Zone 4 workouts are typical training sessions around your (lactate) anaerobic threshold. These are intense (interval) workouts, usually with longer intervals, where the body must learn to cope with the rapid acidosis that occurs due to the high intensities.
At zone 4 intensities, the body is no longer able to buffer and/or break down the accumulated waste products adequately. These waste products quickly build up in the muscles and blood, negatively affecting your performance. As the contribution of the anaerobic system increases, the body primarily uses carbohydrates to supply the necessary energy. These carbohydrates are mainly broken down into lactate, which can then be processed by the aerobic system to generate energy.
Energy System
All training sessions at Science2Move are structered using personalized training zones. These zones are determined through a maximal ramp test, during which changes in energy systems are analyzed. During a maximal ramp test, we determine your zone 4 based on:
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the anaerobic threshold
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the second steep increase in your breathing frequency and volume of air you inhale per minute
To rapidly release the energy needed for the higher pace in zone 4, the body must break down nutrients faster. Since the aerobic system can no longer release energy at the required rate, the anaerobic system steps in more and more. The higher the intensity in zone 4, the greater the contribution from the anaerobic system. Due to the high energy demand in a short period of time, the phosphate system will also play an increasingly larger role at higher intensities. However, this increased rate also leads to the production of more waste products. This results in acidosis and, eventually, a steep increase in your breathing rate and the amount of air you inhale per minute. We can observe this in the test data through your accelerated breathing and the ratio between CO₂ output and oxygen intake. The greater the contribution from the anaerobic and phosphate systems, the more waste products will be produced. Ultimately, this leads to a second increase in your breathing rate (the second steep increase in your breathing frequency).
When you have downloaded a training program from Science2Move on TrainingPeaks, we will use general training zones, based on FTP and the principles of zone 1. The exercise intensity will approximately be in the range of:
- Bike power: 100-104% FTP
- Bike HR: 100-102% FTHR
- Run pace: 100-103% FTPa
- Run HR: 100-102% FTHR
What Are You Training?
Training in zone 4 stimulates your body to cope with the buildup of waste products and to (quickly) remove/buffer these by-products and acidosis. You also encourage your muscles to use the lactate produced as an energy source. Additionally, zone 4 workouts, due to their high intensities, are excellent for training coordination, speed, and strength.
Zone 4 training is a great (and perhaps even essential) addition to your training program!
Nutrition & Hydration
If you spend a lot of time cycling or running in zone 4, nutrition becomes very important. You are using a lot of carbohydrates. Carbohydrates are stored in limited amounts in your body—mainly in your muscles and liver. Once these reserves are depleted, you will no longer be able to even cycle or run in zone 3. This is known as “hitting the wall” or “bonking”. Since your brain also relies on carbohydrates, it’s essential to keep replenishing them. Also, make sure to drink enough fluids, as you will lose a lot of fluid, especially in hot weather or strong winds!
