3 HIIT cardio mistakes I made in my early 20s

Last week I talked about how keeping an open mind and putting trust in the process can help you to break out of a fitness rut, and I promised a follow-up post about the 3 HIIT cardio mistakes I made in my early 20s. It’s time for that sequel!

Before getting started, I want to preface this by saying that I’m not anti-cardio, even though it might come off this way because I do far less now than I used to. Everyone has their own reasons for doing cardio, and for many of us, it’s the mental release. Going on a long run has always been one of my favorite ways to clear my head, solve problems that have been weighing on my mind, and mentally plan out my day ahead.

Another motive might be performance-related. If you’ve signed up for a competition that requires cardiovascular endurance, it’s pretty obvious that training should include that type of activity. But I think one of the biggest reasons a lot of people do cardio (and I will flat out admit this was a big driver for me in my early 20s) is because of a desire to lose body fat.

As much as I’m 1000% all about self-acceptance and beauty at any size movement, I don’t think there’s anything wrong with having physique-related goals. Having lost 70lbs in my late teens I can very much vouch for the value in the lessons learned, the confidence boost I experienced, and the discipline I developed that has carried over into other aspects of my life. My goals now are more focused on developing strength while maintaining mobility, and I know these will be even more important as I get older. However, I also realize that plenty of you reading might currently be working towards fat loss/body composition-related goals. My hope is that sharing the mistakes I made will allow you to learn from me and achieve your own goals faster.

First things first: what is high intensity interval training (HIIT)?

As an acronym that quickly made its way into pretty much every health + fitness magazine a couple of years ago and continues to be something experts rave about, it’s gotta be pretty wonderful, right? Google will turn up a bajillion slightly different definitions, but there are 2 common things to highlight:

First: HIIT is a training method that involves alternating between short periods of very high intensity efforts (work intervals) and low intensity efforts (rest/recovery intervals).

Pretty straightforward, right? Ok, try and stick with me for this next one.

Second: Our bodies tap into our anaerobic metabolic system instead of the aerobic energy system for HIIT because this allows for faster access to energy needed to perform high-intensity movement.

With the anaerobic system, the body gets energy super quickly from adenosine triphosphate (ATP) and other chemicals in our bodies. The tradeoff though, is the length of time that energy source lasts.

After a minute or two (depending on how well-conditioned you are), the anaerobic system becomes tapped out and we make the switch over to the aerobic system. (Anaerobic = without oxygen, aerobic = with oxygen.) The body uses oxygen to break carbohydrates and fat into energy, but this takes a little longer to happen. When the aerobic system is being used, we just can’t maintain super high intensities. As a result, we’re forced to slow down.

To apply this to types of workouts, think of the anaerobic system as the one you’d use for a HIIT session, and the aerobic system as the one you’d use for anything from a 5k race, a 1-hour spin class, or an ultra marathon.

Still with me? Ok. Let’s talk about where I went wrong.

The 3 HIIT cardio mistakes I made (+ learnings, so you don’t have to do the same!)

Mistake 1 (the biggest one): Spending to much time in ‘the mushy middle’, and making my “high intensity” intervals too long.

Despite knowing those facts above about how HIIT is supposed to be done, the endurance runner/cardio junkie in me used to spend a lot of time logging junk miles – as in, ones that weren’t hard enough to force my body to change, and not easy enough to allow for proper recovery. I was so hell-bent on numbers – speeds and interval lengths – and not paying enough attention to how my body really felt.

For additional context, my usual training runs lasted an hour at minimum. Being used to that, my stubborn mind decided that anything less than 30 minutes was too short to truly be considered a proper session. And so, I’d do what I called “HIIT sessions” for 30+ minutes with some hard efforts and kinda-moderate-but-certainly-not-recovery-pace breaks. As you probably guessed, instead of a nice steep up-and-down heart rate curve that you’d see in someone doing HIIT properly, mine was more like a shallow wavy line. Like a weak handshake, a damp cloth and a lukewarm shower. The definition of “meh” when it comes to HIIT, and precisely what not to do if the goal is to burn body fat.

Before we move on from this reason, I need to tell you more about why it wasn’t effective. You might be thinking “but surely you burned more calories this way, and more calories burned means more weight loss, doesn’t it?”

That’s kind of the case (and the fitness industry has certainly taught us to think it’s the truth), but there’s more to it. To sustain those 30+ minute sessions I was inaccurately calling HIIT, my body had to be using its aerobic energy system. With carbs and fat as fuel and oxygen as the ingredient needed to turn them into energy, I was training myself to become more efficient at that level of intensity. Had I been doing HIIT correctly, the high-intensity bursts would have been far more disruptive to my body’s status quo, would have created greater demand from all muscles and systems involved, and would have been more effective in stimulating fat loss.

How does this tie back to that calorie burn?

As a distance runner whose aerobic system was very efficient, I was able to endure long distances and training durations. When training for my half Ironman, my watch would report 4-digit calorie burn numbers at the end of my longest sessions. While endurance was required, strength really wasn’t. Case in point: my super flat butt, and multiple physios diagnosing my injuries as a result of “weak glutes”. I know I’m not the only runner who has heard this!

Now compare long distance running to sprinting on a track, sprinting up a hill, or swinging a kettlebell. These things all signal a need for explosive power and strength, but there’s no way you could do any of them with good form for 30+ minutes, and even at max effort for whatever time you can muster, you wouldn’t rack up the calorie burn that you would in, say, a 10K run.

So how then, can HIIT be better for fat loss if the calorie burn in a HIIT workout isn’t as high?

The explosive, powerful movements in HIIT require strength. Strength requires muscle. Muscle requires more calories to exist on our bodies than fat, so a person whose body has a higher percentage of muscle relative to fat is going to have a faster resting metabolism. In other words, they burn more calories at rest than their less-muscle-y friends. You might burn 4x the number of calories on the treadmill as someone doing a HIIT session for a much shorter time, but that person (assuming they have a higher ratio of muscle to body fat) is going to be burning more calories later throughout the day – even if they’re just sitting on the couch.

Ok, take a break. I promise, the next 2 mistakes are much shorter and easier to explain now that you’ve wrapped your head around mistake #1.

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Mistake 2: Trying to do HIIT sessions too often.

HIIT can be done in all sorts of ways – running, with bodyweight, dumbbells, kettlebells – really anything that requires powerful movement and sends your heart rate skyrocketing. In a sense, the high intensity is kind of like sending your body into a state of emergency, as if you were trying to outrun a hungry bear or escape a life-threatening situation. Your body goes into WTF mode, and just like any big stressor, that impacts your hormones and nervous system. You know how occasional stress is good for us and teaches us to be resilient, but chronic stress is no bueno and can lead to inflammation and disease? The same applies here – more is not better, no matter how amped you are about crushing fat loss goals.

There was a time when I tried to do a HIIT session at the end of every workout, and while the endorphins always felt lovely at the end, the consequences certainly caught up with me. I began to notice feeling more fatigued before I started my workouts, wasn’t recovering as quick as I had been previously, and (you might have already guessed it) got injured.

This brings me to the 3rd and final mistake….

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Mistake 3: Not focusing enough on mobility.

We’ve established that HIIT, regardless of whether or not you actually do it with weights, is like strength training. You need strength to move explosively, and two crucial pieces to the puzzle of building strength (and muscle) are recovery and proper mechanics.

When we add speed to anything explosive (like a sprint), we put ourselves at risk of injury. When movement patterns are already not ideal because our muscles are already too fatigued (see Mistake 2!), and due to things like imbalances (which I definitely had back then), the risk becomes greater. A lot of my imbalances were/are due to overcompensation from some muscles in order to make up for weaknesses in others. In my cardio junkie days, I was extremely quad dominant, had weak glutes, mega tight hips, and over-pronated with every foot strike. If I could go back in time, I’d put WAY more emphasis on mobility work in order to loosen up the areas that were leading me to injure just about everything down the lower left side of my body, from my SI joint to my Achilles. That, and I’d smack myself for every time I decided 1 more junk mile was a better idea than foam rolling. That’s a lot of smacks.

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Oh. Emm. Geeee. We made it. Let’s finish up with this:

Despite knowing what proper HIIT was supposed to look like, for some reason it took me years to finally trust the process and do it properly. Not surprisingly, when I let go of my stubbornness and gave it a solid try, that’s when the results appeared. (Who’d have thought?!) The good news for you is that it doesn’t have to take years to achieve the same – you’ve got the learnings right here! If you’ve been trying to use HIIT as a tool for fat loss but don’t seem to be making much progress, I’d really encourage you to take an honest look at how you’re incorporating it into your fitness routine. If you’re making the same mistakes that I did, try to let go of any preconceived ideas and attachments to specific numbers – reps, paces, work intervals, rest intervals, etc. Instead, tune into your body’s cues, make the work intense, make the rest real (even if it feels like you’re moving backwards), keep that form on point, and don’t forget to stay limber!

Tell me… what have your experiences with HIIT been? Positive or negative, I’d love to hear them, as well as any questions you have left after reading this marathon-length blog post!