What’s the Toughest Part of a Marathon? Unpacking the Wall, Fatigue & More

When you line up for a marathon is a 42.195‑km (26.2‑mile) road race that pushes your body and mind to the limit, the question on most runners' minds is: what is the toughest part of a marathon?

Why the Mid‑Race Energy Crisis feels like the hardest stretch

About the halfway point, many runners hit what the community calls the wall is a a sudden drop in energy caused by depleted glycogen stores, typically around 30-35 km. Your liver and muscles have been burning stored glucose for hours; once those reserves run low, the body flips to burning fat, which is slower and feels exhausting.

Data from a 2023 study of 5,000 marathon finishers showed that 68% reported feeling a noticeable slowdown between the 30‑km and 35‑km marks, and their average pace dropped by 12% compared to the first half.

• Glycogen depletion is the main trigger.
• Symptoms include heavy legs, mental fog, and an urge to stop.
• Recovery without proper fueling can turn a slow finish into a DNF.

Hydration and electrolytes - the silent performance killers

Even a small 2% loss in body water can sap power. Hydration is the process of replacing fluids lost through sweat, while electrolyte balance keeps muscles firing correctly.

Runners who skip water stations or drink only plain water often develop cramping because sodium levels fall. A 2022 field survey of the Berlin Marathon found that participants who consumed a sports drink with 300mg of sodium per liter had 22% fewer cramps than those who only drank water.

1. Start the race with a urine color lighter than lemonade.
2. Aim for 400-800ml of fluid per hour, adjusting for temperature.
3. Include a sports drink or salty snack every 45minutes.

Muscle fatigue and form breakdown

As the race progresses, muscle fatigue is a the decline in the ability of muscle fibers to generate force, often accompanied by altered running mechanics. The quadriceps and calves bear the brunt, leading to over‑striding and heel‑striking that waste energy.

Research from the University of Colorado (2021) showed a 15% increase in ground‑contact time after 30km, directly linked to slower speeds. Small changes-like shortening your stride by 5%-can cut that time back and keep you moving efficiently.

• Incorporate downhill running in training to strengthen eccentric control.
• Practice cadence drills (180 steps per minute) once a week.
• Use compression sleeves if you struggle with calf tightness.

Heat, humidity, and environmental stress

Running 42km in 20°C (68°F) feels very different from the same distance in 30°C (86°F). Heat stress is a condition where core body temperature rises above safe limits, impairing performance and increasing risk of illness accelerates glycogen depletion and raises perceived effort.

During the 2024 Chicago Marathon, runners who wore light, moisture‑wicking fabrics finished on average 6% faster than those in heavier gear, according to race‑track timing data.

1. Choose breathable clothing and a hat.
2. Slow your early pace by 5-10% on hot days.
3. Take advantage of any shaded sections for brief breathing breaks.

Mental fatigue - the invisible barrier

After hours of pounding the pavement, the brain starts to flag danger. Mental fatigue is a a state of reduced cognitive performance and motivation, often triggered by prolonged physical exertion makes every kilometer feel longer.

Elite runners use visualization, mantra repetition, and segment goals to stay focused. A 2020 interview with an Olympic marathoner revealed that breaking the race into five 8‑km “mini‑races” helped maintain a positive mindset even when the body screamed to quit.

• Pick a personal mantra (“Strong, steady, forward”).
• Set micro‑targets (next water station, next hill).
• Practice mental drills in long runs (e.g., “run the next mile with a smile”).

How to tackle the toughest segment effectively

Putting the pieces together, the part most runners label as the hardest is a combination of glycogen depletion, dehydration, and mental wear‑out that usually strikes between 30 and 35km. Here’s a practical game plan:

1. Fuel early and often: Consume 30-60g of carbs per hour from the start using gels, chews, or sports drinks.
2. Maintain steady hydration with electrolytes - aim for a sodium intake of 300-600mg per hour.
3. Adopt a slightly slower pace before reaching 30km to spare glycogen.
4. Practice “cognitive pacing” - repeat your mantra and glance at your watch only at designated checkpoints.
5. Include a short, easy walk for 30 seconds at the 30‑km aid station if you feel the wall looming; it clears lactate and resets breathing.

When you train with these habits, the dreaded wall becomes just another mile you’ve prepared for, not an unexpected barrier.