Why Sebastian Sawe's sub-two-hour marathon was so difficult

On April 26, 2026, Sebastian Sawe crossed the finish line at the London Marathon in 1 hour, 59 minutes and 30 seconds, becoming the first athlete to run a sub-two-hour marathon in an officially sanctioned race.

For decades, the two-hour mark had been regarded as one of the ultimate limits of human endurance. It was not just a sporting milestone, but a physiological boundary – one many researchers believed was nearly impossible to overcome under standard race conditions.

So why is breaking two hours so difficult – for a human?

An energy gap the body must overcome

At the most basic level, a marathon is a test of energy supply.

Running 42.195 kilometers at sub-two-hour pace requires roughly 2,500 kilocalories. Yet the human body's glycogen stores – the primary source of high-intensity energy, and it typically provide only about 2,000 kilocalories.

That leaves a metabolic gap of around 500 kilocalories.

To maintain speed, elite runners must increasingly rely on fat metabolism during the latter stages of the race. But fat is a slower-burning fuel. The challenge lies in sustaining near-maximum pace while shifting to a less efficient energy source without triggering a significant drop in speed.

Even small miscalculations in pacing or fueling can lead to rapid fatigue.

Running near the edge of oxygen capacity

Breaking the two-hour barrier also requires operating close to the body's aerobic limits.

Elite marathoners must sustain speeds near their maximal oxygen uptake for nearly two hours. This places them close to the threshold where the body begins to accumulate fatigue-inducing byproducts.

At this intensity, the margin for error is extremely small.

A slightly higher pace risks early exhaustion, while a slightly lower pace makes it impossible to achieve the target time. Maintaining that balance requires not only exceptional cardiovascular capacity, but also precise pacing strategies and environmental conditions.

Precision repeated thousands of times

Beyond metabolism and oxygen, biomechanics play a crucial role.

To maintain sub-two-hour pace, elite runners typically sustain a cadence of 180 to 190 steps per minute, with ground contact times below 200 milliseconds. Over the course of a marathon, that translates into tens of thousands of steps executed with near-perfect consistency.

Any small inefficiency in stride length, posture, or foot strike could increases energy expenditure. Over time, these minor deviations accumulate, reducing overall performance.

In this sense, a sub-two-hour marathon is not just a test of endurance, but of mechanical precision sustained over long distances.