GLOSSARY

Metabolic Body Size describes body size transformed to reflect a proposed relationship with metabolic demand. The exponent and purpose must be stated rather than assuming a universal cross-species rule applies directly to every athlete.

Scaling relates a physiological quantity to body size using a specified mathematical model. A simple ratio assumes a particular relationship; an allometric model allows a size exponent that should be justified for the variable and population. Body surface area and surface-area-to-mass ratio also describe geometric features relevant to heat exchange, but do not alone determine cooling or energy requirements. Environmental conditions, body composition and the physiological task must be considered before transferring a scaling rule between species or sports.

A body-composition index expresses a component relative to a body-size measure, often height squared, while a ratio compares specified quantities directly. State both numerator and denominator before interpreting the result. Different skeletal muscle index definitions are used in different settings. A convenient normalization does not automatically remove every body-size effect or establish a sport-specific target. Reference values, measurement method and the population being assessed determine whether a comparison is meaningful.

Body mass and composition can affect the demands of moving the body, but their relationship to performance depends on the task. Absolute strength, power, technique, endurance, skill and recovery may matter differently between sports. Dividing performance by mass can improve a ratio even when absolute performance declines. A nutrition change should therefore be judged against the actual event and health outcomes. There is no universal body-fat percentage or competition weight that guarantees success across athletes.

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.

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.

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.