GLOSSARY

Muscle Protein Breakdown (MPB) is the breakdown of muscle proteins into smaller components during tissue renewal. MPB alone does not quantify lost muscle; concurrent synthesis matters.

Body proteins are continually synthesised and broken down, supporting renewal and tissue quality control. Breakdown is not always harmful, and synthesis is not exclusively muscle enlargement. Food, training and rest can alter both rates; interpretation depends on the tissue and time interval rather than treating either process as uniformly good or bad.

Net balance is synthesis minus breakdown for the same tissue and interval. Short-term positivity means synthesis exceeded breakdown, not that all mass gained is muscle. Whole-body and muscle balances can also differ, so the measured pool and units must be identified before translating a result into a claim about muscle gain.

Free amino acids in blood and cells form a dynamic pool supplied by food, protein breakdown and synthesis of some types. It is not a large dedicated store like glycogen. Tissue protein also has functional roles, so breaking down muscle is not simply a cost-free withdrawal from stored food.

Enough energy and carbohydrate appropriate to training can reduce reliance on amino acids as fuel. Extra protein alone cannot correct every consequence of severe underfeeding. Protein sparing also does not remove dietary protein needs or completely stop normal tissue breakdown; it describes a change in how resources are used.

Amino-acid nitrogen is transferred, reused or excreted; some becomes urea in the liver and is eliminated through the kidneys. The carbon skeleton has separate metabolic fates. This normal process alone does not diagnose kidney injury, although established kidney disease requires an individually appropriate dietary protein plan rather than automatic use of sport targets.

A rise in synthesis over laboratory hours is not identical to guaranteed muscle or strength gain over months. Short-term measurements can reflect repair, remodelling or other adaptations. Long-term progress, training, energy and dietary adherence must accompany acute findings when judging a practical training outcome rather than relying on one favourable time point.