GLOSSARY

BMI-for-Age interprets BMI relative to age and an appropriate sex-specific pediatric reference. Adult fixed categories cannot simply be applied to a growing child or adolescent.

For example, a strength athlete's high body mass relative to height can increase BMI without showing how much of that mass is fat. Use the number as one descriptive measure, then consider relevant assessment and health findings. Applying a general label mechanically can distract from the athlete's actual nutritional needs and performance context.

BMI divides body mass by height squared. It is a screening and population-description measure rather than a direct measurement of body fat, muscle or health. Muscular athletes can have a high BMI without the same adiposity as another person with the same value. Adult classifications do not transfer directly to children, who require age- and sex-appropriate interpretation. Health assessment should consider clinical context, distribution of fat and other relevant findings rather than diagnosing from BMI alone.

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.

Skeletal muscle contributes force and movement, but muscle quantity and performance are not identical. Training quality, neural adaptations, architecture and task specificity matter alongside tissue mass. Resistance exercise and adequate nutrition can support muscle gain or preservation, while energy restriction may make this harder. A larger measured lean compartment does not automatically demonstrate a larger muscle compartment. Interpret body-composition changes alongside strength, function and the demands of the sport rather than using mass alone as the outcome.