For as long as marathoners have traded war stories, hitting the wall has been explained with a single word: glycogen. Run out of carbohydrate somewhere around 30 kilometres, the story goes, and the body simply downshifts. A review published this month argues that explanation is incomplete to the point of being misleading. Synthesising evidence across physiology and psychology, the authors propose that late-race collapse is better understood as a failure of durability — the capacity to resist deterioration over time — with fuel just one of many systems that can give way.
The review catalogues an intimidating list of contributors: metabolic stress, thermoregulatory strain, dehydration, gastrointestinal dysfunction, neuromuscular fatigue, biomechanical deterioration, shifting perception of effort and plain pacing error. Crucially, these mechanisms interact rather than act alone. A hot day increases sweat loss, which stresses the gut, which limits fuelling, which accelerates glycogen depletion, which degrades running form, which raises the energy cost of every remaining kilometre. The wall, in this framing, is less a cliff edge than a cascade.
The paper lands in the middle of a broader shift in endurance research. Beyond the three classical pillars of marathon performance — maximal oxygen uptake, lactate threshold and running economy — physiologists have increasingly focused on durability, sometimes called fatigue resistance: how well those numbers hold up in the final third of a race. Studies of elite performances suggest the best marathoners are distinguished less by their fresh physiology than by how little of it they lose after two hours of running, an insight big-data analyses of race performances, including work published this month in the Journal of Applied Physiology, are beginning to quantify at scale.
The practical implications will look familiar to well-coached athletes, but the framework explains why they work. Long runs that finish with quality teach the body to hold form and output on tired legs. Strength training buys resistance to the muscle damage that erodes economy late in races. Practised in-race fuelling defends the gut as well as the glycogen stores. And realistic pacing is recast not as caution but as durability management: every minute spent above sustainable effort early is borrowed, with interest, from the final 10K.
None of this makes the wall mythical — runners will go on meeting it every autumn marathon weekend. But the reframing matters. If late-race collapse has eight causes rather than one, then gels alone were never going to be the whole answer, and training that targets durability directly becomes the most rational insurance a marathoner can buy. With Berlin, Chicago and New York all approaching, the timing of the reminder is apt.