HIIT (High-Intensity Interval Training) is an interval training approach that involves repeated bouts of high-intensity exercise, mainly aimed at increasing metabolism and maximizing oxygen uptake. During these periods, your heart rate rises to 70–100% of its maximum capacity. Alongside these high-intensity intervals, low-intensity recovery periods are also performed.
Another important component of HIIT is rest between cycles in order to restore energy, which is essential for completing the training session.
Main components of HIIT
Intensity
The key feature of HIIT is its high intensity in each training round. The intensity should be challenging and push you to use your maximum capacity.
A HIIT session usually lasts between 20 to 30 minutes.
Work intervals are typically short, ranging from 20 seconds to 2 minutes.
Rest periods are also short, allowing partial recovery before the next intense interval, usually lasting from 10 seconds to 2 minutes.
Benefits of HIIT
- Increased post-exercise oxygen consumption (EPOC) and therefore increased metabolism, leading to higher calorie burn
- Help for people with lung conditions
- Lower blood pressure
- Improved cardiovascular health: HIIT has been shown to improve VO2 max (the maximum amount of oxygen a person can use during intense exercise)
- Increased insulin sensitivity, helping muscles use glucose more efficiently for energy
- Improved cholesterol levels
- May reduce blood sugar levels and help people at risk of type 2 diabetes (Source 1, Source 2)
The other side of HIIT
While HIIT has many benefits, if it is not paired with proper recovery, it can increase cortisol levels in the bloodstream and worsen physical stress symptoms.
Cortisol is a hormone produced by the body to manage stress. During HIIT, the body releases cortisol because the brain perceives stress. This activates the sympathetic nervous system. (Source)
Cortisol regulates the body’s stress response and controls how the body uses fats, proteins, and carbohydrates.
When cortisol levels remain too high, it can lead to negative effects over time.
Overtraining syndrome may also increase cortisol levels. (Source)
Possible symptoms include:
- Anxiety
- Lack of physical and mental motivation
- Chronic fatigue
- Reduced performance during workouts
- Changes in sleep patterns
- Insomnia
HIIT should ideally be performed 2–3 times per week and combined with proper recovery, including rest, nutrition, hydration, and mental and physical relaxation.
Who is HIIT suitable for?
HIIT should be adjusted to each individual’s condition. In general, people with severe overweight, older adults, or those with medical conditions should consult a doctor or trainer before starting this type of training.
How HIIT is performed
There is no standard HIIT workout. Since it focuses on heart rate and intensity, it can include any type of exercise such as running, cycling, swimming, weight training, or bodyweight exercises.
Tabata method
Tabata is one of the most popular forms of HIIT. It lasts only 4 minutes: 20 seconds of high-intensity work followed by 10 seconds of rest, repeated 8 times. It may sound short, but when done correctly, it feels extremely intense.
Summary
HIIT is hard, but it has a powerful impact on both physical and mental health. If you have medical conditions or are just starting out, consult a professional before doing it.