Apple Heart Rate Zone Calculation - Automatic fitness correction

Training Q&A [Moderated]
1

Hi Jordan and Austin,

I just wanted to get your thoughts on the Heart Rate Reserve method that Apple watches use to calculate heart rate zones. I know this topic has been discussed probably ad nauseam but I noticed that my heart rate zones were automatically adjusting based on resting heart rate (fitness) and I wanted to get your thoughts as to whether this is better than a manual input method.

The heart rate zones that Apple uses for Zone 2 for example are not actually 60-70% of max heart rate but calculated using the formula:

Maximum Heart Rate - Resting Heart Rate = Heart Rate Reserve

Lower Bound:

(Heart Rate Reserve x 0.6) + Resting Heart Rate = Lower Bound for Z2

Upper Bound:

(Heart Rate Reserve x 0.7) + Resting Heart Rate = Upper Bound for Z2

Using my measured/estimated numbers on the apple watch:

Max Heart rate = 185 bpm (33 old male, pretty accurate to 208*0.7 + 33), Resting Heart Rate = 59 bpm

Lower Bound for Zone 2 = (126 x 0.6) + 59 = 134 bpm (72% of MHR)

Upper Bound for Zone 2 = (126 x 0.7) + 59 = 146 bpm (79% of MHR)

Apple mentions it updates these numbers on the first of every month and so if my resting heart rate goes down, the heart rate zone thresholds also get lowered. My question is whether these automatically adjusting thresholds make sense as I get fitter?

On my daily morning workouts in Zone 2, I’m currently jogging on the treadmill at around a 10 min/mile pace and I’m wondering whether I should actually be pushing myself a little harder for maximal cardio adaptation and move toward a simple manual 75-83% MHR model?

I know a ton of people use apple watches to measure their training and I’m wondering whether the apple zones are good enough approximation. I am also concerned about injury prevention. I know around the upper bound of the typical 5 zone model for zone 2 is 83% of MHR (154 bpm), that’s a good pace on the treadmill and I’m sure I’ll end up injuring myself at this pace running 5-6 per week like this.

Thank you for enduring another in the weeds post on heart rates!

2

While there isn’t a consensus on what is Zone 2 regarding HR, 70-83% is reasonable, as well as ~ 80% functional threshold, 50% vo2 peak to LT1, and so on. I don’t I do not think you’re more likely to injure yourself running at that intensity provided total training load is appropriate.

I do not think whether or not Apple adjusts your HR zones is going to make a difference in your training stress or adaptations. We’re all just guessing at these zones without lactate measurements, which I don’t think is necessary for most.

3

Thanks Jordan, I’ll continue with the manual adjustments to thresholds and use 75-83% for Zone 2. Hopefully that gets me the best bang for my buck for my 30 min run.

On the plus side to doing cardio every day, I’ve actually seen an improvement in my lifts. My only concern was how much muscle and strength I would lose by pushing my cardio, as well as the potential for an increased risk or injury.

After meeting the exercise guidelines for the past couple of months, I can say for sure that the majority of the population don’t get close to 150-300 mins of moderate cardio. It must be <10%

4

Heh, yep, I would agree with that. I also think that once you realize how little conditioning even “gym rats” get, it’s easy to see the average person gets FAR less than that.