Thursday, September 1, 2011

Training in Heart Rate Zones

Many moons ago I mentioned that I had a VO2 max test done, and I frequently  mention about "staying in Zone 2" during long runs and rides. Several commenters asked me to explain what that means so here is a very brief overview.

Earlier this spring I had what is called a Vo2 max test- this is a maximum effort test that tells you your heart rate training zones. The test itself was pretty grueling. My bike was placed on an indoor trainer and I wore a face mask that measured the amount of oxygen I was exhaling. The tester made the effort on the bike harder and harder until I could not go anymore. It started off easy and finished super hard- to the point where my heart was about to pounce out of my chest, I was dripping sweat all over the floor, and my legs were burning. It was fun.

scary looking, right?

What the machine is measuring is how much oxygen I am consuming as the effort gets harder. We need oxygen flowing to our muscles to prevent lactic acid build up- this is called being aerobic. When there is little or no oxygen flowing to the muscles the muscle cells use reserve energy and this is called being anaerobic.

There is a point where the oxygen consumption plateaus even if the effort increases- this is your Vo2 max. It is at this point where you would not be able to exercise much longer. And truth be told, if I had to keep pedaling my bike at max effort for 30 more seconds I would have lost my lunch on the floor. This is why they tell you not to eat for a few hours before the test.

After the test was completed the machine printed out a nice little chart that showed my heart rate zones. Let me explain the different zones:

Zone 1: This is the active recovery zone. Think of an easy jog or a Sunday stroll on your bike. This zone triggers growth hormone release but it is not intense enough to increase damage from previous hard work outs.

Zone 2: This is where all of the long runs and rides take place. This is the aerobic threshold zone- the zone where your muscles are getting the maximum amount of oxygen. In this zone you burn mostly fat and not as many carbs. Training in this zone activate the slow twitch muscle fibers which is what you need for long endurance events.

Zone 3: For me, my Z3 feels very much like Z2. You are still getting oxygen to the muscles but you are doing more damage to the muscles and will require more recovery. In this zone, more carbs start being burned than fats. Not too much training is done in this zone.

Zone 4: This is called the lactic threshold zone. Both the aerobic and anaerobic systems are working together to provide energy to the muscles. This is what tempo runs and speed work are done at in order to increase your lactic threshold.

Zone 5: This is the zone were your body cannot get rid of the lactic acid as fast as it is producing it. Training in this zone has its benefits of increasing endurance performance but the recovery time is high due to the lactic acid build up in the muscles and the blood.

Heart rate training can also be extremely frustrating. When it is warm outside, or if I am slightly dehydrated, or tired, I feel like my Zone 2 is super slow. I have noticed that during my long rides and runs if I dedicate myself to staying in Z2 I wake up the next morning with fresh legs where as when I push into Z4 or Z5 during track practices, I can barely walk.

I think heart rate training is really important for long events such an Ironman. I also suggest getting a Vo2 max test done if you can because my perceived effort compared to my actual heart rate zones were way different!

I had my test done by Melissa Dalio of Endura Coaching. I really enjoyed my experience with her. After the test she walked me through all of the results and even told me how many calories of fat vs carbs I was burning, which helped me dial in my nutrition for the long training sessions. Reach out to me if you want her information!

Hope this helped explain what I mean when I say Z2!


  1. I definitely need to have this done - I think my training needs an overhaul, and this is Step 1 - thanks for the post Lauren!

  2. I just had my VO2max tested with Melissa on Tuesday!!! When I saw your picture I was like 'I know that basement/studio!' She is really great, and explains so much. I had been training in HR zones, but they were calculated online and were totally off, so it was great to get the 'real' ones.

  3. I think all this HR stuff is pretty fascinating since I know very little about it.

  4. I just purchased a Vo2 max test too! I was thinking I would do the running test but I can't decide. I am doing Ironman CDA in June and I'm definitely weaker on the bike but I would rather know my run numbers.... I can't decide! Any thoughts? Why did you do bike?