You rested for two days during Phase One, but now we're upping the ante. It's time for a cardiac power workout. At the tissue level, training cardiac power will increase the strength and contractile abilities of your heart muscles, which will further improve oxygen delivery. Training this system will also improve your body's utilization of oxygen to produce energy within the working muscles. In other words, you'll improve your ability to use the aerobic energy system at higher rates of exertion.
Today's workout is similar to what you did on day 16, but the work and rest intervals are longer. This time, I want you to sustain a high level of work for 2 minutes. Choose a rate at which you don't have to stop to rest. After the work period, you'll have 4 minutes to recover. Repeat this 5 more times for a total of 6 sets.
Keep water handy as you go through this workout. Hydration will help you perform better.