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Stress is Strain: Pt. 2 - Physiological Strain (Heart Rate Training and Lactate)

This article is Part 2 of a series on stress, strain, and load.

In this Stress is Strain series, I'm talking about the different ways we can measure and look at TRAINING stress. Keep in mind, stress and strain from daily life will have a direct impact on some of these metrics. Never discount what is going on in the "real world" and how it affects your training. That's where using the TrainingPeaks comments is super beneficial for your Paragon Training coaches. Reading those comments, we can better understand what you are dealing with on a daily basis (remember the article, "How to Have the Best Relationship with Your Coach"?)

Up this week: Physiological Strain.

Physiological Strain is Stress

This week, I am talking about the second of three categories of stress as strain in training: Physiological Strain (heart rate and lactate).

My favorite—just kidding, it's my least favorite—question I get asked by prospective coaching clients is if I "do heart rate training." My apologies if you were someone that asked that before we started working together ;-). It's an understandable question to ask. A lot of books and coaching methodologies are wrapped up in branding taglines that help identify it. Examples:

  • 80/20 

  • Polarized Training

  • Maffetone Method

  • Heart Rate Training

  • etc.

Diet is much the same way. It's easier to label and sell a product or service if it's got a catchy tagline to it.

The reality is that good coaching pulls from all of these principles and then writes programming specific to an individual's physiological and lifestyle needs.

So where does heart rate fit into training?

In last week's post, I talked about external loads. If pace and power are external, then heart rate and lactate are an internal response to that external demand. Lactate is a little different, since it's technically a fuel source that can be used to create pace or power, but we also use it as a marker of increasing fatigue or exertion, even though lactate isn't creating the fatigue.

The concept here is that even though external load can stay constant the physiological strain on our system changes.

If you've ever gone for an hour run in August in Texas, then you know what I'm talking about. Your heart rate continues to climb, and there's nothing you can do about it. The environment is causing additional stress and the response to that stress is an increased HR. It's HARDER at the end than it was at the beginning and the internal metric shows that. If we only looked at our pace and power, then we couldn't necessarily see that in the data.

Heart Rate (HR) Compared to Pace and Power

Check out this article about Efficiency Factor (EF), which gets a little more detailed, but suffice to say that one way we can track improvement in fitness is by checking what our HR is in comparison to our pace or power. The lower HR you can hold at a given pace, or the faster you can run at a given HR, the fitter you are.

Efficiency Factor Triathlon Training

This is where "Heart Rate Training" comes in. You don't need to let the HR monitor govern your every step, but it is good to know the general ranges you operate in so that you can get a "feel" for how hard you're working. It's an absolute number. The higher the EF, the better.


In fact, one downside to going too hard too often is that we spend a lot of time with elevated HR and thus a lot of time NOT improving our aerobic efficiency. That's a lot of time burning carbohydrates instead of teaching the body to burn fat. A lot of time creating extra stress that may or may not create more "fitness."

Lactate Testing and Training

Lactate is similar in that as you get more fit, you will accumulate less lactate at a given power or pace than you used to. Lactate can be measured through a finger prick and a lactate meter.

I've done a lot lactate testing on myself, as well as the swimmers, cyclists, runners, and triathletes I coach. Looking at how an athlete accumulates lactate at different paces and powers gives me the data to determine their individualized and appropriate zones. Lactate does not cause fatigue but it is an indicator of where the breakpoints of fatigue may occur in a 5k vs a marathon, for instance.

We are now offering lactate testing as a service at the Paragon Training Performance Center. You can do the test while biking on the trainer or running on our treadmill. Read more or book a session below.

Athlete example of why lactate testing is beneficial

You can see the progression from testing in the images below. What I want to highlight is the point at 250 watts. On Test 1, this athlete is at 4.1 mmol of lactate, which is his FTP. After 1 year of aerobic training, he shifted the curve, so that at 250 watts he is now at 1.4 mmol of lactate and his FTP is now 50 watts higher!

So what's the takeaway here?

Triathlon Training in heart rate zones

Let me summarize a few key points on heart rate training we can apply:

  1. Your HR (or lactate) does give a pretty good and unbiased view of how fit you are. It can vary day-to-day depending on hydration, sleep, and weather, but in general, if your HR or lactate is elevated, then you're working hard. Regardless of how you feel or what the watch says.

  2. Getting fitter doesn't always mean going faster in training. The red bar chart above is one example from a "time in training zones" report of an athlete. This athlete's training PACES stayed largely the same from 2019 to 2020. A bit faster on the long runs and of course in workouts, but the easy runs were about the same. What's the difference? Their HR was WAYYY lower at these same paces. They got fitter.

  3. The stress or strain of a workout can vary depending on WHEN we do it and fatigue levels going in. 4x1min hard is way different at the end of a 3-hour ride than after a short 10-minute warm-up.

  4. Improvements in these aerobic fitness metrics will take time and they can come quite frustratingly slow. Maybe even years. That doesn't mean we won't improve or race well during that time, but we may not feel like we're progressing as fast as we'd like. Stay the course.

  5. You don't need a lot to get a good dose of aerobic training. Most people train WAYY too hard most of the time. Be ok training mostly easy and occasionally very hard. This does vary depending on what phase of training you are in and how long you've been in endurance sport.

  6. Don't hesitate to ask and be educated. Our Paragon Training coaches want to help you become more aware of this stuff, so please reach out if you have questions!

Happy training.

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