Holmer says the 80/20 rule is an artifact of high mileage
If you only have a few hours a week, Holmer says more of them should be hard.
Brady Holmer says the 80/20 rule, the idea that roughly 80 percent of training should be easy, is mostly a byproduct of running a lot, not a rule to follow.
In a post on X he puts it plainly. When you train enough hours, most of that work has to be low intensity by necessity, because nobody can absorb that much hard running. The 80/20 split is what falls out of a big weekly volume, not the reason the volume works. His conclusion for everyone else is that time-limited exercisers are better off putting more of their training at higher intensities.
The “80/20” rule is (mostly) an artifact of athletes with high training volumes… not a prescription.
The paradox nobody has solved
Holmer's starting point is the thing that should bother more runners. Easy running barely challenges a well-trained athlete's heart and lungs, so on paper it should not make them fitter, and yet elites do enormous amounts of it.
He points to a 2025 perspective paper that calls this a paradox and offers seven possible explanations, none of them proven. Among them, that easy sessions give fitness without the stress, since heart rate recovery after a hard session can take over two days while recovery from an easy session happens in under 24 hours, which caps most athletes at two or three well-rested hard sessions a week. Others on the list include years of structural change such as a bigger heart, more capillaries and more slow-twitch fibers, something not yet measured such as durability, and the mental side, since easy exercise tends to lift mood while a block of hard training increases distress.
The last explanation is the one that cuts against the orthodoxy. Holmer writes that easy work may be replaceable, that intensified training could work, but that it raises concerns about overtraining and injury and that studies show no clear performance advantage.
What it actually means
This is not an argument that easy running is useless, and Holmer said so directly when pushed in the replies. If you are out there for hours on end, he says, that is exactly where zone 2 becomes beneficial. His quarrel is with the claim that low intensity is somehow superior for driving adaptations like VO2 max, which he calls incorrect.
The whole thing, in his words, comes down to a trade. Less time available means going harder more often. That is a very different message for a 40 mile a week marathoner than it is for a 120 mile a week pro, which is roughly the point several coaches have been making in the wider zone 2 fight.
A 2025 perspective paper calls this a paradox and proposes 7 possible explanations. None are proven.
this whole discussion is basically “if you devote less time to exercise, go harder more often.
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