B Strong. B Fast. Just Fit.

Training Intensity Zones

Published March 27th, 2009 in BAMFing, Training Science

I know you’ve heard the sayings, “there’s always someone out there training harder than you,” or “you have to work harder than the next guy to win,” etc. It all sounds like something you remember from your old grade school gym teacher, or football coach. In fact, many people and coaches are still using these sayings to try to motivate themselves, or their athletes today. While it’s true that you have to train hard and be dedicated to succeed, training harder all the time doesn’t usually equate with better results, and can oftentimes lead to injury, or burnout.

This is where I throw out another famous saying, “train smarter, not harder!”

As much as I like training, I would still much rather train less if my return from those extra miles, or extra reps is only negligible at best. I want to get the most return on my investment, which for me is my time and my effort.

So what does “training smarter” mean? It means understanding how to train at the appropriate intensity to get your desired results. This is crucial for the endurance athlete. Training too fast all the time, will never help you go farther and training too slow all the time, will never help you get faster, or stronger.

One of the easiest and most widely used methods of measuring intensity is to monitor your heart rate. The faster or harder you work, the higher your heart rate will be, and vice versa. It sounds simple enough, but at what heart rate should you be training at to get the most out of your workouts? The answer depends on what you are trying to achieve. Depending on your goal for the workout, there is a specific intensity zone you should train in. These zones are delineated by specific heart rates, and determined by your lactate threshold.

Before I discuss the different training intensity zones, it is important for you to understand what the lactate threshold is. Your lactate threshold, or LT is the point at which your body goes from training aerobically (with oxygen), to anaerobically (without oxygen). At low levels of exercise, your body is able to create energy by breaking down fats and carbohydrates. The breakdown of carbohydrates produces lactic acid. At these low intensity levels, the body recycles the lactic acid easily to create more energy for your body to use. As intensity increases, lactic acid continues to build up and be recycled, until the point at which it accumulates faster than the body can clear it and the build up begins to inhibit muscle contraction. This is called the onset of blood lactate accumulation (OBLA), or your lactate threshold. At this point the body is going to rapidly fatigue and the duration of exercise will be short.

Knowing at which intensity, or for our training purposes, heart rate, the LT occurs is vital to setting up proper training intensity zones. Below I describe 7 different training zones. They are based on the model by renowned endurance coach Joe Friel. I have also added the percentage of lactate threshold heart rate at which these zones occur.

Zone 1 -Active Recovery 65-81% Threshold Heart Rate

As the description clearly says, this zone is for recovery purposes, and for early fitness building. This is also the zone used as the active rest portion of interval workouts. Workouts in this zone are meant to be easy to enable the body to recover from harder training sessions.

Zone 2- Aerobic/Extensive Endurance 82-88% Threshold Heart Rate

This is where those long duration sessions are most commonly done. It is used to build aerobic endurance and help the muscles become stronger and better able to use oxygen for energy production. Your slow-twitch muscle fibers are doing the majority of the work.

Zone 3 -Tempo/Intensive Endurance 89-93% Threshold Heart Rate

This zone is used for early season tempo work and to begin LT improvement. It helps to build base endurance and incorporates more fast-twitch muscle fibers as support for the work of the slow twitch fibers.

Zone 4- Sub Threshold 94-100% Threshold Heart Rate

As you may have guessed from the title, this zone brings you just under, or right to your lactate threshold. Its purpose is to stress aerobic capacity and challenge energy production. Intervals, hill work, and tempo work are all common sessions in this zone to help increase muscular endurance and threshold speed.

Zone 5a – Super Threshold 100-102% Threshold Heart Rate

This zone is used together with Zone 4. Intervals, hills, and tempo sessions are used to improve lactate tolerance and removal, as well as the fast-twitch fibers conversion to slow-twitch characteristics. You are now working anaerobically, so training duration will be decreased.

Zone 5b – Anaerobic Endurance 103-105% Threshold Heart Rate

Now working exclusively anaerobic, the body’s ability to tolerate and remove lactate is severely stressed. Fast-twitch muscle fibers are used to provide a large amount of the work at this level. Intervals and hill work to improve anaerobic endurance will have a work to rest ratio of 1:1.

Zone 5c – Neuromuscular Power 106%+ Threshold Heart Rate

Zone 5c is fast. For the endurance athlete, its use is limited to possibly a final sprint, or to make a pass. It can only be maintained for a few seconds, and intervals are paired with long recoveries.

Now that the training intensity zones are clearly defined, there’s still one issue. How do I discover my lactate threshold?

There are a number of different methods, and each involves a test of some sort. If you have access to a lab at a sports center, or university, you can get a maximum capacity test whereby they will measure your carbon dioxide to oxygen gas exchange difference using a breath analysis machine to help determine your LT. Another way which is gaining popularity is to perform a max test and actually have blood drawn from your finger at regular intervals to measure the blood lactate levels at different intensities. This one is obviously more invasive. For those of you who do not have access to either of these methods, you can perform a time trial running and on the bike to give yourself an estimate of your LT for each discipline.

I will describe how to perform these time trials in another article, and include a “Zone Calculator” to more easily figure out your specific intensity zones.

No matter which method you use, knowing your LT is important for setting up your specific training zones and planning your training for the season.


Click here to download a Heart Rate Zone Calculator