GLOSSARY

Running Economy describes oxygen or energy cost at a specified running speed under stated conditions. Surface, technique, fatigue and substrate use can influence the result.

Exercise economy describes oxygen or energy cost at a specified task output, while mechanical efficiency relates external work to metabolic energy input under a stated convention. Gross, net and other efficiency definitions differ in how baseline costs are handled. A lower oxygen cost is not automatically the same as higher maximal aerobic capacity. Compare the same workload, conditions and calculation method, and distinguish a measured physiological change from a demonstrated improvement in race performance.

Exercise uses a mixture of fuels whose proportions change with intensity, duration, training and diet. The crossover concept describes a shift toward greater carbohydrate contribution as intensity rises under specified conditions. It is a model of relative fuel use, not an on-off switch that turns fat metabolism off. The crossover point is not fixed across all individuals or protocols. Interpret substrate patterns with the actual workload and available fuel rather than a universal heart-rate zone.

A sustained low-carbohydrate, high-fat diet can increase reliance on fat and change fuel handling. Nutritional ketosis is a related but more specific state and is not produced by every higher-fat diet. Increased fat oxidation does not establish better performance, particularly when high rates of carbohydrate-supported work are required. Some athlete studies have found impaired exercise economy or high-intensity performance. Restoring carbohydrate after fat adaptation does not guarantee immediate reversal of every effect or the advantages of both approaches.

For example, compare oxygen cost at the same running speed or energy input at the same cycling power. A lower cost and a higher maximal capacity describe different adaptations. Consistent conditions help determine whether a measured change is real and whether it transfers to the athlete's actual event performance.

External training load describes the work performed, such as distance, power or repetitions. Internal load describes the athlete's response, such as heart rate or perceived exertion. Volume, intensity and duration contribute differently, so one summary number does not reveal all nutritional demands. Two sessions with similar duration can differ greatly in carbohydrate use and recovery needs. Food planning should reflect the actual work and subsequent schedule, while persistent mismatch between intake and load deserves review.

Total expenditure includes energy needed at rest, the thermic effect of food and physical activity. Planned exercise is only part of activity expenditure. Work, walking and spontaneous movement can also matter. When an estimate already includes a component, adding it again double counts energy. Establish whether an exercise value is gross or net of resting expenditure, and use the same convention when comparing days or combining wearable estimates with a daily energy model.

A nutritional strategy should be evaluated by the quality and relevance of evidence, the athlete's response and the feasibility of implementation. Molecular signaling, a substrate-oxidation change, a laboratory capacity test and race performance are different outcomes. Association does not establish cause, and a response in one small study need not generalize to all athletes. Define the intended benefit before changing the plan, then evaluate training quality, recovery and performance under comparable circumstances rather than judging success by novelty.