By Dr. Ayla Donlin, Special AFS Contributor

As fitness professionals, we get plenty of questions about exercise intensity: What is the best intensity to burn fat?  What is the best intensity to improve my running time?  What is the best intensity for recovery?

The answers to these questions, as with most fitness questions, is going to be – it depends!  Of the factors that influence the answers to these questions, fitness level and fitness goals are two of the most important. 

This blog post will provide an overview of some of the general benefits of training at various intensities in terms of percentage of maximum heart rate (%MHR).  We will break down %MHR into five different zones and provide general benefits of training in each zone.  Based on your client’s fitness level and goals, you can suggest which zones are best for them to train in.

First, a definition of the five zones:

Zone 1: 50-59%MHR – A moderate intensity zone

Zone 2: 60-69%MHR – A moderate intensity zone

Zone 3: 70-79%MHR – A moderate to vigorous intensity zone (75%MHR and above is considered vigorous intensity)

Zone 4: 80-89%MHR – A vigorous or high intensity zone

Zone 5: 90%+MHR – A vigorous or high intensity zone

Because it can be challenging for clients to resonate with numbers and %MHR, we recommend using colors to represent each zone.  MYZONE®, the wearable technology company, color-codes each zone so that clients can easily identify with intensity and feel rewarded for their effort.  Below are the colors that MYZONE® uses:

Zone 1: Gray

Zone 2: Blue

Zone 3: Green

Zone 4: Yellow

Zone 5: Red

Zones 1 & 2: 50-59%MHR (Gray) and 60-69%MHR (Blue)

These are great zones for those beginning a fitness program to build an aerobic base.  What does it mean to build an aerobic base?  Improving our ability to take in oxygen and efficiently transport it to working muscles.  Further, our working muscles are developing a greater ability to utilize oxygen to make fuel to support our exercise.  Our capillary (small blood vessel) beds are expanding, and our heart and lungs are getting stronger.

We also burn fat calories efficiently in these zones.  The more fit we become, the more effective we become in using fat as a fuel source.  It is in these zones that we burn the highest ratio of calories from fat (as opposed to carbohydrate or protein).  Please use caution in interpreting the meaning of the previous statements.  The Gray and Blue zones are not the best zones for burning the MOST calories, the Yellow and Red zones are best for that.  If a client’s goal is specifically weight loss related, total calories burned will be the most important factor; however, the Gray and Blue zones will be effective for burning fat calories specifically, so integrating two to three workouts per week in these zones is spot on.

The Gray and Blue zones are good active recovery zones for intermediate and advanced exercisers.  Clients should target these zones in between high intensity cardio or resistance training days.  These zones are also a good target if your client wants to go for a longer duration workout.

Zone 3: 70-79%MHR (Green)

It is in the Green zone that newer exercisers start to expand aerobic capacity to a greater extent and elevate anaerobic threshold.  Anaerobic threshold is the level of oxygen consumption above which aerobic metabolism is supplemented by anaerobic metabolism, causing a sustained increase in lactate and metabolic acidosis.  By elevating our anaerobic threshold, we are increasing our ability to work at higher intensities for longer periods without fatigue.

The Green zone is a good recovery zone for intermediate or advanced exercisers during tempo and interval training.  Tempo training consists of three to five minute bouts of higher intensity work (Yellow and/or Red zones) followed by three to five minutes of moderate intensity recovery (Green zone).  Similarly, interval training consists of 15 seconds to 120 seconds of work (Yellow or Red) followed by 15 seconds to 120 seconds of recovery (Green if possible).

The Green zone is also a good target for a sustained effort (20 minutes or more) for intermediate and advanced exercisers.


Zones 4 & 5:  80-89%MHR (Yellow) and 90%+MHR (Red)

The Yellow and Red zones are short duration zones for new exercisers.  Your clients will probably fatigue fairly quickly in these zones at the beginning of their training experience.  As your clients’ fitness levels build, they will be able to sustain longer periods of time in the Yellow and Red zones.  Perhaps start with short intervals during which your clients push into the Yellow and/or Red zones and then complete a longer recovery in the Green or Blue zones.

For intermediate and advanced exercisers, the Yellow and Red zones are great for challenging fitness level.  Clients can now handle slightly longer durations in these high intensity zones. Challenge your clients to hold the Yellow zone for 10 minutes or more at a time. 

Another approach is to train high intensity intervals during which your clients aim for Yellow and Red during the work phase and Green during recovery.  You can start to lengthen the work-to-recovery ratio of your clients’ intervals.  For example, have your clients push up into the Yellow or Red for 60 seconds, and provide them with only 30 seconds of recovery (a 2-to-1 work-to-recovery ratio).

Training in the Yellow and Red zones is likely to increase your client’s maximal oxygen uptake (their ability to take in and use oxygen efficiently) and expand their ability to work at submaximal exercise intensities for longer periods of time.

As mentioned previously, the Yellow and Red zones are major calorie burning zones – and not just during your client’s workout, but afterward as well.  You may have heard of the term post-exercise oxygen consumption (EPOC).  This refers to the additional oxygen consumption necessary to recover from a high intensity workout – your client will continue to expend calories at a higher rate as they recover from their session than they would generally burn at rest.

Now that you are familiar with some of the general benefits of training at various exercise intensities, use your client’s fitness level and fitness goals to determine the zones that are most appropriate for them.


Dr. Ayla Donlin is the director of the LifeFit Center @ The Beach, a health and fitness facility and educational laboratory on the campus of Long Beach State University (LBSU).  Ayla’s passions are fitness, education, and well-being, and as a result, she holds multiple positions within higher education and the fitness industry.

Ayla is a lecturer in the kinesiology department at LBSU and has been teaching courses since 2008 in the fitness and sport studies options.  She is also the chair of the Exercise is Medicine on Campus (EIMOC) Leadership Team at LBSU and advises the EIMOC student organization.

Ayla has been active in the fitness industry for over 12 years as a group fitness instructor, personal trainer, group fitness director, master trainer, and health club general manager. She is currently an American College of Sports Medicine (ACSM) certified personal trainer and an Exercise is Medicine® credentialed fitness professional. 

Ayla also serves as a consultant within the fitness industry.  She has been working with Johnny G. since 2007 as a Master Instructor for Krankcycle® and became a Master Instructor for IN-TRINITY® in 2015.  Ayla is also a Master Trainer for MYZONE®, a wearable physical activity tracker that rewards effort.  She creates educational content for the MYZONE® blog, Podcast, and learning management system.

As a passion and hobby, Ayla has organized, led, and participated in over 100 hours of Spin-a-thon/Krank-a-thon fundraisers benefitting various organizations like the Challenged Athletes Foundation.

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