Is that heart rate suggestion kicked out by your tracking tool really helpful? If you’re using heart rate training zones, there are some facts you should know.
In this post I answer:
- What are Heart Rate Zones
- When are Heart Rate Zones Helpful Over 50
- How accurate are predicted Heart Rate Zones
- When HR zones are useful
- How to calculate HR range
- How to use your body to gage your HR zones
I previewed this this blog at this in a recent Instagram post. Here’s a part of that post:
You’re not average. No one is.
The problem with target heart rate calculations is that they imply you are. You are like every other 50, 60, or ______-year-old.
Let me give you a tiny bit of science about HR and then the way you can be sure you’re not over (unlikely for older adults). Full length blog coming this week.
Research on popular formulas for determining Target Heart Rate:
There is poor agreement between measured and predicted HRmax.
That is, measured being that actually testing you during an progressive exercise test, and predicted by doing a calculation using a formula.
Calculating either under and overestimated HRmax in individuals with lower and higher measured HRmax, respectively.
How are Heart Rate Training Zones determined?
A dozen methods of calculating a predicted heart rate have been developed over the years. The one most often used, was developed by Fox et al in 1971. It states HRmax = 220-Age. This is the most commonly used Age-Predicted Maximum Heart Rate (APMHR).
According to research the Fox is 7-12 bpm standard error. Also, according to one of our community members, her recent prediction were almost 20 beats per minute (bpm) under where she actually needs to be. (Based on trackers that have you enter your age and maybe an estimate of your fitness level then give you a heart rate range). I’m currently using a new Garmin that I haven’t added my tested HRs to, and it’s hilariously incorrect with suggestions for me.
Aside from Fox, another method, the Karvonen formula, finds your Heart Rate Reserve first. It is slightly more accurate. There is still room for error (usually underestimating for older adults).
Heart Rate Reserve removes the resting heart rate from predicted heart rate max. This reserve is used to calculate zones then the resting heart rate is added back in. Resting heart rate is an indication of fitness level (in individuals not using a medications altering heart rate).
From the Research: There is poor agreement between measured HRmax and Age-Predicted Maximum Heart Rate (APMHR). The Fox equation may represent the best option for a general population as it is less likely to under or overestimate based on individual HRmax. Individuals should use data from (Graded Exercise Test) GXTs to determine HRmax when applicable to ensure accuracy.
The question begging to be answered is, just who is the “general population?”
And… if “best option” is at least 7-12 bpm standard error? I’m not convinced that “feels like” formula doesn’t have more validity.
This One’s For the Girls:
Gulati and Fairbarn (two researchers) equations were derived for use only in females, as sex differences have been shown to influence the predictive accuracy of APMHR equations. Interestingly, the Gulati formula showed the greatest bias and [error] of all nine equations. In my 38 years of full time fitness, I’ve never been in a setting (clinical or otherwise) where we used a gender-biased formula for predicted calculations. So, while this is interesting, I don’t know of anyone who uses it, in all the lecturing/presenting/consulting/and program leadership and design I’ve done.
It’s those with lower fitness and/or elderly individuals will have HRmax consistently underestimated, and fitter and/or younger individuals will have HRmax consistently overestimated.
Fitness level significantly affects HRmax when comparing individuals of the same age and sex.
Let’s compare using the Fox method of vs the Karvonen method to determine heart rate training rate at 85%. That would be an estimated HIIT work interval level. In this example, I use my age 58 and my resting heart rate as 58.
Step one is to determine the Predicted Maximum Heart Rate or Heart Rate Reserve (Karvonen):
Fox: 220-age (58) = 162
Karvonen: [220-age(58)] – Resting Heart Rate (58) = 104
Step two is to use the 85% for an interval training goal (or higher):
162 x 85% = 137
[104 x 85%] + RHR (58) = 146
Between these two Predicted 85% hear rates, there’s a significant difference. But the most alarming is that measured heart rate testing shows these predicted numbers are a 30 and 20 beats per minute (bpm) underestimation of heart rate at 85%.
Predicted Compared to Measured With Treadmill testing:
85% is where the work becomes anaerobic and not sustainable. You’re breathless and may be able to do 30 seconds or 1:00 but not more. During high intensity interval training your heart rate may also go higher but that is the threshold for HIIT.
When would that be silly to go the the trouble of predicting your HIIT heart rate? Well, a tracker, heart rate monitor is only able to tell you what happened in the past. It’s not telling you what IS true. If you’re focused on the monitor and not on the work, it isn’t a productive session.
One important question we should be asking is:
Is Heart Rate Training Really Best?
For clinical exercise with cardiac rehab or COPD patients, the answer is a definite yes. For endurance athletes’ energy management, training for recovery, and for prevention of overtraining in pursuit of optimal performance, the answer is also yes.
For a midlife woman seeking weight loss, optimal body composition, countering effects of hormonal change, the answer is very possibly and almost always, no, heart rate training isn’t always need. In fact, it can contribute to false sense of success or have her ignore how the exercise makes her feel. Especially if, there’s been no exercise test.
An exercise treadmill test (or bike test if treadmill isn’t possible), should really be used to determine HR zones to be used for HR training. What we need is your Lactate Threshold (LT). It’s the first place you take a deep breath, lungs expand. While testing subjects we watch for this and then watch heart rate spikes to confirm. Then LT 2 is the point where your heart rate no longer rises with the workload increase.
During testing a lot of people don’t reach LT 2 on a treadmill because of other limitations: a joint, inability to move that quickly, fear of the treadmill incline. Generally, they begin holding on and no longer are demonstrating physical capacity. That can limit results, but by that time, a lot has already been learned. An experienced tester can determine zones.
So, what do you do if you don’t have a trainer experienced in GXT or a Balke treadmill test?
BEST USE OF HEART RATE ZONE TRAINING?
When you’re doing recovery workouts and you tend to want to go hard. If you can’t respect the value of recovery and keeping stress load down, Heart Rate Training is best used here! Knowing how to keep your heart rate BELOW a specific point is some of the best use of Heart Rate Zones you have.
We use another method of assessing your readiness for workouts. I wrote about this in You Still Got It, Girl! In the Recovery chapter. Heart Rate Variability (HRV) measures the time between your heart beats. While your resting heart rate, or fluctuation of it can be a good indication of over training or training progress too, HRV, has significantly helped those who don’t know when to rest, do so.
The feedback is less cumbersome than it was 6 years ago. You can get this kind of feedback from tracking tools without the need to don a chest trap first thing in the morning, lay back down and test for a few minutes after you rise.
Whether for athletes or fitness enthusiasts, it’s an extremely valuable too. Healthy recovery has a high HRV score. That is, you want more variable time not less between heart beats to indicate you’re ready to go hard again. Not abiding by the need for recovery, you may be headed for an injury by training again too soon.
When Testing Isn’t Possible or Desirable: It’s OKAY
As exercise physiologists/kinesiologists we use 5 zones for training all kinds of humans. From triathletes to beginning exercisers. Here’s how training zones use activities, breathing, talking, and feelings of exertion collectively to help you know either what your purpose for the workout is or where you actually are:
Zone 1: daily activities of living, nose breathing, talking in full sentences
Zone 2: endurance zone, recovery zone (as well as 1) mostly nose breathing, full sentences
Zone 3: tempo training for runners, higher than comfortable steady state, lower than interval, mostly mouth breathing, choppy between-breath talking
Zone 4: Interval-level, breathlessness, barely talking
Zone 5: Additional intensity, sprint to finish, not sustainable, no talking
Other descriptions of zones
In the literature there are other descriptions, given by other researchers, and I add these not to confuse you, but to be inclusive and relate to information you’ve potentially heard before. These illustrate just a broader application of intensity.
The following percentages will only be useful if you’ve calculated based on an accurate formula or you’ve actually tested and had accurate interpretation put into your personal zones for you.
Low level activity using 30% to 40% of the heart rate reserve (daily activities of life)
Moderate-intensity exercise using 40% to 60% (health benefits)
Vigorous-intensity activity using 60% to 90% (fitness activity)
These broader zones fit the 5 zones in this way:
Low level activity is zone 1
Moderate is still zone 1, low level zone 2.
Vigorous intensity is broken into zones 2, 3, 4, and 5.
The Gray Zone
Zone 3 is what I refer to as “No Benefits Zone.” It’s often an unintended parking place because of a concept called “cardiac drift.” That is when the heart rate for an intended zone 2 workout is allowed to drift higher, and then isn’t managed by decreasing speed or resistance (as in a bike gear). There isn’t more positive training effect by this rise in HR but mistakenly thinking it is, is often the reason exercisers don’t slow down if they “feel fine.” In fact, the intended zone 2 training which is meant for foundation building for new exercisers, base building for endurance athletes, or recovery exercise for anyone, is missed, slowing progress.
The other “misuse” of Zone 3 is when interval training isn’t truly HIIT (or even HIRT). We tend to see instead of the use of Zones 4 & 5 for high intensity work interval and zone 1 for recovery, the murky, not quite high (zone 3) and not really allowing full recovery. The benefits of alternating these are not at all correlated with same fat burning benefit or cardiovascular benefit as HIIT.
If new runners are simply alternating run intervals with walking intervals, this use of zone 3 is harmless. The goal eventually, however, is to have the body adapt such that zone 2 training is where jogging/steady running occurs. For new runners this may not happen right away until a higher fitness level is achieved.
History of Heart Rate Training Zones and Women Over 50
There used to be a reason to discuss heart rate training zones because we thought in the 80s that burning fat happened best below a certain HR. We know so much more about fat burning now that working at low intensities thinking you’re burning more fat is a myth. At least to some extent. As I point out in You Still Got It, Girl!, both high and low intensity exercisers who think they’re burning more fat are “right” when you consider:
You burn a higher percent of fat at low intensity, yes.
You just burn it so damn slow it isn’t helpful.
Sitting down? You burn about 97% fat as fuel right now. How’s that working out for you?
[Now, we also know… if you’re in stress mode, even that is NOT true. You may still be burning mostly carbs or be a “sugar burner” due to the stress. Remember, stress halts fat burning. Stress can be emotional, but also from fasting too long – having the opposite intended effect.]
From an exercise standpoint: the higher the intensity the lower the percent of fat for fuel**.
However, you will be burning calories at a much faster rate during high intensity exercise.
AND… a small fraction of a BIG number… is still bigger than 100% of a very small number.
Read that again.
For example*, Abby walks for 20 minutes vs run for 20 minutes.
She burns 100 calories walking, using 60% fat = 60 calories from fat.
She burns 200 calories running, using 40% fat = 80 calories from fat.
As exercise intensity rises, as in interval training, the gap is more dramatic.
That said, low intensity exercise has benefits. Big Benefits. Removing the obstacle of stress/cortisol is a big one for midlife women. You can’t burn fat by going fast if you’re already under stress. So, the comprehensive decision about your optimal exercise intensity as a midlife woman must consider your current status. In a session with 100 other women blindly following a program of a guru for whom this is working for at the minute, without adjustments for your current hormonal status?
Possible backfire. And…
Drinking 4 cups of coffee a day? Fasting longer than your body prefers? Exercising with inadequate fuel? Emotional stressors in your life? All those combined with estrogen decreases which make cortisol rise, mean you can’t just “zone out” (couldn’t resist!) your training and decide you’ll be more fit if you go harder more often.
What About Heart Rate Training Zones at OC or MyZone?
Even just this week after I’d posted a specific predicted heart rate warning post recently, someone asked if she had calculated her high intensity heart rate correctly.
We have work to do in order to change our thinking. While these calculations once were useful when fitness was born, like we don’t wear our thongs on the outside of leotards and think that’s a good idea anymore… You can’t out-calculate how you feel. Are you breathless? That’s an easy and foolproof method to determine if the intensity is high enough.
By invitation about 4 years ago I tested MyZone at a new club location in Denver as new trainers were doing a “tryout” to demonstrate ability to lead workouts. For those unfamiliar, MyZone is simply a club-based tool for display of heart rate monitors worn by participants. Trainers leading classes or bootcamps may use them as motivation and sources of feedback. They’re intended as a beneficial perk of belonging/attending. But it doesn’t always work in your favor.
The (auto-generated by age) goal heart rate provided for me me was way off my actual training zones (from testing) and using HR training in triathlon training I was well familiar with them. So, I kept getting feedback from the “scoreboard” that was false. Had I abided by it, I would have been under exercising. Others in the small group I observed– all ages though most were younger than I – were struggling to elevate heart rate high enough during intervals – to “please” the arbitrary scoreboard.
You need to understand that unless YOUR zones are tested and plugged into any tracker, using your age to predict will not serve you well. Even adjusting for resting heart rate, though it demonstrates improved accuracy, won’t do you justice.
**It is possible to increase your ability to use fat as fuel at higher intensities. It takes time and specific steps to do so, it’s assisted by testing where your “crossover” point is, the point where you begin shifting to mostly carbs as opposed to more mixed use of fat and carb at lower intensity levels. You can become fat-adapted with slow and low training using fat, and gradually increase intensity while reducing your intake of carbs. It isn’t done by random bouts of exercise or simply not eating or not eating carbs. For midlife women, Low Fuel Availability is something to be avoided. For midlife women, too low or restrictive carbohydrates during periods of regular activity can be stress-inducing however. Again, exactly the opposite goal for many.
What About You? When you calculate your Fox and Karvonen method Heart Rates for Interval training at 85% what difference do you find? Do you use tracking tools to tell you about your readiness for exercise (by Heart Rate Variability score)? Add your comments below. Thanks too for sharing this post if it was valuable.
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Shookster D, Lindsey B, Cortes N, Martin JR. Accuracy of Commonly Used Age-Predicted Maximal Heart Rate Equations. Int J Exerc Sci. 2020 Sep 1;13(7):1242-1250. PMID: 33042384; PMCID: PMC7523886.