Heart’s Racing: Pushing the Limits In Indoor & Outdoor Cycling

Wednesday of last week I road outside a considerable distance for the first time in a while. I have taken advantage of decent days this winter to for a few extended rides. The fact that I was outside and comfortable for the majority of a day in late February was incredible. I wore bike shorts and a tee shirt in temperatures that nearly reach 80 degrees Fahrenheit. The sun felt warm on my skin. The breeze – of course a headwind – brought me back to how I my summer was spent, tackling a massive challenge crossing the US by bicycle. The thought now does not seem so preposterous, just something to look forward to when an opportunity arises.

After teaching indoor cycling classes for the past eight weeks, it was nice to get outside and ride for myself. I have really come to enjoy instructing indoor cycling classes. Designing classes, motivating people and playing loud music while screaming commands from a small cycling pulpit is a lot of fun. But, this single day of glory in a cold and often overcast winter reinvigorated the soul. The one thing I did notice was that my legs felt a bit gassed after riding hard at each class I teach.

On my late-night return ride home that Wednesday, early Thursday, I was interested to see how my “rides” stacked up: indoor sessions vs. outdoor rides. I currently don’t have a way to measure power on either bike. Nor am I able to calculate distance during indoor classes. What I can compare are heart rate measurements and calories burned, as offered by a Garmin vívoactive HR monitor. After researching heart rate zones and their applications in cardiovascular training, I decided to compare two recent classes and two recent rides.

Disclaimer: The outdoor rides are in NYC where pedestrians, cars and traffic lights take precedence. This is due to safety AND the desire to avoid fines from the ‘Boys in Blue’ (NYPD). Indoor classes  I must hold back to a certain degree as I project my voice over loud music in a crowded room. I could likely push it a little harder personally but would pass out and fall off my bike in a crumpled mess. I have come close a few times…

Below is a chart of Heart Rate Zones  provided by Garmin. I am 33 and 11/12ths so I fall somewhere in between the ranges offered on this website here. Please check out the article to see where your Heart Rate Zones may fall.

Heart Rate Zone

Zone 1

Low Intensity

Zone 2 Moderate Intensity Zone 3 Aerobic Zone Zone 4  Vigorous Intensity

Zone 5

Red Line

% of Max Heart Rate


60-70% 70-80% 80-90%


Graham’s BPM


112-130 131-149 150-167 167-187

In each zone, your body reacts differently to the physical stress or exertions. Here are some descriptions of what happens in each stage. For more in-depth information please reference this article.

Zone 1 – Low Intensity or Healthy Heart: 50 – 60% of Max Heart Rate (MHR)

  • The body derives its energy by burning 10 percent carbohydrates, 5 percent protein, and 85 percent fat.
  • Workout in this zone is less intense and won’t give the most cardiorespiratory training benefits. But studies have shown that it works to help decrease body fat, blood pressure, and cholesterol.
  • Can carry on a full conversation in this zone, although may be breathing a little heavier than usual.

Zone 2 – Moderate Intensity or Fitness Heart Rate: 60 – 70% of MHR

  • In this zone, the body fuels itself with 85 percent fat, 5 percent protein, and 10 percent carbohydrate.
  • One burns more calories per minute than in the healthy heart zone because the exercise is a little more intense. You are going faster and therefore covering more distance. Calories burned will depend effort, or power – measured in Watts, a calculation based on pedal speed and the amount of gear or tension on the bike – plus a few other factors.
  • Same health benefits and fat-burning benefits as the healthy heart zone.
  • Breathing heavier but will still be able to speak in short sentences.

Zone 3 – Vigorous Intensity or Aerobic HR Zone: 70- 80% of MHR

  • The body burns 50 percent of calories from fat, 50 percent from carbohydrate, and less than 1 percent from protein when you are in this zone
  • This is the zone to aim for when training for endurance. It spurs your body to improve circulatory system by building new blood vessels and increases heart and lung capacity.
  • Aiming for 20 to 60 minutes in this zone is believed to give the best fitness training benefits.
  • With the increase in intensity or power, you burn more calories in the same amount of time, as you are covering more distance in that same time.
  • Breathing very hard and able only to speak in short phrases.

Zone 4 – Anaerobic Zone: 80 – 90% of MHR

  • The body burns 85 percent carbohydrates, 15 percent fat and less than 1 percent protein in this zone.
  • This exertion takes the body to the limit where you begin to produce lactic acid.
  • Workouts in this heart rate zone should be in the 10 to 20 minute range or part of an interval training workout.
  • This intense exercise will improve the amount of oxygen you can consume—your VO2 maximum.
  • You will be unable to speak except a single, gasped word at a time.

Zone 5 – Red-Line Zone: 90 – 100% of MHR

  • The top zone is from 90 percent to 100 percent of your maximum heart rate. You can’t go any higher, and most people can’t stay in this zone for more than a few minutes.
  • This zone should only be used for short bursts during interval training, where you work intensely for a minute and then drop back down to a lower intensity for several minutes, and repeat.
  • While you burn lots of calories per minute in this zone, 90 percent of them are carbohydrates, 10 percent fats, and less than 1 percent protein.
  • You will be unable to speak except for gasping single words.
  • You should consult with your doctor to ensure you can work out at such a high heart rate safely.

Now that we know what the zones are and what physical effects each will produce, we can compare what indoor cycling – which is interval heavy- looks like to the steady state outdoor riding, where proper shifting (use of available gears) can keep RPMs even.

Indoor – Feb 13

Indoor – Jan 27 Outdoor – Jan 27

Outdoor – Feb 22

Total Time (hr:min:sec)


0:45:03 1:47:16




663 921


Distance (miles)


NA 20.83


Average HR


148 119


Max HR


179 150


Zone 1 (mins:secs:ms)


0:14:00 18:58:00


Zone 2 (mins:secs:ms)


5:57:00 9:21:00


Zone 3 (mins:secs:ms)


14:08:00 1:06:00


Zone 4 (mins:secs:ms)


22:24:00 0:04:00


Zone 5 (mins:secs:ms)


2:21:00 0:00:00


Screenshot 2018-02-27 21.19.13
February 13 – Indoor Class
Screenshot 2018-02-27 21.15.20
January 27 – Indoor Class
Screenshot 2018-02-27 21.25.31
January 27 – Spirited Central Park Loops
Screenshot 2018-02-27 21.22.43
February 22 – Brooklyn to Harlem Commute


  • Most of the outdoor rides were spent in Zone 2. This is great for weight loss and a pace for riding all day, which I did over the summer. Efforts are casual for training rides. The steady state rides should ideally punch deeper into Zone 3 and maybe reach Zone 4 or 5 at times.
  • Indoor conditions, or lack thereof, offer a rider the opportunity to push harder in short amount of time. Classes are designed to elevate the heart rate into all zones, bouncing back and forth to improve conditioning. A majority of time is spent in Zones 3 & 4 where improvements in cardiovascular and endurance training focus.
  • With the increased effort indoors, the interval training can burn considerably more calories than more casual riding. The January 27th ride was in Central Park and had some hills and sprints, but I only burned an additional 200 calories in an additional hour over the February 13th ride.
  • An ideal training regiment would include 2-3 weekly interval sessions and 3 or more longer outdoor rides to build stamina.

The outdoor rides were more fun or casual rides than actual training. Therefore the Heart Rate Zones and Calories Burned were significantly less. Depending on what you are looking for in personal goals – weight loss, improving cardiovascular efficiency or strength training – each type of cycling has its merits. Outdoors you have views and indoors you have “suffer” as a large group.

With New York being as flat and as densely populated as it is, I haven’t found it practical to complete interval training outdoors. Having moved to Harlem where elevation changes are widely available, as compared to Downtown Manhattan, I plan to tackle harder rides with actual climbs. I will be sure to track these sessions and see how they compare to the more casual outdoor rides and the indoor classes. With the pending Spring and warmer weather, I foresee some better data sets to become available!

Thanks for reading! Please join the mailing list and follow the blog through WordPress or on social media – Instagram and Facebook. Or better yet, join me in person at a class or an outdoor ride!

Please leave questions or observations in the comments section below! I would love to hear from you!

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