06/18/2025
Are HIIT Workouts Good for You?
As a personal trainer, who routinely assigns some form of Cardio Exercise in most training regimens, I’m always asked about HIIT workouts. While I typically lean towards the slow sustained variety, I do understand the need for some clients needing to rev up the engine so to speak. HIIT workouts have many benefits and typically quick results. I’m certainly not opposed to HIIT, but only in moderation with ample recovery.
High Intensity workouts gained popularity because it’s a quick and efficient way to improve your health. But without proper recovery, HIIT workouts can lead to elevated levels of Cortisol into the bloodstream and heightened symptoms of physical stress, even when the exercise isn’t being performed. I've done a lot of research on the topic over the years, to set up my clients for the best outcome possible. Now let’s dive in a little deeper.
What is HIIT?
A HIIT workout consists of short bouts of intense work lasting anywhere from 10 to 60 seconds, followed immediately by a period of active recovery of the same length or longer.
This cycle of hard work and recovery is repeated anywhere from 3 to 10 times, depending on the workout.
Positive physiological benefits from HIIT include elevated post-exercise metabolism, improved body composition, and improved fasting blood glucose and insulin sensitivity.
Performing HIIT workouts, you may see changes within a matter of weeks and walk away feeling a new level of productivity and power. This is why HIIT has been called the “magic pill” of exercise. It only takes a few intervals to experience your body’s heightened level of energy, which is influenced by a fluctuation of hormones, especially cortisol.
What is Cortisol?
Cortisol is one of the many hormones our body produces to handle stress. We all know through television and advertisements that it has something to do with "stubborn belly fat". But it is so much more than that.
During HIIT, the brain senses stress, and a cascade of hormones is released, including cortisol. The release of cortisol activates the sympathetic nervous system, generating a fight-or-flight response. Back in caveman days, this Sympathetic Nervous System response to danger was the key to our early survival, providing our bodies with immediate energy and power to fight or flee when necessary.
Cortisol is responsible for physiological changes, such as the quick breakdown of fats and carbohydrates and a rise in blood sugar for immediate energy and repressing the immune system to focus the bodies’ energy on the potentially life-threatening task at hand.
How does HIIT affect your Cortisol Levels?
Part of what makes HIIT training so effective at turning the body into a lean, fast, and powerful machine is this cortisol response that it generates.
As your exercise is performed at 80%-90% maximum effort, your brain receives the message that your survival depends on this interval, at which point cortisol and other hormones are released, sending you into the Sympathetic Nervous System Response. The body then makes metabolic improvements following this energetically and hormonally demanding experience.
What are some of the Symptoms of Cortisol Overload?
The problem with cortisol is that when our body has too much of it, because of physical or psychological stress, it floats freely in the bloodstream causing negative symptoms to creep into your everyday life. Overtraining Syndrome has some physiological causes, which may include a raised level of cortisol. The symptoms of Overtraining Syndrome include:
Chronic Fatigue
Muscle Fatigue
Decrease in Strength
Mood Changes
Lack of Physical and Psychological Motivation
Sleep Pattern Changes
Anxiety
Consistent Illnesses
Fat Storage
When your body has an imbalance of cortisol, any of these symptoms can be present, even when you haven’t worked out within the last few days.
Ideally, your body should be able to accurately determine when the reaction of fight or flight is most useful and appropriate. But too much HIIT can confuse the brain into signaling a protective response even when our bodies are supposed to be calm or at rest.
Everyday tasks might leave you feeling agitated because your body is misinterpreting everyday stress as life threatening stress.
Because HIIT solicits such a powerful reaction from our sympathetic nervous system, it’s critical to prioritize recovery when your workouts are frequently of high intensity.
What is the Importance of Recovery?
In contrast, the Parasympathetic Nervous System is responsible for sending the body into rest, digest, and recovery mode. Recovery between intervals and recovery days between workouts are key to seeing positive physical results from your HIIT workouts. The quality of your recovery is also important, and can be enhanced with different practices, including:
Sleep
Good Nutrition and Hydration
Foam Rolling or Massage
Abstaining from Intense Exercise
Most importantly, this kind of workout should be performed 2–3 days a week at most, with rest days between each HIIT session. If your body is constantly in a state of stress, the positive effects of HIIT can be reversed, with your hard work working against you. Only through proper recovery and rest will you see the true benefits of your efforts. Mike Pieper PhysiqueWorx Fitness
