Aerobic Endurance
Power & Heart Rate Zones and Why They Matter
A photo of me on a 72-mile bike ride in the suburbs of Houston about 3 weeks ago.
When I trained for my previous endurance races, I did not know how best to prepare my body to reach peak performance. This year my training looks quite different as I have ambitious time goals to achieve in my four upcoming endurance races.
The San Francisco Half Marathon in 2017 was my first long race. I had no clue how to train for an endurance race, but my former water polo and swimming career had helped me develop willpower to push through pain in order to achieve athletic goals. I brute forced my body into becoming a faster runner; I would run as fast and as long as possible. This strategy (or lack thereof) worked because of my determination to push my body and my competitive spirit. I set the goal to run the half marathon in under 1 hour and 30 minutes, and I just barely hit my goal, clocking a 1 hour, 29 minute time. My knee hurt for 2 weeks after the race, but my foolish 20-year-old self believed that pain was just part of the deal for a long, fast run. Could I have gone faster and protected my body if I trained smarter?
The beginning of the Covid-19 pandemic provided me the time and the motivation to rekindle my interest in endurance racing. I set the goal of running a Half Ironman. A Half Ironman is technically called an "Ironman 70.3" as it consists of a 1.2 mile swim, 56 mile bike, and 13.1 mile run, totaling 70.3 miles. This lofty goal created the exact challenge I needed to rekindle my spirit toward athletic endeavors. As I began to train for this new goal, I once again returned to my "brute force" method: go as fast as I can for as long as I can while training. This method increases speed consistently with enough time and effort, but it is not the most efficient and sustainable way to train. Nevertheless, I proceeded accordingly and notched a very successful race under my belt, completing the Ironman 70.3 in 5 hours, 17 minutes (the time in the photo below is unadjusted for the start delay).
I was very happy with my strong performance in Waco, but right afterward, I had a yearning desire to take my endurance racing to the next level. I began reading much more about endurance training at an elite level. Specifically, a mentor gave me Rich Roll's book, Finding Ultra (which I highly recommend and Rich Roll now has a podcast). The book taught me that my training strategy was not the optimal one for peak performance. I learned from Roll's story that the foundational training for endurance sports should be done at much lower intensity.
Racing for multiple hours uses incredible amounts of energy, and our bodies produce energy in 2 ways: aerobically and anaerobically. Aerobic exercise primarily uses oxygen that we breathe to provide the energy to our muscles while only using small amounts of the glycogen stored in our cells. Anaerobic exercise taps into those glycogen reserves, and this energy production process causes our body to produce lactic acid and to fatigue. Aerobic exercise is much less fatiguing, so the best endurance athletes try to utilize aerobic energy production for as long as possible during a race.
How do we know when our body changes from aerobic to anaerobic? The key marker is our heart rate. Usually what's called the "aerobic threshold" is the heart rate threshold at which our body will change energy modes. The number of this threshold depends on max heart which varies by person and age; the number is usually around 75 percent of one’s max heart rate. My max heart rate is about 198 beats per minute so my aerobic threshold is just under 150. I am providing estimates because I never have tested my exact max heart rate. I only know the number that my Whoop has estimated for me.
In the Waco race, I ideally would have kept my heart rate under 150 for most of the race, but I did not. Perhaps, I would have improved my time significantly if I had known to train and to race smarter. As my training has ramped up over the last 2 months, my focus on aerobic training has been the priority. The focus on aerobic training will be especially important to prepare me for the grueling 110-mile Triple Bypass bike race in Colorado, which will involve 8 or 9 hours of continuous exercise.
Specifically, I have been doing an 8-week program on the Peloton called "Peak Your Power Zones" that has provided a structure for my aerobic training. The program involves 3 sessions per week—two 45-minute rides and one 60-minute ride. Each ride is focused on training at different intensity intervals called "Power Zones," which are a range of Watt outputs that you generate biking. The Watt output number depends on the cadence and resistance of your pedal strokes that the rider sets on the bike. Riders have different power zones specific to their fitness level, and a Functional Threshold Power ("FTP") test can calculate one’s power zones. The test involves a 20-minute session to reach a maximal average Watt output, pushing the body to its physical limits to determine a baseline. When I did the test in early May, my average Watt output was 250 for the 20-minute test, and I was exhausted at the end.
An example of the Power Zone display on the Peloton. These are not my numbers, haha…
The goal of the program is to raise this number considerably over the course of 2 months. I still have a week until I test again at the end of the program, but my progress is clear. On Monday during one of my 45-minute rides, I averaged 264 watts. Not only was that ride more than double the length of the FTP test, but also, I was not nearly as exhausted when completing that longer ride. I am very excited to see how much I end up improving my FTP soon.
The program has created this dramatic improvement by primarily doing intervals focused on Power Zones 2 and 3, which are aerobic training zones. Below is a breakdown of the seven Power Zones and my Watt output ranges for each. When I update my FTP test at the end of the program, my Watt ranges for each zone will raise significantly:
Zone 1 – 1 - 140 Watts | This zone is very easy and does not raise heart rate very high. Zone 1 is easy enough that it would not noticeably improve cardiovascular fitness.
Zone 2 – 141 - 191 Watts | This zone requires easy to moderate effort but at a level where you could maintain the effort all day. Zone 2 is the easier of the aerobic zones.
Zone 3 – 192 - 229 Watts | This zone is moderate intensity that could be maintained for a few hours. Zone 3 is the more intense aerobic zone, approaching but not yet reaching anaerobic exercise.
Zone 4 – 230 - 267 Watts | This zone is high intensity that could at maximum be held one hour. Zone 4 is called the "threshold zone" because you are holding an output right around the aerobic threshold, and the body is beginning to tap into anaerobic exercise.
Zone 5 – 268 - 305 Watts | This zone is very high intensity that could at maximum be held for about 15 minutes. Zone 5 has pushed the body fully into anaerobic exercise, which is why this intensity can only be held for a short duration.
Zone 6 – 306 - 381 Watts | This zone is extremely high intensity that could at maximum be held for about 5 minutes. Zone 6 is an even greater effort pushing the body even deeper into anaerobic exercise.
Zone 7 – 382+ Watts | This zone is an all-out, maximal intensity that could at maximum be held for about 1 minute. Zone 7 is the absolute most energy output your body can handle for a short sprint burst.
Each Power Zone also correlates to my five Heart Rate Zones, which I include below. Unlike my the Watt ranges for my Power Zones, the number ranges for my heart rate zones will not change over time:
Zone 1 – 1 - 119 beats per minute (bpm) | Less than 60% of my max heart rate, which correlates to Power Zone 1
Zone 2 – 120-136 bpm | 60 to 70% of my max heart rate, which correlates to both Power Zones 2 and 3. This heart rate zone is fully aerobic.
Zone 3 – 137-155 bpm | 70 to 80% of my max heart rate, which correlates to both Power Zones 3 and 4. This heart rate zone includes my aerobic threshold level, thus a blend of aerobic and anaerobic.
Zone 4 – 156 - 175 bpm | 80 to 90% of my max heart rate, which correlates to both Power Zones 5 and 6. This heart rate zone is fully anaerobic.
Zone 5 – 176+ | 90 to 100% of my max heart rate, which correlates to Power Zones 6 and 7. This heart rate zone is the absolute maximum my heart rate can be pushed.
The Heart Rate Zone display on the Whoop app. These are my numbers!
Now that I am deliberately focusing on my aerobic fitness, my confidence that I will reach peak performance in my races this year is growing. My cousin Warren, who is doing the Triple Bypass race with me, and I completed two very long rides during June, demonstrating my progress. First, we did a 72-mile ride in one of the suburbs of Houston. The following weekend we did an 82-mile ride in Waco. Both rides concluded as the Texas summer heat began to become a factor, so overcoming the heat after hours on the bike were big training accomplishments. Not the same challenge we will meet in the Triple Bypass, but perhaps the Texas summer heat will be a passable training substitute for the Colorado altitude and mountainous terrain.
During July, I will focus more time on higher intensity workouts dedicated to improving speed, but I will maintain a majority of my training time on aerobic endurance. In a few weeks, I will give another update on how these and other metrics are improving and on more of my experiments to optimize my fitness and health.