Welcome to high intensity interval training. 

Seven years ago, I would have classified myself as physically fit.  On a weekly basis, I started most mornings with a leisurely run, instructed three BODYPUMP and two BODYFLOW classes, and completed another couple of group cardio formats.  I was exceeding the activity guidelines because I was lucky enough to have a flexible schedule that allowed me to do the things I love: exercise outside with my dogs and exercise inside with my friends.  So, when Bryce Hastings asked me to test a new high intensity interval training class created by Les Mills, as a scientist I was excited to study it and as a fitness enthusiast I was excited to do it!

Fast forward through months of protocol development and human research approval: Sheldon McBee, a master trainer for Les Mills, traveled to State College to teach the first group of instructors (Claire Colebrook, Rachel Rajkowski, Boris Rebolledo, and me) how to coach this novel session.  Our preparation, of course, included Sheldon leading us through an actual workout…

During which the following thoughts went through my head.

What is this?!?!

When is this going to end?

Are my lungs going to explode?

Are my legs going to fall off?

Is anyone else feeling like they are going to die?

Am I going to die?

Please can I just die now?!?!

Welcome to high intensity interval training.  This is what exercising above 90% heart rate max feels like to me.  And after seven years of two high intensity sessions per week, it still feels like this to me!  It does not get easier.  But I have never felt more fit.  And this is not anecdotal: the research on the Les Mills GRIT series and Les Mills SPRINT is compelling.

For the original HIIT study, we collected data on 84 healthy adults who were currently meeting the weekly physical fitness guidelines of 3 cardio and 2 strength workouts.  Half the participants replaced one of their cardio sessions with two high intensity sessions each week for six weeks. 

Mean body fat, fasting blood glucose, and triglyceride concentration all significantly decreased while strength and cardiovascular fitness increased in the group that completed the high intensity protocol.  This is incredibly impressive considering the participants were already physically fit!

Numerous reviews with a focus on HIIT have demonstrated similar superior outcomes for body composition, metabolic disease risk and cardiorespiratory fitness in various clinical populations.  In short, REAL, above 90% heart rate max, lungs exploding, legs falling off, feeling like death training can change your fitness level in a short period of time.

This is why I am critical of casually using the term HIIT.  It is false advertising to promote a format with extreme benefits if you are not delivering the extreme intensity.  And let me repeat: exercising at this maximal intensity is not necessary to be healthy and fit.  If you honestly dread the thought of a 30-minute workout with intervals at this level, forget about it!   Finding a cardio routine that you enjoy will provide all the physiological benefits through consistency.

Next week:  can there be too much of a good thing?

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8 Responses

  1. Looking forward to reading next weeks topic too! I think the answer is Yes, as I found out the hard way not long ago 😉

    • EXCELLENT question! The only time I would not recommend is soon after you wake up in the morning… especially for high impact HIIT. There is a greater risk of back injury without allowing the spine to adapt to being upright and mobile. So anytime that you feel excited and ready to push yourself after at least 2 hours from getting out of bed.

  2. Thank you Jinger and as a participant in both the GRIT and SPRINT studies I know HIIT really works. When I told my Medical Doctor about SPRINT he said “Keep doing SPRINT”. If anyone says SPRINT is easy then they are not using enough load. Look forward to future post from you!!!

    • You are SO right! Les Mills GRIT CARDIO and SPRINT can be as cruisey or challenging as you want because it is the responsibility of the participant to move faster (GRIT CARDIO) or add more resistance (SPRINT). The intervals are designed so that you have enough recovery to dominate the next work effort but not let your heart rate drop back into the moderate zone. Miss you in SPRINT!!!

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