Your Heart Rate Monitor is LYING to You

Welcome to the inaugural VTCheck training log, where I will highlight select workouts from my (and perhaps others’) training. This log is not intended to serve as a model for others to follow, as I am slower than an average middle school student. Rather, the purpose of this log is to show users how I, as the person who designed every feature of VTCheck based on an in-depth study of physiological research, use this app to optimize my own training.

Heart Rate’s Major Flaw

The vast majority of endurance training enthusiasts (including users of VTCheck) utilize heart rate to control intensity, so this post is largely against my own self-interests. But the truth is the truth. Having now completed thousands of runs measured by both heart rate and ventilation, I no longer reference heart rate at all during exercise (other than indirectly through the Fatigue metric) and can say with confidence that ventilation is strictly superior to heart rate for both intensity control and fatigue/condition assessment.

To be clear, it’s not that heart rate is useless when it comes to gauging intensity, but it suffers from one major flaw that makes it significantly inaccurate in many situations – heat. When core temperature rises, which it will inevitably do in any workout, blood is pushed to the skin to cool the body down, which increases heart rate independent of metabolic demand.

Now to be clear, both ventilation and lactate readings are also impacted by heat, but the unique problem with heart rate is that it becomes so heavily driven by temperature that it loses fidelity to the most important indicator of endurance sustainability - energy production.

By way of example, after performing nearly 100% of my runs in a small, air-conditioned apartment gym on the exact same treadmill for nearly 10 months straight, I recently joined a commercial gym to use their treadmills so I could track speed in both miles and kilometers. Like many commercial gyms, this location is in a giant warehouse and it tends to get very hot. The following graph depicts a 10x3 session at 7:26/mi pace that I performed at this commercial gym. Notice that the average ventilation is 130 L/min and the average HR is 145 beats per minute, and if you scroll to the last interval, you’ll see that my heart rate gets up to 161 bpm, which is somewhere around the “anaerobic threshold” for my heart rate (despite the fact that my VT2 is 166 L/min while my final interval only reached ~140 L/min).

This next graph shows the exact same 10x3 session performed one week later but 2 seconds faster and at my apartment gym. Here, notice that my average VE was slightly higher than the prior week at 135 L/min, which is what you would expect given the increased intensity. However, my average HR was 133 bpm, more than 10 beats lower than the prior week performed at a slower pace.

Additionally, following are graphs depicting two of my runs on the same day: (a) a 6-minute warmup at 8:13/mi pace immediately prior to the intervals and (b) a 6-minute cooldown at 8:34/mi pace immediately following the intervals. As you can see, for the warmup, my 6-minute ventilation and average HR were 117.8 L/min and 130 bpm, respectively, and for my cooldown they were 114.7 L/min and 133 bpm, respectively. Although the pace for my cooldown was significantly slower than the warmup and consistently tracked by ventilation, my heart rate was higher for the cooldown because at that point, even in the cool apartment gym, my core temperature was significantly elevated.

And there are countless other examples just like this where my ventilation accurately tracks relative to intensity but heart rate fails to do the same. This is because compared to heart rate, ventilation is much more closely tied to what is metabolically happening within the working muscle, which, as described in my last blog, is the most important aspect of exercise intensity.

What this means as a practical matter is that if you use heart rate to, for example, exercise right below a particular threshold in an effort to maximize adaptations while minimizing metabolic disturbance/stress, you may be leaving gains on the table. If temperatures are higher than usual, your heart rate may be following core temperature instead of bioenergetics.

And it is for this reason that I would highly recommend that all heart rate users buy a TymeWear VitalPro, as I believe it will transform your training. To be clear, I am not being paid by the ventilation lobby and I am not sponsored by or affiliated in any way with TymeWear, but the VitalPro, for me, has been without a doubt the most useful device I’ve purchased for my running training (more than my Forerunner 965 or any supershoe) and it’s not even close.