Why Your HIIT Training Isn't Hiiting The Spot

Have you been living under a rock for the past few years? Everyone knows about HIIT training. It’s the secret to quick weight loss - no pun intended. Companies like Crossfit have monopolized on the concept of High Intensity Interval Training to help thousands of people reach their health goals. That being said, the secret to HIIT training is working at a high intensity. In fact, the words high intensity don’t capitalize on the truth. It should be called maximal intensity. That’s why the concept of doing something like Crossfit is so intimidating. It’s a maximal effort workout, which means it takes maximal effort. I ‘aint got no time for that.

Well, actually you do. You’ll have even more time than if you hopped on a treadmill and muscled out a 3 mile jog. The idea of giving a maximal effort is romantic at first, but during the actual workout you’d rather be divorced from the very concept. A maximal effort literally means that one more step, one more breath, one more heart beat is more than you can physically do. You’re maxed out. Once you’ve maxed yourself out you collapse, catch your breath, and then hop back up to do it again. That’s the interval part. HIIT training only works when you give everything you have and then collapse and do it again a couple of minutes later. But how exactly does a few seconds of work translate into faster weight loss?

HIIT training is a very expensive process. When someone runs countless miles on end they increase their RER (respiratory exchange ratio) during the workout. Oxygen is required to burn fat, and each liter of oxygen you consume burns 5 calories. So when someone runs they increase their RER which increases the need for Oxygen which increases the amount of fat used for energy. That’s why running is a popular tool for weight loss; at the surface level it looks like the best way to burn fat. However, once that person stops their run the RER returns to normal in just a short period. However, when the very expensive HIIT training is used several debts are made. There is an oxygen debt because a true HIIT workout will have sets that last less than 2 minutes which makes then anaerobic (without oxygen). This also depletes blood sugar because that’s what the body uses for fuel instead of fat and oxygen. The result of maximal anaerobic work and blood sugar depletion is a metabolic debt which causes the person’s RER to be elevated for up to 48 hours.

So instead of having an elevated RER for an hour someone who does HIIT has elevated RER for 2 WHOLE DAYS (causing more fat burning for longer). I don’t know about you, but that’s my kind of fat burning. Sit on the couch and burn fat because I did some max effort sprints yesterday. Win Win.

Here’s the problem though. A lot of people take the idea of HIIT training to their gym and training partners. Everyone loves it. They all clink their shaker bottles together and have a good laugh at all of the fat that they’ll lose. After a round of high fiving and chest bumping (bro version) they start their workout. It’s not HIIT training though. What happens is that they wind up doing sub maximal work for a few rounds, get sweaty and out of breath, and then wait for the RER benefits. But they never come.
This isn't HIIT, this is a circuit. 50 second planks are not maximal intensity
People can’t follow half of the science for all of the results. It’s all or nothing.  In most cases it’s probably nothing. When you leave a HIIT workout you shouldn’t be thinking that you could do some more. You should actually consider never working out again and that all of existence is vanity.

So if your HIIT training isn’t working then you might want to actually do HIIT training. Just a thought. 

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About Me

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BS, MS - exercise Physiology
EPC - Board Certified Exercise Physiologist

Published Thesis
The impact of three different forms of warm up on performance

The Effects of Glucose Supplementation on Barbell Velocity and Fatiguability in Weightlifting - A pilot study"

The Accute Effects Of Different Squat Intensities on Vertical Jump Performances
The Accute Effects of Different Squat Intensities On Jump Performance

Graduate from Midwestern State University, founder of Endunamoo Barbell Club, and Endunamoo Strength and Conditioning. Working to help athletes physically reach their goals and achieve scholarships while spiritually pouring into as many people as possible on all platforms.