Z-line – The boundary between sarcomeres in a muscle fibre, where actin filaments anchor and contractile force is transmitted.

Z-disc – A dense protein structure at each end of a sarcomere that helps maintain the alignment of thin filaments during muscle contraction.

Zone of proximal development (ZPD) – A learning theory describing the gap between what a learner can do independently and what they can achieve with guidance, applied in coaching and skill acquisition.

Zone defence – A tactical strategy in team sports where players cover designated areas rather than specific opponents.

Zone training – A method of prescribing exercise intensity based on heart rate or metabolic thresholds (e.g. aerobic, anaerobic zones).

Zinc – An essential trace mineral involved in immune function, tissue repair, and enzymatic activity, relevant for athlete health and recovery.

Zigzag run test – An agility test assessing the ability to change direction at speed, used in fitness profiling.

Zero-sum game – A concept from sport psychology and game theory where one player’s gain is exactly balanced by another’s loss.

Z-score – A statistical measure used to compare individual performance against a population mean, often applied in fitness testing and data analysis.