The middle-aged athlete part two: being a guinea pig for heart rate experiments

Sometimes I like treating myself like a guinea pig.

My recent experiments on myself involved using a heart rate monitor watch for the first time. I learned about the physiological basis of running training decades ago, but as an elite runner I was never actually tested to find out my maximum heart rate or VO2max. Besides, it’s one thing to know the theory of exercise and another thing to be able to observe how one’s own body responds during everyday workouts. I wondered if I would learn anything new about my heart, its response to exercise, and the way I pace myself during running or cycling.

How to read this post

Just a warning: there is nothing new or earth-shattering in this post. I’ve included some details about heart rate training zones below for those who don’t know much about exercise physiology or how these training zones are calculated.

People who already use heart rate monitors will be very familiar with the kinds of heart rate graphs shown in this post (taken from my Garmin Connect website). The main purpose of this post is to share my attempt to estimate my maximum heart rate from a few near-maximal workouts, and to show people unfamiliar with heart rate monitors the kind of data and graphs they can provide.

How do you know what your maximum heart rate is?

The general formula for estimating maximal heart rate (HRmax) is 220 – age, but I was sure mine was higher than this. By doing some research online, I discovered that there are several other formulas that are more accurate than the simple age one. However, they don’t all give you the same answer.

You can also get tested in a lab setting to find out your HRmax. In such a test, you will run on a treadmill or ride a stationary bike for around 20 minutes (until you can’t keep going) at increasingly intense levels (i.e. treadmill grade and speed increased, bicycle resistance increased). A simple test I read about on a website is probably also pretty accurate: this website advises you to “run a mile as fast as you can and try to read your heart rate off your watch before you throw up.”

I didn’t want to do the mile test because I knew an all-out mile wouldn’t be good for my knee (no other excuse, I swear!). I was hoping my Garmin would give me an indication of how hard I can push myself in various activities: running, cycling (on a mountain bike), and indoor workouts on a stationary bike and an Arc trainer. I hoped that by pushing myself to near maximal levels in several activities (but not running), I could estimate my HRmax.

Since I’ve always had the ability to “feel” the level of exertion that I can sustain for a given time, I wondered whether my subjective judgment of exercise intensity would be accurately reflected by my heart rate. Before I tried the heart rate monitor, I would have said that the hardest workouts I do now are my Arc trainer workouts. These workouts are usually only about 20 minutes long, and I often include eight minutes of intervals where an all-out one-minute “sprint” alternates with an easier minute. I can’t push myself anywhere close to all-out on my 5K training jogs because my arthritic knee is too uncomfortable and I fear the after-effects.

First experiment: comparing heart rate during different types of aerobic and mixed aerobic/anaerobic exercise:

1)     100-minute mountain bike ride including large and small hills

2)     Steady to intense 22-minute Arc trainer workout with “sprints”

3)     Moderate to intense 21-minute stationary bike workout

4)     Easy to moderate 24-minute run

All workouts except the first one are short; my knee doesn’t allow me to run longer than about 25 minutes without getting sore and swollen; and my cardio machine workouts reflect my preference for working out efficiently on boring machines by doing short but intense workouts.

I expected that all my workouts except the run would allow me to get a good estimate of my maximum heart rate since I planned to push close to all-out on portions of my machine workouts, and my mountain bike route included one long, steep hill that I knew would push me to my limit.


Workout 1: 100-minute bike workout with one giant hill

Highest heart rate: 166 bpm

heart rate graph from a long intense bike ride

Heart rate during a 100-minute bike ride with a big hill climb in the middle

Workout 2: 22-min Arc trainer workout

Highest heart rate: 172 bpm

heart rate graph during a gym workout with Arc trainer, rowing machine and weights

Heart rate during an Arc trainer workout with sprints (22 min with easy 90 sec at end) and other gym activities

heart rate graph showing heart rate during a stationary bike workout

Heart rate during a 21-minute stationary bike workout with increasing resistance (one minute easy plus four minutes rest at the end).

Workout 3: 21-minute stationary bike workout

Highest heart rate: 168 bpm

Workout 4: 24-minute run in Mundy Park

Highest heart rate: 164 bpm

heart rate graph of 5K moderate run

Heart rate during an easy to moderate intensity run with gradually increasing speed

Discussion: any surprises?

I was impressed by the consistency of the heart rates my Garmin reported during the hardest portions of my long mountain bike ride (166 bpm), stationary cycling (168 bpm), and my Arc trainer workout (172 bpm).

During my short stationary bike workout, I started with a low resistance to warm up, but increased the resistance steadily, and this increase was reflected by a continuously rising heart rate. By 15 minutes into the workout, my effort felt very uncomfortable; by this time my heart rate was over 160, and with a slight increase in resistance during minutes 18 to 20, I was in extreme distress with my heart rate reaching a peak of 168.

On the Arc trainer, I again started with an easy effort to warm up, increased my effort steadily during the first twelve minutes, then did a minute at a reduced speed before starting the “sprint” portion of my workout. This consisted of four sets of one minute “sprinting” (except I made it 90 seconds for the last one) during which I increased both the resistance of the machine and my speed, followed by a minute “easy” with lowered resistance, speed, and my arms resting instead of pushing the bars. During this workout, my heart rate reached 156 at the end of my 12-minute steady section. At the end each of the four “sprint” sections, my heart rates were 165, 168, 169, and 172. (I can add that when I took my arms off the machine after the last hard 90-second burst, I almost fell off because of fatigue.)

I felt that these results agreed with what I felt subjectively: during the hardest parts of these workouts my exertion was near 100% and physically I was in great distress. Perhaps I could reach the higher heart rate on the Arc trainer because I was standing, and I was using my arms as well as my legs.

Not surprisingly, my run was too easy to push my heart: near the end of my run my heart rate reached a maximum of 164 bpm. I started this run extremely slowly and increased my pace gradually during the first 2K. I was running in Mundy Park, which has some small hills, so this caused ups-and-downs in heart rate which were accentuated in my case since my knee allows me to push hard on uphills but forces me to run downhills slowly.

However, what surprised me about my running heart rate profile was that even when my heart rate reached the 160s, I didn’t feel I was exerting myself more than moderately; I was fully in control and enjoying my run. This was strikingly different from my mountain bike results, where I felt like I was struggling and making a huge effort as soon as my heart rate got into the 150s or higher. I attribute this subjective difference in effort to the fact that my legs aren’t strong; that appears to be my limiting factor in cycling uphill. I also have a circulatory problem in one leg that limits its strength endurance (see my previous post).

Even on the Arc trainer, which like running uses both arms and legs and is weight-bearing, exercise with my heart rate in the 160s felt harder than running at an equivalent heart rate. Perhaps this can be attributed to the sheer boredom and artificiality of the machine, while running, especially in a forest, allows one to experience many pleasant distractions and sensations.

Another surprise for me was noticing that a small change in heart rate can be felt subjectively as a huge change in exertion. So for example, when my heart rate was 160 on the Arc trainer, I was making a good effort, but not to the extent that I was suffering significantly. Yet at 166 or 170 I was in acute distress, knowing I could maintain such a pain level for only a very short time. Similarly, on my mountain bike, riding with my heart rate in the 140s was pleasant, but I was pushing my legs very hard once my heart rate reached 155.

In fact, I wouldn’t have been surprised by the way perceived (and actual) effort increases dramatically with a small increase in heart rate if I had remembered my exercise physiology. As I explain in the section below, what was happening was that during the hardest parts of my workouts I was shifting from aerobic to anaerobic forms of energy production. This involves a painful effort that cannot be maintained for long.

In addition, it takes the body some time to recover from anaerobic efforts. That explains why, during the “interval” portion of my Arc workout, my heart rate only dropped by about 10 bpm during each “easy” minute following my all-out “sprints”. Those sprints were intense anaerobic efforts, and I couldn’t recover from them in a minute of easy activity resembling jogging.

This is why, during track workouts, it’s critical to understand the purpose of the workout and know how to pace multiple repeats with a designated rest.  For example, when doing a workout of 10 x 400m with one minute rest, the pace of the first few 400s may feel fairly relaxed, but it is fatal to do these first ones too fast. A one-minute rest doesn’t allow one to recover from a near-maximal effort. Also, my Arc trainer heart rate data suggests that taking a rest by stopping completely after each 400m would allow the heart rate to come down more rapidly than by taking a jogging break.

I found it fascinating to gain insight into my own physiology by looking at these heart rate graphs. I have used this data to estimate that my HRmax is somewhere around 180 bpm. This is based on knowing that I could push slightly harder on my Arc and stationary bike workouts, and much harder in my running workouts if I ignored the pain in my knee.


Basics of exercise physiology

I’ll try to explain the physiology of exercise very simply. When a person is exercising, oxygen is used to produce ATP (adenosine triphosphate) which supplies energy to his working muscles. As exercise intensity increases, the muscles need more and more energy, and they reach a point where they can’t get enough ATP through aerobic (using oxygen)processes. At this point the body shifts to an anaerobic (without oxygen) process of energy production. The downside to this is that it results in the production of lactic acid. Lactic acid is a metabolic poison that, as it accumulates in the muscles, paralyzes them and forces the athlete to slow down or stop exercising to allow the lactic acid to be carried out of the muscles.

The point at which a person stops getting all their energy needs met by aerobic metabolism is called their anaerobic threshold (AT). This point is generally reached a person’s heart rate is between 80% and 90% of their maximum heart rate.

At this point, the person is using the maximum amount of oxygen their body is capable of using. This is called their VO2max (also known as maximal oxygen consumption, maximal oxygen uptake, or maximal aerobic capacity). It is usually expressed in mL/kg.min (to account for a person’s body weight).

VO2max is usually determined in a lab setting by making a person run on a treadmill while gradually increasing the grade and speed of the treadmill. Equipment is attached to the athlete to measure their consumption of oxygen and production of carbon dioxide. Blood samples are also taken throughout the test. When the person’s oxygen consumption reaches a steady state even when the intensity of the exercise is increased, their VOxmax can be calculated. Elite athletes, particularly cross-country skiers and runners, typically have high VO2max values—males up to 85 and females up to 77. VO2max is partially hereditary, but can also be improved with training. It is a strong determinant of endurance during prolonged, sub-maximal exercise. However, in running, for example, VO2max isn’t the only thing that determines performance; other factors include a person’s running economy and their mental and physical resistance to fatigue.

Training zones based on heart rate

Many training programs will advise you to train within different training “zones” based on your goals and what type of training effect you are trying to achieve. Most training programs will advocate working in a variety of zones ranging from easy (for “rest” days or achieving aerobic base fitness) to intense (to increase speed endurance and pure speed). Heart rate training zones are based on your individual heart rate values: your maximum heart rate (HRmax), your heart rate at rest (HRrest), and your heart rate reserve (HRreserve), calculated from the simple equation below.

HRmax – HRrest = HRreserve

You can find out your HRmax by getting professionally tested (on a treadmill or a stationary bike), or by using various equations to estimate your HRmax. The best time to determine your resting heart rate is to take it first thing in the morning before you get out of bed.

Heart rate zones are given as percentages based on the Karvonen formula, a simple equation that uses the heart rate values explained above. For example, to calculate your 80% level, do this equation:

HRreserve x 0.8 + HRrest = HR (in bpm)

For example, I have measured my HRrest as 48 bpm. I estimate my HRmax to be 180 bpm (based on my training experiments with a heart rate monitor and some sample calculations following equations for estimating HRmax).

Therefore, my HRreserve = 180 – 48 = 132 bpm.

My 80% training level is (132 x 0.8) + 48 = 153.6 bpm.

If I wanted to train in what is usually called the anaerobic or threshold zone (between 80% and 90%), I would also calculate my 90% heart rate.

(132 x 0.9) + 48 = 166.8 bpm.

Then, using a heart rate monitor, I would try to keep my heart rate between 153 and 167 bpm.

Training Zones

Most training systems that use heart rate zones give five zones based on heart rate percentage calculations like those explained above. It’s better to know your own individual heart rate zones rather than relying on generic tables based on “average” maximum and resting heart rates.

Here are the five zones and their training purposes and effects:

Table showing heart rate zones for exercising

For more information on heart rate monitors and how they can help you please view my posts about Garmin and Polar watches and their coaching features.

About nancytinarirunswrites

I used to be known as a competitive runner, but now I have a new life as a professional writer and editor. I'm even more obsessive about reading, writing, and editing than I was about running. Running has had a huge influence on my life, though, and runner's high does fuel creativity. Maybe that's why this blog evolved into being 95% about running, but through blogging I'm also learning about writing and online communication. I'm fascinated by how the Internet has changed work, learning, and relationships. I love to connect in new and random ways!
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