GLOSSARY

Harris–Benedict Equation refers to a family of equations estimating basal or resting expenditure from body characteristics. Original and revised Harris-Benedict versions use different coefficients, so the exact version must be named.

Prediction equations link measured characteristics such as mass, height, age or fat-free mass to an expected resting expenditure in a reference population. Versions and required units differ, and an equation's output is not a direct metabolic test. An athlete can differ from the development sample. State the equation version and inputs, and reassess its usefulness against appropriate measurements and real-world trends. A discrepancy should prompt evaluation of both prediction and measurement conditions rather than an automatic diagnosis of metabolic damage.

Basal measurements require stricter conditions than many resting measurements, including a postabsorptive state, physical rest and a thermoneutral environment. Resting energy expenditure and basal metabolic rate are closely related but not automatically interchangeable. Recent training, food, stimulants, illness and measurement procedures can affect results. A prediction equation supplies an estimate for a population and its inputs, whereas properly performed indirect calorimetry measures respiratory exchange under the conditions of that particular test.

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.

Validity concerns whether a method estimates the intended quantity accurately, while reliability concerns consistency on repetition. A method can repeat well while remaining biased. Technical error and prediction error also describe different sources of uncertainty. Small changes should be interpreted relative to relevant measurement error, with the same protocol used over time. Agreement at group level does not guarantee close agreement for every individual athlete, and switching instruments can create an apparent change that is methodological rather than biological.

Energy requirements depend on body size and composition, activity, life stage and physiological circumstances. A maintenance estimate is a starting point for a defined situation rather than a permanent personal calorie ceiling. Training load, recovery, appetite and changes in body mass help evaluate its usefulness. Growth, illness or a change in training schedule may require reassessment. Adequate energy also needs appropriate carbohydrate, protein, fat and micronutrient provision; matching a calorie total alone does not guarantee a balanced sports diet.

Energy expenditure can change during weight loss because a smaller body costs less to maintain and move, and because additional adaptive responses may occur. These explanations should be distinguished rather than calling every reduction a damaged metabolism. Appetite and spontaneous movement can also change. The size and persistence of adaptation vary. Reassess trends and recovery under comparable conditions instead of assuming that an equation's initial prediction remains the correct maintenance intake throughout a changing training and weight-loss period.