How to Use Heart Rate Reserve (HRR%) to Dial In Your Conditioning
When you see Heart Rate Reserve (HRR%) pop up in your training program, you might be thinking:
"Cool...but what the hell is that, and do I need some fancy tracker now?"
Short answer: No.
You don't have to strap a heart rate monitor to your chest (unless you want to). You can get it pretty close just by paying attention to your breathing and how much you can talk. Let’s break it down.
What is Heart Rate Reserve (HRR%)?
Heart Rate Reserve is the difference between your max heart rate and your resting heart rate.
Using HRR% to set your conditioning intensity is more accurate than just guessing based on max heart rate alone—because it takes into account your personal fitness level.
Basically:
If you’re in better shape, your resting heart rate is usually lower.
If you're out of shape (or caffeinated into another dimension), it might be higher.
HRR adjusts for that.
It makes your training zones about you, not about some generic chart taped to a gym wall.
Why We Use HRR% Instead of Just “Max Heart Rate”
The old “220 minus your age” formula?
Yeah… it’s outdated. It works for general ballpark guesses, but it's not great for dialing in smarter conditioning.
Using HRR% gives us:
Better accuracy for setting intensity
Better pacing for building work capacity without burning you out
Better results because you're actually training the right energy systems (instead of always living in that miserable middle zone)
But Here's the Deal: You Don't Need a Heart Rate Monitor
If you have one, awesome.
If you don’t? Your body already gives you all the signals you need.
Here’s the cheat sheet you can use mid-workout:
Simple rule of thumb:
If you can chat, you’re in Zone 2.
If you can only grunt out short phrases, you’re probably hanging in Zone 3.
If you’re making weird gasping sounds? Welcome to Zone 4.
Quick Example: How Conditioning Sessions Might Use HRR%
Base Building Days: Stick to Zone 2. Build your aerobic engine without trashing your body.
Threshold Intervals: Push into Zone 3–4 during work bouts, recover back down toward Zone 2 between.
Max Effort or Fireground-Specific Intervals: Hit Zone 4 for short bursts, then bring it down as fast as you can.
Every session has a purpose. HRR% helps make sure you're hitting it without just guessing or going full send when you don’t need to.
Want to Know How to Actually Calculate Your HRR%?
Here’s how it works if you want to get technical (no spreadsheet required):
Find your resting heart rate (RHR).
First thing in the morning, before coffee or chaos.
Take your pulse for a full minute or use a tracker if you have one.
Estimate your max heart rate (MHR).
Easiest ballpark: 220 minus your age.
(Not perfect, but close enough unless you want to go do a max test.)
Calculate your heart rate reserve (HRR).
HRR = MHR – RHR
Apply the percentage.
Multiply your HRR by the target % (for example, 70% for Zone 2–3 training).
Then add your resting heart rate back.
Example:
40-year-old firefighter
Resting HR = 60 bpm
Max HR estimate = 220 – 40 = 180 bpm
HRR = 180 – 60 = 120 bpm
If you want to hit 70% HRR:
120 × 0.7 = 84
84 + 60 (resting HR) = 144 bpm target
That’s the heart rate you’d aim for in that training zone.
Don’t want to math it out?
Use your breathing and talking as the guide.
Trust yourself—you’re not a robot.
Final Takeaway
Conditioning isn’t just about suffering.
It’s about working the right systems, at the right times, for the right reasons—so you can stay ready for whatever the job (or life) throws at you.
And remember:
You don’t have to overcomplicate it.
You just have to pay attention.
Train smart. Stay ready.
Now get after it.
References:
Swain DP, Leutholtz BC. Heart rate reserve is equivalent to %VO2 reserve, not to %VO2max. Med Sci Sports Exerc. 1997;29(3):410–414.
American College of Sports Medicine. ACSM's Guidelines for Exercise Testing and Prescription, 11th ed. 2021.
Karvonen MJ, Kentala E, Mustala O. The effects of training on heart rate; a longitudinal study. Ann Med Exp Biol Fenn. 1957;35(3):307–315.
Kaminsky LA, Arena R, Myers J. Reference standards for cardiorespiratory fitness measured with cardiopulmonary exercise testing: Data from FRIEND. Mayo Clin Proc. 2015;90(11):1515–1523.
Fletcher GF, Ades PA, Kligfield P, et al. Exercise Standards for Testing and Training: A Scientific Statement From the American Heart Association. Circulation. 2013;128(8):873–934.
