GLOSSARY

During-Exercise Nutrition provides food and fluid during activity when useful for its duration, intensity and conditions. Short and long sessions need different plans.

Carbohydrate requirements vary with the intensity, duration and importance of the work. Daily intake relative to body mass describes a different quantity from an intake rate during exercise, which is commonly expressed per hour. A larger daily target does not mean the same amount should be consumed in every session. Match supply to the schedule, starting stores and practical tolerance, and distinguish grams eaten from grams absorbed or oxidized when discussing a fueling plan.

Muscle and liver glycogen have related but different roles. Muscle glycogen supplies the muscle in which it is stored, while liver glycogen helps support blood glucose. An overnight fast can reduce liver carbohydrate availability without producing the same depletion in every muscle. Starting concentration, recruited fibers and exercise demand affect use. An estimate of total stores does not directly describe the availability of every local glycogen pool during a specific movement.

Exogenous carbohydrate comes from food or drink, while endogenous carbohydrate comes from existing body stores. Digestion, intestinal absorption, circulation, muscle uptake and oxidation are separate steps. Tracer studies can estimate oxidation of ingested substrate under defined assumptions. The amount consumed is not the amount oxidized immediately, and a high measured oxidation rate does not alone prove better race performance. Specify the substrate source and the process measured before comparing research or planning intake.

Glucose and galactose use intestinal SGLT1 transport, while fructose uses GLUT5. Combining suitable carbohydrate sources can engage different absorption pathways and increase exogenous carbohydrate availability under relevant conditions. Maltodextrin yields glucose units during digestion rather than creating a separate fructose transport pathway. The blend, total intake, fluid provision, exercise and tolerance all matter. No single glucose-to-fructose ratio or hourly intake is a universally optimal prescription for every athlete and event.

Gut training means practicing the intended food and fluid strategy during suitable training sessions and progressing according to tolerance. Repeated exposure may improve comfort or handling, but symptom improvement does not directly prove increased transporter expression in an individual. Glucose and fructose transport involve different proteins and their adaptation is a specific research question. Record actual intake, conditions and symptoms. A very high intake used successfully by one athlete should not be treated as the starting requirement for everyone.

Periodization adjusts nutrition across sessions, days or training phases to support the work and its goals. Carbohydrate can be concentrated around demanding or important sessions while the broader diet still meets energy and nutrient needs. A lower-demand day can also be a recovery or preparation day, so rest does not imply that food or carbohydrate should be removed. Describe what changes, when and why, and evaluate the quality of subsequent training rather than treating variation itself as beneficial.