The science of long-distance running

As marathon times fall, the debate over footwear, diet, and performance continues

It was only a matter of time… and what a time it was. On 26 April, at the London Marathon, Kenya’s Sabastian Sawe achieved a world record and broke the two-hour barrier, finishing in 1:59:30, with Ethiopia’s Yomif Kejelcha clocking 1:59:41 for second.

Had this been anticipated? Joyner et al, writing in the Journal of Applied Physiology (2011; 110: 275), suggested that based on recorded times from 1960, it will take 12–13 years to break two hours, “assuming a 20-second reduction per year”. Their estimate was two years out, unlike Alex Hutchinson, recalling in his Endure (2018) that in 2014, when Runner’s World magazine asked him to consider the physiological, psychological, and environmental determinants of a sub-two-hour marathon, “the barrier would fall, I wrote, in 2075.” However, while co-founder of www.LetsRun.com Robert Johnson admits writing in 2013 that “I wasn’t sure we would see one in my lifetime,” he proffers the excuse that he “didn’t anticipate super-marathon shoes featuring super foams and carbon plates. The truth is, if we had 2013 shoe technology, we’d be nowhere near a sub-two-hour marathon.” This, it seems to me, is Johnson attempting to turn a fall into a dive.

Sawe wore Adidas lightweight, carbon-plated Adizero shoes. So what? All sport is helped by technology, but a telling insight comes from Ed Caesar’s Two Hours (2015). When Adidas presented to Kenyan marathoner Geoffrey Mutai a pair of running shoes containing an innovative boost foam, Caesar notes that “the athlete’s first question was not whether it would allow him to race faster, but whether it would allow him to train harder”. It’s the quality of one’s training that’s an important determinant of success. However, down at the opposite end of the running spectrum, I’m convinced that a regular training regime, combined with intermittent use of my Nike Elite racing shoes in the run-up to the 1981 London Marathon, helped me to a sub-three-hour time. Yes, it was mainly the training, but had I worn my everyday trainers for the race, my running style would have had the comparative fluency of a lead-booted diver. So, does Sawe’s use of light, cushioned shoes amount to “mechanical doping”, as some might insinuate? No.

Another aspect of Sawe’s magnificent achievement that many have remarked on is his apparently prodigious carbohydrate ingestion at a rate of 115g/h over the course of the race. The scientific analysis of carbohydrates in endurance sport during the modern era derives from the work of Swedish exercise physiologist Bengt Saltin (1935–2014), as reported by Bergström et al in Acta Physiologica Scandinavica (1967;71: 140–150), and from which the concept of carbohydrate loading evolved. But as with many aspects of medicine – the aetiology of stomach ulcers; the role of cholesterol in heart disease – the science is not always settled. For example, Prins et al in Am J Physiol Cell Physiol (2025;328: C710–C727) tested the widespread view that very-low-carbohydrate high-fat diets (LCHF) impair prolonged exercise performance. They compared LCHF with high-carbohydrate diets in competitive triathletes, finding that after a six-week diet adaptation, time-to-exhaustion (TTE) performance was similar for both diets. Light carbohydrate intake (10g/h) during exercise eliminated exercise-induced hypoglycaemia and improved TTE by 22 per cent on both diets: “These findings suggest that LCHF diets do not impair exercise performance and require a four-week adaptation period for metabolic homeostasis.” Studies like this contribute to a paradigm shift in sports medicine thinking, which might have prompted the editors of Am J Physiol Cell Physiol to cite Prins et al’s article as the Best Impact Paper of 2025.

However, the question of maintaining insulin sensitivity while ingesting high-carbohydrate diets hangs over us all, including elite athletes. For example, on the last page of his autobiography The Stubborn Scotsman (2016), Don Ritchie MBE (1944–2018), widely regarded as the 20th Century’s finest ultra-distance runner, and who consumed a consistent  high-carbohydrate diet, observes: “My decades of running have not protected me from some serious health issues of which [type 2] diabetes is the most significant long-term condition. Diabetes may have contributed to plaque deposits in my arteries, which led to angioplasty in 2008.”

Exercise is important, but the enjoyment of running is not dependent on the nutritional mayhem of a daily ‘carbathon’. Beware the siren calls of the sports drink and gel marketeers in glossy running magazines and reflect on the fact that one can’t outrun a bad diet.