What the 80/20 distribution actually means
Polarized training describes how elite endurance athletes distribute intensity: roughly 80 percent of training sessions sit in the easy, low-intensity zone below the first lactate threshold, and around 20 percent are genuinely hard, above the second threshold. Comparatively little time is spent in the moderate threshold zone in the middle.
The percentages are usually counted by sessions or time, and exact splits vary by sport and phase. The defining feature is the avoidance of the 'gray zone,' where effort is too hard to recover from easily but too easy to drive top-end adaptation.
Why the middle gets skipped
The logic is that large volumes of easy work build aerobic base and allow recovery, while a smaller dose of high-intensity work stimulates VO2max and threshold gains. Spending too much time in the middle is thought to accumulate fatigue without proportional benefit.
Evidence supports polarized distributions for well-trained endurance athletes, but threshold-heavy models also produce gains, and the best distribution depends on the individual and training phase. This is general educational information about training theory, not personalized coaching or medical advice.