Heart Rate Training For Endurance Athletes
Why Heart Rate Training?
Heart rate monitors are a relatively inexpensive tool that can be used to help guide our training. The old saying "no pain, no gain" is only partially true. Sure, there are times when you need to push yourself into that discomfort zone and it may even become painful (in a good way of course) But the majority of triathletes and endurance athletes should be spending a significant amount of their training developing a solid aerobic base rather than logging copious tempo runs and interval sessions at the track. Yes, these workouts have a time and place but they also have a relatively high cost in terms of recovery. They are best used sparingly during the build and peak phases of training. As triathletes I think we collectively have a problem of being too motivated to push our limits. Chances are even an "easy" run is typically at too high of an intensity to serve the purpose (developing base or recovery) unless we have something to guide us. Enter the heart rate monitor...There is no cheating when that display strapped to your wrist is telling you exactly how hard you are really pushing.

Before we get into the details of HR training zones let's first talk a little about why we should use HR to help guide out training. As I just mentioned above, HR is an objective measure of exercise intensity that we can use to maintain focus during a training session, provide motivation to push hard enough when appropriate, and keep that motivation in check like a tachometer on easier days. HR can also be useful for race pacing and monitoring training load as a sign of potential overtraining. Now I said that HR is an objective measure of exercise intensity and that's not technically true. Our heart rate is actually responding primarily to carbon dioxide levels in the bloodstream and increased oxygen demand as exercise intensity increases. So it isn't directly measuring intensity but it is a reasonable proxy that we can easily measure an monitor. HR isn't really completely objective either. Your HR is subject to lots of other factors that have nothing to do with exercise intensity. Fatigue, hydration, temperature, stress, anxiety, and altitude are some of the more important factors that can influence your HR.

One of the most confusing things about using a heart rate monitor during training is to establish heart rate training zones. Google "heart rate training" and you'll find a lot of different opinions about how to set up training zones. A number of formulas have been developed to estimate training zones based around maximum heart rate…Age-Adjusted Method, Karvonen Formula, Leger Formula, MAF Method…but these formulas are estimates at best and can be 20, 30, even 40 beats off for a given individual. Max HR can be difficult or even dangerous to test for because it requires pushing yourself to the very edge of your limits. Finally, and most importantly, max HR is physiologically meaningless. It tells us absolutely nothing about current fitness or conditioning and isn't something that respond to training.
Lactate Threshold

A much more effective and reliable method for establishing training zones is to base zones around your lactate threshold (LT). Lactate threshold is the highest intensity at which your body can process lactate as quickly as it is being produced and is the single most reliable predictor of endurance performance. LT is highly trainable over years as well as sport specific (likely not the same for run vs. bike). There are a couple of misconceptions about lactate threshold and lactate that I need to clear up before moving on.

First, you may hear the term "anaerobic threshold" used interchangeably with lactate threshold. This implies that there is a point where your body changes to anaerobic metabolism. Anaerobic means "without oxygen" and unless you hold your breath there is never a time when you are not using oxygen. As exercise intensity increases we begin to acquire more and more of our energy from the anaerobic metabolism of carbohydrates but oxidative respiration does not stop. In fact, even sitting at rest your body is producing low levels of lactate. On the other side, most people are surprised to hear that any effort longer then about 2min is primarily aerobic.

Second and third, lactate is typically thought of as a waste product and directly results in lactic acid and the burning feeling you get at higher exercise intensities. In reality, lactate production is a beneficial process that is actually combating acidosis. To understand this we need to examine the basics of lactate production. I don't want this to be a physiology lecture so we're going to keep it very simple and skip over a lot of details. Increased exercise intensity requires more energy in the form of ATP (the basic energy currency of your body). Using ATP produces hydrogen ions (H+) which result in an acidic environment that slows enzyme activity and ultimately breakdown of glucose. Next, carbohydrate metabolism, which also increases with exercise intensity, creates pyruvate. Pyruvate plus hydrogen ions (H+) result in lactate. So you can see that lactate is actually a product of pyruvate buffering hydrogen ions (H+) which are the source of acidosis. You might notice that I didn't mention lactic acid anywhere to this point. That's because your body does NOT produce lactic acid. Robergs et al. (2004) show through detailed chemical reactions that lactic acid is not produced in the body. Don't believe it? Read the entire article online: Biochemistry of exercise-induced metabolic acidosis

As endurance athletes knowing our LT is extremely important for both training and racing. A well-trained athlete can sustain LT intensity for about 60min before overloading their body. Lab testing of LT is the most accurate method for precisely establishing a reference but many athletes either can’t afford this type of clinical testing or don’t have access to facilities with the necessary equipment. Even if you have access to a testing facility, retesting periodically every 4-6 weeks often proved financially and logistically difficult. Some will also argue the applicability of clinical testing to training and racing outside. Lab tests are typically performed on a treadmill or cycle ergometer with a fan to provide cooling. This might not be the best comparison to running or riding the open roads. Luckily, there are ways to estimate your LTHR by performing simple field tests that require nothing more than a heart rate monitor. Many coaches have found that the field test method produce results that are very consistent with lab testing.
Testing Protocol:

Make sure to warm up well for at least 10 to 15 minutes before starting out. The field test is going to be an individual time trial of 30 minutes. The effort should be very hard, but not so hard that you slow down at the end, think race effort of about 10k running or 20k bike time trial effort. For running , unless you have some relatively flat trails or low traffic course, it's best to do this on a track in order to control for hills and avoid changes in effort that could be associated with external factors such as traffic. Another good option is to find a 5k or 8k race (which ever you think would be closest to a 30min all-out effort). If you run a 5k in the 17-22min range then you can also take 95% of your average HR for the race. This can actually produce better results since you have the motivation of the other runners to keep you going. Again, the goal is to go as hard as you can sustain for the entire 30min without slowing and finish with nothing left in the tank.

Start the time trial and make sure to press the start button on the heart rate monitor. After the first 10 minutes press the lap button and then press the lap button again or stop your watch at 30 minutes. Cool down 5 to 10 minutes easy. Your average heart rate over the last 20 minutes is your LTHR estimate.

This same protocol applies to the bike as well. It's important to test both the bike and run because you will likely have different LTHR values for each. As a general rule of thumb, your bike LTHR will be ~10bpm lower than your run LTHR but this could vary from 5-15bpm so it's best to test and make sure. For the bike I think it's even more important to perform the test on a trainer or closed course (think time trial) unless you can find a stretch of road or loop that you can ride hard for 30min without any stops or slowing for traffic and turns. Some people will argue that testing on a trainer isn't ideal (similar to the clinical testing discussed above) because you race and train outside. I agree that the trainer isn't ideal but I believe that the control over your testing conditions and focus you can have on a trainer outweighs the negatives of not being outside. If you do use a trainer be sure to have a big fan directly in front of you to help cool your body and even move your trainer and bike outside if it is cool enough.

Once you've completed your testing and determined your LTHR, all you need to do is enter it in this handy spreadsheet to generate your training zones.