The Great Cardio Debate – Part 2: The Case for Interval Training

Welcome back! If you haven’t read The Great Cardio Debate – Part 1: Is Cardio Really King?? check that out, too!

It hasn’t always been this way but when most people think of cardio now, they immediately think of interval training, also known as metabolic conditioning or high intensity interval training (HIIT). Interval training is a term used to describe workouts that involve periods of (often very challenging) work followed by (often very brief) rest and recovery periods. It’s something most people either love or hate. For people who love a challenge, it’s insanely awesome but people on the other side of the love-hate fence have used words like “jarring” and “abusive” to describe it.

Love it or hate it though, most people find it far less boring than trudging along on the treadmill, sidewalks, elliptical, rower, bike, or other commonly-used steady sate cardio method for what feels like hours on end. And I gotta tell you, you’ll feel pretty awesome when you complete a HIIT workout- like you can take on the world and who doesn’t need more of that feeling in their lives??

Interval training, specifically HIIT, has been used in coaching athletes for a long time because it’s incredibly efficient but it wasn’t until the past couple of decades when those outside of sports became aware of its benefits and started to add it to their own routines…now it’s EVERYWHERE. It’s the premise behind almost every super-popular, heavily-marketed, trendy workout out there right now, ranging from the more basic and fun forms through the more extreme (and sometimes a little scary) forms.

So, let’s talk about the upsides (and there are many):

  • It’s extremely time-efficient because the workouts are much shorter than your average walk or run in the treadmill
  • Burns more calories than steady-state cardio over the same workout duration
  • Places a greater demand on your body to recover from the effort causing you to burn more calories after the sweat session is over when compared to steady state cardio- this is known as “afterburn”
  • Burns more fat (possibly due to afterburn), some studies even showing that it’s up to nine times more effective at fat loss than steady state training
  • Improvements in aerobic capacity have been found to occur 3-4 times faster through HIIT than steady state cardio
  • It’s mostly anaerobic, meaning that during exercise, your body is fueled primarily by stored carbohydrates rather than relying exclusively on oxygen
  • Trains your body to transition easily between burning fat and burning carbs more efficiently which has tremendous benefits in both sport and in life

But HIIT is not the magic pill folks. Although it’s hot right now and there’s little discussion of any limitations or concerns related to HIIT, as with most things, too much of a good thing can be awful. If it’s the only form of cardio that you do, there are some downsides as well, particularly when done regularly over several months:

  • Anaerobic fitness is awesome but there is only marginal benefit to your overall aerobic fitness so you’re missing a huge chunk of the cardio benefits by not training your heart and muscles in the heart rate zones that are closer to the aerobic zones where you spend the vast majority of your daily life
  • Can give you the false impression that you’re super fit because, despite being anaerobically fit, a complete lack of steady state cardio can result in a higher resting heart rate- an indicator of aerobic weakness
  • Rapid improvement leads people to want to do more HIIT more frequently but more is not necessarily better
  • Long-term HIIT can be mentally and physically brutal- some studies even showing that after only a month or two of using HIIT as your only form of cardio, the benefits are reduced and the strain on your system may actually be doing more harm than good
  • It can have negative effects on your nervous system triggering symptoms that closely-resemble anxiety, like an elevated heart rate, sleep disturbances, higher body temperature, excessive sweating when not working out, lack of attention, inability to focus, agitation and restlessness
  • It’s not meant to be done every day particularly over long periods of time and when it’s used this way it can lead to aches and pains, fitness plateaus, workout burnout, and in some cases injury can result

That’s a lot of information, right?? And that’s the simplified version (you’re welcome). So what have we learned? If used wisely, interval training is an extremely powerful tool that will help you reach your fitness goals quickly and safely; however, you should know that it’s not going to fix all that ails you. So while it’s an excellent tool to have in your toolbox and tends to make you feel like a superhero, interval training (like every other form of exercise) should NOT be your only workout. Yep, even if you LOVE it, sorry.

Time to move on to what I believe is interval training’s undervalued big brother- steady state cardio. I don’t say this because I’m a long-distance runner either. I love a challenging HIIT workout as much (if not more than) the next guy but by ignoring the benefits of steady state cardio, I believe we’re doing ourselves a big disservice by missing some key cardio benefits and leaving ourselves with the impression that our cardiovascular systems are in better overall condition than they actually are. In my next post, we’ll explore the less glamorous but equally important steady state cardio.

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