell turnover
What the science says:
Exercise in all forms is beneficial, but HIIT has many well-built studies showing a whole host of advantages.
Longevity and Cell Rejuvenation. One study showed bounding improvements across a group of adults aged 18-80 years in their mitochondrial function and energy-producing capabilities.
Metabolic Function and Illness Prevention. Improvements in body composition ratio, excess fat reduction, lean muscle mass gain, and improved insulin sensitivity. A 2022 study recently showed how HIIT boosts the number of proteins in skeletal muscle to prevent and treat metabolic diseases through energy metabolism.
Cardiovascular Disease Risk Reduction. One study determined a program involving HIIT three times a week for just twelve weeks improved vascular function.
Improved Brain and Mental Capabilities. Recorded improvements in combatting cognitive decline and increased mental health well-being.
Studies have shown just 3 30-minute HIIT sessions per week involving warm-up, cool-down, rest intervals, and ≤10 min of intense exercise can improve aerobic capacity, skeletal muscle oxidative capacity, exercise tolerance, and markers of disease risk after only a few weeks.
Continued oxygen consumption (EPOC) and energy expenditure (EE) have been shown to be higher in HIIT workouts. This is because both calorie burning and oxygen utilization continue after a HIIT session is complete.
Our take:
HIIT is an excellent method to incorporate your favorite activity more efficiently. It may also improve your likelihood of participation in a training routine as it takes less time away from your family and friends.
One of the main factors of HIIT is the way it stresses the body and how the body recovers and adapts to bear a greater load next time. HIIT might be even more important for older adults due to its ability to elicit favorable adaptations in the skeletal muscle by increasing mitochondrial content, which can stave off age-related muscle weakness.
However, recovery is vital. Knowing when to rest as the body is exhausted is just as important as consistent training sessions. Adequate recovery time will allow you to reap the full benefits of HIIT without overtraining.
Will this benefit you?
High-intensity training can place a more significant strain on the body and system. Therefore a gradual introduction and increase in exercise intensity is needed to avoid injury and immune system overload.
A few studies have shown varying results in the time needed to see benefits. One such study showed an aerobic capacity increase during a 1:1 ratio of 60 seconds but not in intervals of 30 seconds. The need for more understanding does not negate the known advantages. It just means working closely with professionals who have a greater knowledge of what works best for you.
Still curious to try it? If you do, here’s what to keep an eye on:
Start with a higher rest vs work ratio and gradually decrease as your training improves to prevent the risk of injury or cardiovascular issues.
Begin with one weekly HIIT training and extended recovery time alongside your usual workouts. Increase as you feel ready.
Leave 48 hours between HIIT sessions for recovery but do participate in other moderate activities and training practices.
If you decide to perform any tests, such as a Wingate test, make sure it is under the supervision of your personal trainer.
References and additional reading:
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