Gels shouldn't be a rescue solution

By 

Giles Elmore (BSc Hons) MRSPH

Why we need to preserve glycogen rather than replace it 

When speaking with a new client about performance or endurance nutrition the first two questions I’m usually asked are about “What should I take?” and “How much should I take?”, Perhaps the first question should be ‘When should I take..’? Because when it comes to carbohydrate availability and performance, timing may matter far more than most cyclists realise. Here’s why… 

One of the biggest misconceptions in endurance nutrition is the idea that taking a gel midway through a ride simply refills glycogen. In reality, by the time slight hints of fatigue begins to appear and the first energy gel is taken, glycogen levels have often been falling steadily for a good amount of time. And once muscle glycogen becomes significantly depleted, performance may not fully recover, even when carbohydrates are consumed. That distinction matters because it completely changes how fuelling should be approached. Fuelling during exercise should not be a rescue or reactive, it should be treated as preservation. 

To understand why, we first need to understand what glycogen is. Carbohydrate is stored within the muscles and liver in the form of glycogen. These stores are relatively limited, typically around 400 to 600 grams depending on muscle mass, training status, and nutritional intake. During moderate to high intensity riding, however, carbohydrate usage can be remarkably high. Research has shown cyclists can oxidise carbohydrates at rates exceeding 80 to 100 grams per hour depending on intensity and training status. A rider not pushing hard for a few hours can burn through a substantial proportion of glycogen stores surprisingly quickly, particularly if fuelling is delayed or inconsistent. And while gels and sports drinks absolutely improve performance, they are not instantly replacing glycogen stores inside the muscle. Instead, they are acting as a secondary fuel source. 

This process is known as exogenous carbohydrate oxidation, essentially burning carbohydrate consumed during exercise rather than stored glycogen. In practical terms, the gel consumed during the ride becomes readily available fuel in real time, helping reduce the rate at which remaining glycogen is being depleted. This is where timing becomes critical. Taking carbohydrates early in a ride helps preserve glycogen before levels become low. Waiting until the legs already feel empty means trying to support a system that is already under strain. 

Most cyclists treat fuelling as an emergency response, however, physiologically, it works far better as prevention. 

This is one reason modern endurance nutrition recommendations have shifted so dramatically over recent years. Riders are now encouraged to fuel earlier and more consistently, rather than waiting for hunger or fatigue to appear. Because by the time you feel under fuelled, carbohydrate availability has often been dropping for a considerable period of time already. 

Recent research examining exercise under low glycogen conditions helps explain why this matters. A 2025 study by Martin Thomassen et al. investigating performance with depleted muscle glycogen demonstrated significant reductions in high-intensity exercise capacity despite fuel still being available elsewhere within the body. Participants operating with low muscle glycogen showed markedly impaired performance and earlier fatigue, even when carbohydrates were still being consumed. 

Why? 

Because muscle glycogen appears to do more than simply act as stored fuel. Unlike carbohydrate circulating within the bloodstream, glycogen exists locally within the muscle itself, immediately available for rapid energy production. Research increasingly suggests glycogen availability also influences muscular function directly, including processes involved in muscle contraction itself. In simple terms, once muscle glycogen becomes critically low, the issue is no longer just “energy.” The muscle itself begins functioning differently. 

This helps explain something almost every cyclist has experienced. Even after finally taking a gel late into a hard ride, the legs rarely feel completely restored. The rider may still be able to pedal, but the sharpness has gone. Repeated accelerations become difficult. Climbs feel harder than they should. The ability to lift the pace fades. The fuel is arriving, but it is arriving too late to fully recreate the physiological advantages of well-stocked muscle glycogen.