Science Behind Les Mills’ GRIT Series / HIIT

Hey, hey!

It’s been cold here. Like bitter cold. I think it’s sort of fun (I’m gonna get hate mail)… a point. I can take it for a few days sure, but like weeks? Wow. I do love the snow though, so I hope it snows some more (just on weekends when I don’t have to drive much. Pretty please?)

I have no idea why I felt I needed to start with a weather update.

Let’s roll with it…..

It’s been quite the opposite elsewhere….It’s actually been hot, hot, HOT in the fitness rooms lately.

(I’m so good at connective sentences)

I love what I do. You’ve heard it a bazillion times, but it never gets old to me. I was born to teach fitness-it’s where I belong, and I am so happy it’s such a huge part of my life!

I blog about what I love, yes, and right now, I am really LOVING coaching GRIT. I just loooovvvve it.


In fact, one of the editors at Self Magazine reviewed Les Mills Grit talked about how crazy tough it was. Cool!

Review of Les Mills’ GRIT Series

She entitled her review “the most intense 30 minutes ever: I tried Les Mills’ New GRIT Series Class”

Hmmmmm. Fitting.

So WHY is that?

Who IS Les Mills International?

I’ll tell you why: Les Mills spend oodles of money on research. First of all LMI (Les Mills International) is a global company that is passionate about stopping the Obesity trend, and stopping it by delivering results in the space of fitness magic.

Les Mills doesn’t just throw some nice moves together in hopes to make money, and if results come, that’s nice. They don’t just switch it up all the time just ‘because.’ NO way. There is research, science, test-classes and sessions, training, coaching, learning, and more that goes on behind each and every Les Mills class, training session, and instructor course.

That’s why I love it. They care, & they prove it time & again that LMI is the top of the fitness class game. It’s not about the money to them, as it most often is in most fitness trends & classes <–in fact, I know from a source that LMI tries their very hardest to keep instructor costs down. Love that.

GRIT is no different than all the other LMI formats–so much research for 1 class. It is a bit different, I guess, in the fact that it’s small group training (so ideally 5-10 people or so), and that the person who leads it is a coach, not an instructor. It’s called ‘small group training,’ so the coach gets IN the face of the participants & coaches them to achieve one last rep, get to one last perfect pushup, or jump 3 inches higher. We as coaches are there to motivate, inspire, and push people’s limits–with them.


Failure equals success in GRIT (and life), after all.

Science Behind Les Mills’ GRIT Series & HIIT in General

So what IS the science behind Les Mills’ GRIT Series exactly? And why is GRIT taking the world by storm so quickly?

It’s the type of training in this series that gets you super fit super fast. That’s why.

GRIT uses the HIIT style (High Intensity Interval Training) to deliver maximum results in minimal amounts of time. In a high intensity interval, you want to work 110% (hence why a coach being right there to motivate you is so key), and then take short recoveries to enable you to do it all again and work 110% once more.

From her review in Self, Amanda says:

My instructor, the adorably-accented Les Mills, Jr. himself, explained that we’d be doing bursts of 110% effort, followed by short periods of rest and recovery–hence the “high-intensity” and “intervals” parts of HIIT.

The brand’s research show that their program works, too: When they had Penn State researchers track two groups of exercisers on professionally-designed workout plans, the group that swapped 60 minutes of cardio for two 30-minute Grit Series sessions lost more than twice as much body fat and saw a four-fold decrease in their triglycerides, one part of total cholesterol. (my edit: more on that here)

What can you expect in a Grit Series class? Non-stop action; even the recovery periods include some type of movement. Lots of squats, jumps, pushups and ups-and-downs from horizontal to vertical–my quads were sore on the stairs for days.

Twice as much body fat lost? Four-fold decrease in triglycerides and one part decrease in total cholesterol? In just 6 weeks? Those are astounding results, especially because the comparison group was already being physically active!

And from Les Mills’ GRIT Series’s page, a bit more explanation:

I love that. I am such a geek when it comes to this stuff, so it’s exciting to see that it’s not just sort of thrown made up ‘just because’. It’s scientifically tested to deliver results faster. These people really got stronger, fitter, and healthier by adding in GRIT to their schedules.

But WHY?

Science delivers results, people.

You can check out helpful videos on this topic on LMI’s GRIT page , but I’ve broken it down for you here:

1. Excess Post-Exercise Oxygen Consumption

-aka EPOC/ calories burned after a workout

-The harder you train, the more calories you continue to burn afterwards. Training at high intensities is a science, and Les Mills’ GRIT takes you there in a way that maximizes the EPOC effect. Ummmm saaahhhweeet.

2. Growth Hormone

-There are chemicals released during HIIT training–when you train hard enough– (an important chemical released: lactic acid).

-Lactic acid stimulates production of Human Growth Hormone, which burns fat and builds muscle.

(perfect combo, eh?)

3. More Fast Twitch Muscle Fiber activation

-More muscle fiber activation equals more muscles working–making the athlete more powerful.

-Most activities (walking, running, etc) use slow twitch fibers, GRIT (and HIIT workouts), use more fast twitch muscle fibers so you unlock more fibers <—creating powerful movements & thus a fitter you

It’s exercise science (and what I got my Master’s degree in), so I love this stuff. It makes ME even more motivated to get people to the gym & trying stuff like this out.

NOTE: contraindications to GRIT (those who shouldn’t do it) include bone or joint diseases, persons not cleared by a doc for intense activity, & pregnancy

Now who wants to fly to SLC & come be a part of my GRIT team?!? 😉


I hope you’re inspired to up your ante in your training–granted of course, you’re cleared to do so. When you train harder & smarter, not necessarily longer, you CAN get fitter. Doing it in a safe, effective environment with great form is key. And of course it’s way more fun & motivating when you have a coach encouraging you to finish each rep stronger than the last…. 😉

Have a GREAT day!! <3

What is a HIIT activity that YOU love to do?? Anyone tried GRIT yet?? How are YOU going to make this info turn into results for YOU??!! <–info is great, but what is powerful is how you use what’s been given to you :)

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  1. Ummm…I just had serious thoughts of flying to SLC to join you for this. It sounds incredible! I’ve always wanted to try a BodyPump class and there’s not much in our area :(

  2. If I was anywhere even remotely close to SLC, I would certainly join you! The class looks so intense, but I can only imagine the kind of results you get from it. I miss Les Mills classes is general, I just go to my school gym right now so they’re not offered.

    I like 10-20 minutes of intervals on the treadmill for my HITT. Short and simple!

  3. Oh man I would LOVE to teach GRIT but the gym I teach at here doesnt have Les mills :( I have to do bodyflow at home, which I actually love doing on my own time! I teach just about everything like you! Spin, bootcamp, toning, circuit training, pilates, core conditioning….Wish I could come take your GRIT class too!

  4. I’m going to make you come back to St. Louis and teach a Grit class so I can try it out myself!!!!!!!! (A girl can dream, can’t she?!)

  5. Is this available to buy on DVD and do at home? I live in a very small, rural area and we don’t have Les Mills classes here :(

    • It is not on DVD right now sadly, (first classes were just launched in November), but it might be eventually! I know the LesMillsPUMP & LesMillsCOMBAT are available as DVDs from BeachBody :) So if you want some LM in your life-at home, that’s where it’s at.

  6. As I’ve told you, I’d love to try out Grit after baby comes! And yes, this weather is a tad bit ridiculous. I think it’s supposed to “warm up” a tiny bit in the coming weeks though. I wouldn’t mind some more snow too, but like you said, only on the weekends when I don’t have to drive in it. 😉 And then the sunshine can come out immediately afterward so it can be blue skies and beautiful white snow. I love those days!

  7. Ah I WISH I could try GRIT, your enthusiasm is what really sells me on it!

  8. Oh man, this looks like a ton of fun!!! So much energy. I wish it would snow hereeee! It hasn’t in like 3 years and I’m not cool with this fact;)

  9. I LOVE your posts like these. Wish I could come and join you at GRIT.

  10. This looks like such a good time and a challenging class. When I am done with my OHC meetings I really do want to come!

  11. Tapping my toes now anxiously awaiting this LesMills class to come out and be available in my gym. Loving the LesMills classes so much!

  12. I would love to fly to SLC and join your Grit team! Haha. However, I was talking to the Grit Captain the other day (we call them captains here not coaches hehe) and she said she’s never gotten so many injuries since teaching it (she teaches BP also)- so be careful :)

    Hm, I wonder what other 1 hr of cardio they compared Grit with? I’d be intrigued to know. As in I think there’d be a fair difference depending on what that cardio was.

    I love Grit, but I can’t do release 2 anymore. Every time I do my knee starts to get buggered and I think it has a lot to do with the squats and getting that bar up and down up and down everytime. Especially with your huge weights- release 3 doesn’t do that anymore- no barbell needed :)

  13. Danielle says:

    okay lady cakes, you’re really making me tempted to try this but i have no time until may, grrrrrr! lol, really though i can’t wait to try one of these classes. sounds fantastic! i’m sold, winner!

  14. Maren says:

    I loved reading this! I told you I was going to come stalk ya. Ha! That last picture above is Nikki in the front huh?! She did our training too! She was a machine and I was in love with her hair! I can’t wait to start coaching this class!

  15. Kimberly J says:

    Where do you teach GRIT in Utah?


  1. […] is teach Zumba (this morn), TJ’s trip (yay!!), date night with my husband, coaching 1 GRIT session, and church. Ahhhhh. Feels so good to have a pretty open slot to do whatever I […]

  2. […] love when new Les Mills’ releases come! Now I need to learn ‘em…. (the GRIT stuff I’ll learn later, once this baby girl is here, since I can’t coach HIIT very well […]

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    Science Behind Les Mills’ GRIT Series | HIIT | Growth Hormone | EPOC | Fast Twitch Muscle Fibers | Enjoy Your Healthy Life



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