Focus Your Efforts with Heart Rate Zone Training

Perhaps this post could be called an ode to the heart rate monitor, my favorite training tool. It gives instant feedback and lets me know how hard I'm truly training, based on my cardiac output. If you're a gym-goer you've probably jumped on a cardio machine and seen this familiar sticker or one of its familiar variations. Why so complicated, cardiovascular machines? I'll explain why one (heart rate) zone doesn't fit all because we all have different training goals.

MHR Chart Based on age

Source

Some machines list 3 target zones: fat loss, aerobic, anaerobic.

Some may list as many as 5: fat burning, aerobic, steady state, anaerobic, maximal.

The division of heart rate zones is somewhat arbitrary, as we only draw energy from 3 different systems. Yet you may see that sticker on the machine and think “I want to lose fat, I need to be in the fat loss zone”. 

“Wow, this is easy!” you might think to yourself 30 minutes later. And it is, because the fat loss zone is typically 50-65% of your MHR (maximum heart rate, sometimes called HRmax). Bust out 30 minutes on your given machine and you might be shocked at how few calories you burn (or how many, as cardio machines are notoriously inaccurate, but that’s another story).

Next time, you work out harder. The machine says you’re in the aerobic, or even anaerobic zones. You burn twice as many calories! But you weren’t in the fat burning zone, so what were you burning? That’s why I’m here.

What is a MHR (maximum heart rate)?

That’s the highest heart rate you can safely achieve through exercise stress, and is dependent upon your age and fitness levels.

Why does it matter?

Working out in the proper heart rate zone is essential to reaching your fitness goals. Note that I didn’t say cardiovascular goals, as you can easily work through multiple heart rate zones when circuit or weight training. The amount of work your heart has to do is proportional to the amount of time you can spend exercising at any given intensity. If you’re working out to lose weight you’ll need to be in a different zone than a soccer player, runner, weightlifter, or yogi.

What are the zones?

The heart rate zones are a percentage of your maximum heart rate.

50 – 60% - The Fat Burning Zone - Ideal for fat loss and building endurance.

60 – 70% - The Aerobic Zone – Utilized to benefit the cardio respiratory system, you’ll become more efficient at transporting oxygen to your muscles and carbon dioxide away from muscles.

70 – 80% - Steady State - Good for weight management and improving cardiovascular fitness.

80 – 90% - Anaerobic – Best for interval training and improving VO2 max. Can cause lactic acid buildup due to lactate being produced faster than the body is able to remove it.

90% + - Maximal – Used for HIIT (high intensity interval training), sprinting, and other quick bursts of energy,

Some machines prefer to divide energy expenditure into 3 categories, as mentioned earlier. In which case the zones would look like this:

60-70% - Fat loss zone

70-80% - Aerobic zone

80%+ - Anaerobic zone

How do I determine my MHR and corresponding zones?

There are two formulas commonly used to accomplish this. I’ll use the example of a 50 year old with a RHR (resting heart rate) of 70. *A resting heart rate anywhere between 60 and 100 bpm (beats per minute) is considered normal.

1. Age-based formula

220 – age = MHR

220 – 50 = 180 MHR

Multiply your MHR by the heart rate % you want to achieve and you’ll determine the zone range.

Fat Burning (50-60%) 90 to 108 BPM

Aerobic (60-70%) 108 to 126 BPM

Steady State (70-80%) 126 to 144 BPM

Anaerobic (80-90%) 144 to 162 BPM

Maximal (90-100%) 162 to 180 BPM

2. Karvonen formula

The Karvonen method calculates the difference between your maximal heart rate and your resting heart rate to arrive at the heart rate zones.

Target HR = ((MHR - RHR) x % intensity) + RHR

I.E.: 125 = ((180 - 70) x 50%) + 70

Fat Burning (50-60%) 125 – 136 BPM

Aerobic (60-70%) 136 to 147 BPM

Steady State (70-80%) 147 to 158 BPM

Anaerobic (80-90%) 158 to 169 BPM

Maximal (90-100%) 169 to 180 BPM

Most cardiovascular machines and heart rate monitors will use the age-based formula to calculate your zones. There are numerous other formulas used to calculate MHR, the most common being MHR = 205.8 - (0.685 x age). However, there are dozen of others that I’m not going to mention for the sake of saving time. 

For an easy Karvonen calculator, go here.

Back to the fat burning zone – should I stay there?

When you exercise you’re primarily drawing fuel from two sources, carbohydrates (glucose) and fat. Picture exercise intensity on a continuum: on one side is fat, that’s what you’ll primarily (but not exclusively) burn at a low intensity via the oxidative energy system. On the other side are carbohydrates fueling a high intensity workout via your phosphagen and fast glycolysis energy systems.

I find this chart helps visualize the process:

At 25% of the VO2 max, the primary fuel source is fat but the energy expenditure (calories burned) is around 75. 75 calories burned in 30 minutes sounds like a very leisurely walk, like strolling down the street to run some errands.

On the other end is the 30-minute run at 85% of VO2 max. The primary fuel source was glycogen, but these people burned ~275 calories.

The goal of weight loss is to create a deficit via calories in and/or calories out. Eat less and lose weight, move more and lose weight, or ideally do both.  The glucose coming from the muscle and liver stores and the fat coming from the oxidative system were both consumed, does it really matter which system is fueling your workout? Not really. Burning more calories wins this round, so amp up the intensity on your cardiovascular workouts to burn more!

What happens if I exceed my MHR?

Your heart will explode.

JOKING! The heart is a muscle and it slowly adapts to the challenges you place upon it, up the ante too quickly and you’ll likely feel fatigued and out of energy due to depleting your glycogen stores. This often happens when people start running after being sedentary for months or years, if you push too hard your heart will have to work too hard to pump blood and you’ll overwhelm your cardiovascular system. The good news is that slow, steady progress will allow your muscles, respiratory, and cardiovascular system to adapt to the stresses being placed upon it.

I’m still confused. What zone should I be in?

That depends on your goals.

1. Are you a short-distance sprinter? Anaerobic, 80%+ of your MHR
2. Running a marathon? Try to average 75% - 85% of the Karvonen MHR
3. Do you like to exercise for ~45-60 minutes at a time at the same pace? Steady pace at 70-80%
4. Short on time? Try cycling through intervals where you do 1 minute in fat burning followed by 30 seconds in the anaerobic zone*
5. Just looking to burn some fat? Walk around, be more active in your everyday life to keep your heart rate low but burn from your fat stores.
6. Enjoy weight training but you don’t burn many calories? You’re likely not lifting heavy enough weights or focusing on isolation-type movements. If strength is your goal, lift HEAVY weights (5 reps max per set) and your heart rate will surely increase. Of course if you’re wearing a HRM during strength training, your focus is likely burning calories. Try any of the following:

• Circuit training. After completing a strength-training exercise, immediately do a cardio burst. Try jumping jacks for 30 reps.
• Swap the bicep curls for push-ups or planks. Work your whole body instead of one muscle.
• Superset your workout. Do two exercises back-to-back to burn more calories.

*Always check with your Doctor before starting an exercise program, especially when working at high intensities and 80%+ of your maximum heart rate.

Need more assistance creating a training plan? Contact me at SeeMeFit for a fully customized 30-day cardiovascular or strength-training workout!