Well before the advent of GPS watches, the heart rate monitor revolutionized training by providing another window into training intensity. The heart rate monitor has become widely used among athletes, pairing a heart rate chest strap with a watch.
Although many devices today can record heart rate at the wrist using infrared technology, that technology works best for measuring your heart rate at rest — not while engaged in intense activity. If you want to use heart rate as a tool to target training intensity, be sure to use a chest strap paired with your watch. The Coros heart rate monitor arm strap is also a good option.
When undulating terrain and conditions make pace difficult to use, heart rate can prove a valuable tool. It’s the one I most often use along with perceived exertion to monitor my intensity during training. Heart rate is not perfect, though. So it’s important to be aware of its limitations.
Limitations of Heart Rate
Realize that your heart rate will take at least a half minute to respond to any increase in effort level. So don’t expect instantaneous feedback when looking at your heart rate on your watch when starting into a higher intensity interval. This usually isn’t a problem unless you’re doing anaerobic intervals shorter than a minute or two. In that case, you might be running on a track where it would be easier to use time, pace, or power.
Another drawback of heart rate is the phenomenon known as cardiac drift. Over a long duration workout, your heart rate will “drift” upward even if your intensity level — measured by respiration rate, perceived exertion, caloric burn — remains constant. This, in part, has to do with a loss of blood volume due to sweating. Cardiac drift can be mitigated somewhat by staying hydrated, but some cardiac drift is still inevitable. This is a key reason why you should always be tuned into your perceived exertion level based on a host of internal cues, rather than relying solely on your heart rate monitor.
Your heart rate (and respiration rate) will increase at higher altitudes; so if you go to a different altitude to train or race, you should determine your heart rate zones for that altitude.
Your heart rate will also be affected by caffeine. Caffeine, as you know, is a stimulant (which, of course, is why it’s consumed), but stimulants raise your heart rate. Likewise, race nerves and emotional excitation can increase your heart rate by releasing epinephrine and norepinephrine — the hormones behind your “fight-or-flight” response. This is all fine as long as you understand how these factors affect what you may be seeing on your heart rate monitor.
Your heart rate will also vary with your fatigue level. If you’re carrying excess fatigue as you go into a workout, your heart rate will be sluggish to respond when you increase your intensity level during intervals. This can actually be a helpful sign of impending overtraining, illness, or simply a lack of recovery from prior training sessions. If you are unable to elevate your heart rate into the zone you’re targeting for an interval workout; then it may be wise to turn the higher intensity session into a shorter recovery or endurance session that day. Your body is telling you that you need some rest and recovery.
Lactate Threshold Heart Rate (LTHR, or tHR)
Determining your heart rate zones for each of the Alp Fitness intensity levels requires a field test to find your lactate threshold heart rate — abbreviated as either LTHR or tHR.
As with any field test, we’re not directly testing for blood lactate concentration, as would be done in a lab to precisely pinpoint your lactate threshold (LT). Instead, we’re indirectly approximating your LT and are more interested in your effective, or functional heart rate at that physiological point of interest than the precise biomarker itself.