Consistency is counterfactual

Endurance sport is the most interesting laboratory for human performance because it allows for objective measurement and has enough competition to understand what counts as impressive. For example, we know that running a marathon in two hours is a major achievement because many people have attempted to do so under similar conditions.

It is therefore striking that there is a universal agreement among athletes and coaches about the most important condition for success in endurance sports: consistency of training. This is something you hear over and over again when athletes and their coaches are asked about the secrets underlying this or that impressive performance.

While there’s universal agreement that consistency is the most important factor for performance, I’ve never seen a definition for the concept. It’s got that notorious “you know it when you see it” quality. What I imagine people mean when they talk about consistency in endurance training is some kind of smooth graph of weekly mileage or time in the weeks and months leading to an event.

But the smoothness of the graph isn’t a sufficient condition for “consistency”. Here is a training plan that’s easy to follow consistently but is unlikely to land you on the podium in your next local marathon: run 3 kilometres every week. Following this plan will produce a smooth graph of consistent mileage, but it will not deliver the stimulus needed to produce the adaptations that will make you fast.

Here’s another training plan that will also not land you on the podium: run 300 kilometres each week. This plan will get you injured pretty quickly, leading to weeks of missed training and risking a DNS at that local marathon.

Still, if you asked professional runners whether they would rather follow the 3K or the 300K plan, I’m willing to bet that a surprising proportion of them would opt for the 300K option. This is because professional endurance athletes are almost invariably predisposed to do too much rather than too little. It is probably pretty hard to put in the thousands of hours of monotonous training required to become a professional endurance athlete unless you have this kind of predisposition.

And that’s the key to the definition of “consistency”. Because the context of the discussion is professional endurance sports, the assumption is that athletes are always on the verge of doing too much, risking injury. When it is a given that everyone is doing as much as they possibly can, the idea of consistency becomes about moderating your load so as to avoid prolonged pauses in training due to injury or lack of recovery.

From this perspective, consistency becomes a counterfactual concept. To be “consistent” in endurance training is to sustain a load such that:

• if you trained less, you would miss out on some adaptations
• if you trained more, you would get injured

The above definition ignores some other important considerations such as rest, recovery, nutrition, etc. When these variables are included in the definition, selecting the best training intervention becomes a counterfactual multi-objective optimization problem. When athletes and their coaches manage to solve this problem successfully, it gets called “consistency”.