Most athletes consuming carbohydrate during one-hour training sessions are wasting their money and their gels. The evidence for intraworkout carbohydrate is frequently misapplied — lifted from ultra-endurance or marathon research and transplanted onto training contexts where the physiology doesn't support it. There is a duration threshold below which intraworkout carbohydrate has no measurable performance benefit and one clear inflection point above which the evidence is compelling.
That threshold is approximately 75 minutes. Below it, muscle glycogen depletion during moderate-to-high intensity exercise does not progress far enough to impair performance acutely, and blood glucose remains stable through hepatic glycogenolysis. Above 75 minutes, glycogen depletion rate — which is non-linear and accelerates as stores deplete — begins to intersect with the sustained demand of the session, and exogenous carbohydrate becomes genuinely performance-preserving.
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Jeukendrup et al. (2004) systematically characterised the dose-response relationship across multiple durations and intensities. The landmark observation was that at 60 minutes of high-intensity cycling, carbohydrate versus placebo produced no significant time trial performance difference — the glycogen stores were not yet limiting. Extending duration to 90 minutes produced clear, significant benefits. The mechanism: during the first 45–60 minutes, even at high intensities, a well-fed athlete's muscle glycogen remains in a range that does not limit power output; it is the sustained depletion into the second hour that crosses the performance floor.
However, an important exception exists: the oral carbohydrate rinse effect. Rollo et al. (2010) in the *International Journal of Sports Physiology and Performance* demonstrated that swilling (not swallowing) a carbohydrate solution produced a 1% performance improvement even in well-fed 1-hour trials. The mechanism operates through opioid and reward receptors in the oral mucosa signalling to the motor cortex — a cephalic phase response that reduces perceived effort without substrate delivery. This effect is brief and dose-insensitive, but provides a low-GI-disruption strategy for shorter efforts.
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For sessions exceeding 75 minutes, the dose targets are well-established. At 30–45g carbohydrate per hour, performance is meaningfully supported without gastric stress. At 60g/hour, glucose transport capacity (SGLT1) begins to approach saturation, making this the ceiling for single-transporter (glucose/maltodextrin only) carbohydrate. Extending to 90g/hour requires a dual-transporter formulation (2:1 glucose:fructose), leveraging parallel GLUT5 fructose absorption — otherwise fructose ferments colically and produces GI distress.
The blood glucose floor matters more than most athletes appreciate. Performance degradation begins when blood glucose drops toward 3.5–4.0 mmol/L — a level that can be reached within 90–120 minutes of sustained moderate-to-hard intensity without exogenous carbohydrate. The endpoint is not only glycogen depletion but hypoglycaemia-driven central governor activation, which reduces power output as a protective metabolic brake regardless of peripheral glycogen status. Gel timing should therefore be pre-emptive, not reactive — the first intake at 20–30 minutes prevents the curve from reaching this floor rather than rescuing performance after the fact.
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For training purposes versus racing purposes, the calculus differs. In training, strategic sessions performed with low carbohydrate availability (fasted or low-carb) produce superior mitochondrial adaptation through AMPK and PGC-1α activation. But when a session's goal is quality output — race-pace intervals, key threshold work — full carbohydrate availability preserves the power output needed to achieve the intended training stimulus. The tool is not one-size-fits-all; it is periodised according to the session's objective.
Calculating how many gels your specific race or long ride requires — based on duration, intensity zone, and your body weight — removes the guesswork from intraworkout fuelling. The calculator at winsport.uk/tools/nutrition/energy-gel-calculator estimates the number of gels per hour and total session requirements based on your duration, pace, and body weight, giving you a starting protocol that can be refined through gut training.
Do you carbohydrate-fuel all training sessions, or do you periodise your fuelling based on the session type and duration?