When I talk about zones, it is the difference between intensity of exercise that determines these zones. In most cases, we use heart rate to determine the zones. These Zones are numbered 1 through 5, or sometimes given names like, Recovery, Endurance, Tempo, Threshold, SuperThreshold, and Maximum output for example. While training for sport, all the different zones are necessary for performance improvement, Zone 2 training is by far the most important part of the endurance training program. The purpose of each training zone is to elicit specific physiological and metabolic adaptations in order to improve performance, and it's important to know what physiological and metabolic adaptations occur while in each zone and how they can be improved in training.
To understand this, first we need to have an understanding of basic physiology and muscle metabolism. Through our 3 main energy systems we can train for all types of activity. Let’s break it down.
Energy Systems
Three energy systems contribute different amounts towards re-synthesizing the compound Adenosine Triphosphate (ATP), the "energy currency" of our body. With the help of our mitochondria which processes ATP, our muscles make the contractions for movement. The main energy system we utilize depends on the intensity, type and duration of the exercise being performed, as well as the fuel sources available and the fitness levels of the individual. These systems are also dependent on whether we use oxygen (aerobic) or not (anaerobic). They are:
1. The ATP-CP System (Anaerobic): lasts up to about 10 seconds of very high intensity efforts. An example of this would be doing an explosive Olympic lift, or a 100 meter sprint. The ATP-CP system uses a stored molecule in the muscle called creatine phosphate (CP) to resynthesize ATP. It is the breakdown of this molecule that releases the energy needed to rejoin the ADP and free phosphate to form ATP. This system is anaerobic as it works without oxygen, and does not produce any waste products. This is Zone 5 & 5+
2. The Lactate System (Anaerobic): is the active system used from 30 seconds to 3 minutes of high intensity efforts. An example of this would be doing a set of HIITS, and anything up to about an 800 meter sprint. The Lactate system uses glucose to help create ATP. It breaks down the glucose molecule into pyruvic acid through anaerobic glycolysis (the splitting of sugars). Through this anaerobic glycolysis system chemical energy is released and used to synthesize two ATP molecules for every glucose molecule used. This is Zone 4.
3. The Aerobic System: this is the active system our body uses to sustain long duration low intensity efforts. Duration wise, think 5k, 10k and up. This system needs oxygen to be present for the creation of ATP and will use one of three processes to create it, Aerobic glycolysis, Krebs cycle or Electron transport chain (feel free to look those up if you are curious I’m not going to get that deep into the science). It's a slow process and thus is used for lower intensity demands but can continue for long periods of time. This is Zone 1, 2 and 3.
**Found this chart on a Google search, not my own. It gives a good visual of what I was talking about as far as how long each energy system lasts, and that there is some overlap between them.**
Physiological and Metabolic Adaptations of Zone 2 Training
Performing most of your training in Zone 2 will help you build endurance, durability and strength. In addition, these easy training sessions help you...
1. Increase the number and density of your mitochondria - as you know from reading earlier the mitochondria is where the muscle gets its energy to create muscle contractions.
2. Increased capillary pathways - means more oxygen carrying capacity, and more ability to keep going.
3. Increase Stroke volume - amount of blood pumped out of your heart per beat; more blood means more oxygen and longer duration exercise.
4. Increased Fat burning capability - your body can more easily access the fat and use it for energy.
5. Increased lactate clearance - the mitochondria has the ability to break down the lactate and reuse it.
6. Increased blood plasma - the liquid part of the blood that carries cells and proteins.
7. Allows you to increase your training volume without beating up your body.
How Do You Find You Zone 2
This is based on heart rate, and there are a couple ways to calculate it. If you do not have a heart rate monitor or prefer not to use one, using nasal breathing can help keep you in zone 2 in the beginning of your training. But, as you become more fit, your body will adapt and it really is helpful to use and track your heart rate. The best way to track heart rate is with the use of a chest strap.
One of the best ways to get started with heart rate training is to calculate your heart rate reserve (HRR). First start with gathering the following numbers:
1. Max Heart Rate: 220 - your age = MHR
2. Find your Resting Heart rate (RHR), this is taken immediately when you wake up, before sitting up.
3. Find your Heart Rate Reserve (HRR): Subtracting your Resting Heart Rate from your Max Heart Rate.
4. Multiply HRR by the Zone percentage you want to calculate, Zone 2 = 65-75% of MHR
5. Add back in your RHR to each of the calculated numbers in #4 to get your range for Zone 2.
For the other zones, the ranges are: Zone 3 multiply by 75-85%; Zone 4 multiply by 85-95%; Zone 5 multiply by 95-100%; Zone 5+ anything higher than Zone 5.
Here is an example: Let's say you are 40 years old, with a resting heart rate of 50 beats per minute.
MHR - RHR = HRR
(HRR x 65%) + RHR = Lower end Zone 2
(HRR x 75%) + RHR = Higher end Zone 2
220 - 40 = 180 MHR
180 - 50 = 130 HRR
130 x 65% = 84.5
130 x 75% = 97.5
88.4 + 50 = 138.4, Zone 2 low end
97.5 + 50 = 147.5, Zone 2 high end
According to this method this person's Zone 2 Heart Rate is 134 to 146 beats. This means in order for this person to train at a Zone 2 training threshold they would need to keep their heart rate in that range. Now this isn't the most accurate way to get your zones, but it's the best way for someone new to heart rate training, or just new to training in general. If you are interested in the more advanced method of attaining your actual Zone 2 threshold please feel free to ask me for help.
What About Zone 3?
You may have noticed I did not mention Zone 3 in the energy systems above. The reason is that Zone 3 is this grey area in performance training. Your body uses a mix of Lactate and Aerobic systems, with no specific ratio of either. So when you hang out in the Zone 3 "Grey Zone" your body isn't getting the best adaptations it can due to the mixing of the systems. In this zone you aren't going fast enough to improve speed or power, and you aren't going slow enough to improve the cardiovascular benefits mentioned earlier, plus the recovery time from Zone 3 comes at a high price.
When to Train the Zones
If you are training for an event, you’re going to want to start with building your base of fitness, Zone 2. This should be started as soon as you begin your training plan, and will last throughout your entire training up to your event. Let’s say you’ve got a 4 month training plan. You will want to get into some Zone 4 and 5 training intervals in that second month of training for short periods of time with significant recovery. Then in months 3 and 4 you’re going to start building up the number of intervals, or the length of time of the intervals in that zone 4-5 range. This is obviously just a basic starting point. A coach would be able to help you determine when these changes need to be made.
Wrap Up
Knowing what your heart rate training zones are will benefit you in many ways. It's not just for endurance athletes, but also those trying to keep a general health and fitness routine. So the next time you head out for your workout, make sure you know what the purpose of your training session is, and know what zone or zones you should be working out in.
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