VO2 max (also maximal oxygen consumption, maximal oxygen uptake, peak oxygen uptake or maximal aerobic capacity) is the maximum rate of oxygen consumption as measured during incremental exercise, most typically on a motorized treadmill. Maximal oxygen consumption reflects the aerobic physical fitness of the individual, and is an important determinant of their endurance capacity during prolonged, sub-maximal exercise. The name is derived from V – volume, O2 – oxygen, max – maximum.

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At 60-75% of maximum heart rate (HRmax), this non-straining intensity is used for recovery runs, warm-up, cool-down and long runs. The primary purpose is to build a base for more intense workouts by strengthening the heart and increasing the muscles' ability to use oxygen, and to recover between hard workouts. Daniels recommends that most training miles are performed in E pace.

At 76-88% HRmax, this intensity is aimed to raise the lactate threshold. The runner should be able to sustain this pace for up to 60 minutes during racing. Daniels describe this intensity as "comfortably hard". In elite runners, the pace matches the half marathon one, while less trained runners will run at around 10k pace. Daniels points out the importance of keeping the given pace to reap the benefits of the training.

Intensity at 89-100% HRmax. This intensity stresses the VO2max to raise the maximum oxygen uptake capacity. Since the pace is very intense, it can only be sustained for up to 12 minutes during racing. To cope with the intensity, and to train for longer periods of time, this training is performed as interval training, hence the name. The interval between each work bout should be a little less than the time of the work bout. Optimum intervals are 3–5 minutes long. There is no benefit to exceeding 5 minutes at this pace, under Daniels' theory, which means that despite the popularity of mile-repeats in many running groups, Daniels discourages them for people whose pace is slower than about 5:00/mile, preferring shorter intervals such as 1200 meters.