When To HIIT It & When To Quit It
Learn how to do high-intensity interval training (HIIT) the right way for better body composition, metabolic health, and sustainable weight loss.
Interval training doesn’t have to be high intensity! In fact, Hitting max-effort intensities on a daily basis is not sustainable for long-term health, body composition, and hormone balance.
I was a HIIT bunny for many years and used this style of training exclusively nearly every day. It was an approach that delivered great results at first, but quickly dropped me into an all or nothing burnout cycle where I couldn’t stay consistent with exercise.
Now, as someone who has broken up and made amends with high-intensity interval training (HIIT), my goal for this blog is to help you implement this modality more effectively—and maybe even look forward to it!
A Misused Modality
Training at high intensities can bring a wealth of physical, mental, and emotional benefits. It’s a great way to challenge your stamina and provides an outlet for emotional stress. It can help you flip the fat burning switch as part of your weight loss strategy or be a fun way to test your limits.
However, as with any practice that promises positive outcomes, the trouble with HIIT is that so many of us mistakenly believe that more is better. Which just isn’t true for max-effort workouts.
As a modality, HIIT is not designed for everyday use. In fact, a 2021 study suggests that chronic max-effort workouts can, “compromise mitochondrial function and blood sugar regulation and may increase the stress hormone cortisol.”
To add insult to injury, increased cortisol and insulin resistance are already common in the luteal phase for menstruating women which can compound the detrimental effects of overdoing HIIT workouts.
Fighting Female Physiology
Our female survival strategy, though intelligently designed, is largely to blame for the diminishing returns of repeated HIIT workouts. This is because the human body interprets excessive exercise (like daily HIIT sessions) as a threat wherein the energy demand greatly exceeds our energy supply.
When this happens for men, their survival strategy prioritizes performance by maintaining muscle and burning fat. Conversely, when this happens for women, our bodies ditch metabolically expensive muscle tissue and preserve energetically stable fat as a form of efficiency and preservation.
In practical terms, this means that yes, you may burn an outrageous number of calories during HIIT sessions and continue operating at a higher metabolic rate for some time afterward, but this is only a stop gap to meet your body’s short-term energy needs.
In the long run, your body will cleverly adapt by storing more fat as a reliable long-term solution to meet the repeated high energy demand.
The result? Many women who use HIIT workouts for weight loss actually end up storing fat and wasting muscle.
When To HIIT It
This doesn’t mean that you have to break up with HIIT for good. So let’s talk about when to HIIT it and when to quit it.
You may have heard that the follicular phase is the best time for high-intensity interval training (HIIT). From a physiological standpoint, this holds true because:
We have better stress resilience with less sympathetic drive (stress) from hormones & our bodies recover better.
Metabolism slows with a lower baseline demand for essential functions. This leaves more energy reserves for exercise.
Our bodies utilize carbohydrates well which provides quick energy during exercise & makes high intensities feel more accessible.
When performed as intended however, HIIT is not suitable for daily practice—even in your follicular phase!
This is because HIIT demands a max-effort output where you are pushing up against your intensity threshold. Your HIIT workouts will therefore require a significant rest and recovery period (> 24 hrs) afterward.
Hitting max-effort intensities on a daily basis is not sustainable for long-term health, body composition, and hormone balance.
Don’t get me wrong, I love HIIT workouts, but I love them even more when they are used in a cycle-informed way that allows me to enjoy the benefits (improved conditioning, healthy metabolism, fat burning, etc.) without dipping my energy account into the red.
Here are a few recommendations for implementing HIIT for better results:
Sustained max effort during every work interval
Vary recovery intervals as needed for full recovery in between
1-2 sessions/week max in the follicular/ovulatory phases
20-30 minutes or less with an appropriate warm-up/cool-down
2-3 days dedicated recovery time and fuel in between
Avoid HIIT workouts in a fasted state
When To Quit It
Now that you know how/when to hit it, let’s touch on when to quit it. In general, it’s best to avoid HIIT altogether in your luteal phase. This doesn’t mean your workouts have to be easy, but they shouldn’t max you out. Here’s why:
Stress resilience decreases in the high-hormone luteal phase
Faster metabolism trends toward catabolic which can break down muscle
Cooling is less efficient & stamina decreases
Fat is the preferred fuel source during exercise (not ideal for hitting high intensities)
Let go of the guilt around skipping the high-intensity sessions during your luteal phase. You’re actually doing your physiology a favor!
Finding Your Edge
Unless you’re well versed in sprint training, it can be challenging to find your edge or understand what a “max-effort” output truly feels like.
As discussed in above, there are many benefits to high-intensity interval training (HIIT)...when it’s done right.
However, a common mistake that many women make (I’m guilty too!) is attempting repeated max-effort outputs w/o full recovery e.g. a series of high-intensity movements performed using 40/20 intervals. If you don’t have a chance to recover before the next max-effort interval begins, the stress signals compound & cortisol floods your system.
This can result in unfavorable metabolic states where you store fat & shed muscle to preserve energy, especially in the luteal phase.
Still, you’ll find that most interval workouts include a prescribed rest interval that doesn’t always allow full recovery. This is not inherently bad, but it means that your output will likely diminish i.e. you won’t hit the same intensity every interval.
So, while this framework is often used for “HIIT” workouts, it is better suited to circuit training or other modalities where your output/recovery aren’t meant to max out every time. In other words…
Interval training isn’t always high intensity.
HIIT In Practice
To perform at a truly high intensity, it’s important to know what your max-effort output feels like—lungs burning, lactic acid building, flirting with discomfort. And you can only create this level of output from a recovered state.
The key to HIIT is working less & resting more. If you’re giving 100% in each interval, your session will only be 10-15 min long (+ you’ll be happy about it!) Or, you’ll give yourself enough time to fully recover in between bursts of max effort.
To help you find your edge, try the two sprint interval workouts below and remember to go all-out! Trust that complete recovery will be ready for you after every push.
Be Strategic
Remember, high-intensity interval training (HIIT) can be an incredibly effective tool for boosting fitness, conditioning, and fat loss, but it’s important to be strategic.
HIIT is not meant to be an everyday practice, especially for women who experience natural fluctuations in energy and stress resilience throughout their menstrual cycle.
Learning how (and when) to push your limits and prioritize recovery (by aligning your training with your cycle) can help you maximize the benefits of HIIT without compromising long-term health, hormone balance, or body composition.
Ultimately, knowing when to HIIT it and when to quit it will help you find a sustainable path toward achieving your fitness goals while respecting your body’s unique needs.
