{"id":38721,"date":"2026-03-23T08:00:00","date_gmt":"2026-03-23T08:00:00","guid":{"rendered":"https:\/\/whatracetorun.com\/how-to-avoid-hitting-the-wall-marathon\/"},"modified":"2026-03-23T08:00:00","modified_gmt":"2026-03-23T08:00:00","slug":"how-to-avoid-hitting-the-wall-marathon","status":"publish","type":"post","link":"https:\/\/whatracetorun.com\/?p=38721","title":{"rendered":"How to Avoid Hitting the Wall in a Marathon: Fueling, Pacing, and Training Tactics"},"content":{"rendered":"

Mile 20. Everything was going perfectly \u2014 your splits were dialed in, your legs felt strong, your confidence was sky high. Then, without warning, the wheels came off. Your pace slowed to a shuffle, your legs turned to concrete, and those final 6.2 miles felt longer than the first 20 combined. You hit the wall. Hitting the wall marathon<\/em> runners call it “bonking,” physiologists call it glycogen depletion, and just about every runner who has experienced it calls it their worst running memory. The good news: it is almost entirely preventable with the right combination of fueling, pacing, and training. This guide explains exactly how.<\/p>\n

The Physiology of Hitting the Wall: Why It Happens<\/h3>\n

Your muscles run primarily on two fuels during a marathon: glycogen (carbohydrate stored in your muscles and liver) and fat. At easy, conversational paces, your body burns a comfortable mix of both \u2014 fat provides the majority of energy and glycogen is spared. But as race pace climbs toward marathon effort, your body shifts increasingly toward glycogen because it can be burned faster than fat to meet the energy demand. The problem? Your total glycogen stores \u2014 roughly 400\u2013500 grams, equating to about 1,600\u20132,000 calories \u2014 are finite. Burn through them and your body is forced to slow down dramatically, often abruptly, to match a pace it can sustain on fat alone. That sudden deceleration is the wall.<\/p>\n

Research published by the American College of Sports Medicine (ACSM)<\/a> shows that trained marathon runners can deplete liver glycogen within 90\u2013120 minutes of sustained effort at race pace without exogenous carbohydrate intake. At a 4-hour marathon pace, that’s roughly mile 16\u201318 \u2014 precisely where most runners report hitting the wall. Fortunately, fueling during the race can dramatically extend your glycogen runway.<\/p>\n

Fueling Math: How Many Carbohydrates You Actually Need<\/h3>\n

The science here is more precise than many runners realize. Current sports nutrition consensus recommends consuming 60\u201390 grams of carbohydrates per hour<\/strong> during efforts lasting longer than 75\u201390 minutes. At the lower end (60g\/hr), your gut can absorb glucose alone. At the upper end (up to 90g\/hr), you need a combination of glucose and fructose, which use different intestinal transporters \u2014 this is why many modern gels and sports drinks blend maltodextrin with fructose.<\/p>\n

For a 4-hour marathon, that means consuming roughly 240\u2013360 grams of total carbohydrate during the race \u2014 a target most runners fall dramatically short of. A single gel typically delivers 22\u201327 grams of carbohydrate. To hit 60g\/hr, you need roughly one gel every 30\u201335 minutes plus<\/em> some additional carbohydrate from sports drink or chews. To approach 90g\/hr, you need to consistently take in gels or chews alongside carbohydrate-containing drinks at every aid station.<\/p>\n

Here’s a simple fueling framework to build around:<\/p>\n