Deceleration – A decrease in speed or the rate at which movement slows down.

Decision making – The process of choosing the best action in response to a situation during performance.

Dehydration – A condition where the body loses more fluid than it takes in.

Delayed onset muscle soreness (DOMS) – Muscle pain and stiffness occurring 24–72 hours after unfamiliar or intense exercise.

Deltoid – The shoulder muscle responsible for arm abduction and shoulder movement.

Dendrite – A branch-like extension of a neuron that receives electrical signals.

Depolarisation – A change in a cell’s electrical charge that triggers nerve or muscle activation.

Descending motor pathway – Nerve pathways that carry movement commands from the brain to muscles.

Diabetes – A metabolic disease affecting the body’s ability to regulate blood sugar levels.

Diaphragm – A dome-shaped muscle that plays a key role in breathing.

Diastolic pressure – The blood pressure in the arteries when the heart is relaxed between beats.

Diffusion – The passive movement of molecules from an area of high concentration to an area of low concentration.

Digital coaching – Using technology and apps to support and guide athletic training and performance.

Discreet skill – A skill with a clear beginning and end, like throwing a ball.

Dislocation – When a bone is forced out of its normal joint position.

Displacement – The shortest distance and direction from start to finish in a movement.

Distance – The total path travelled regardless of direction.

Divergent thinking – Generating multiple solutions or strategies to solve a performance problem.

Dopamine – A neurotransmitter associated with reward, motivation, and focus in performance.

Dose-response relationship – The link between the amount of training and the body's resulting adaptation.

Double-blind study – A research method where neither the participants nor experimenters know who receives the treatment.

Downward rotation – Movement of the scapula as the shoulder returns from raised to resting position.

Drag – The resistance experienced by a body moving through fluid or air.

Drop jump – A plyometric exercise involving stepping off a box and immediately jumping.

Dropout – When a participant or athlete stops taking part in a training programme or study.

Dual-task training – Performing two tasks simultaneously to improve coordination or decision-making.

Dynamic balance – The ability to stay stable while moving.

Dynamic flexibility – The ability to move joints through their range of motion with control and speed.

Dynamic equilibrium – A state where the body maintains balance while in motion.

Dynamic movement – A movement that involves motion, often requiring strength and coordination.

Dynamic stability – The ability to maintain joint and postural control during active movement.

Dynamometer – A device used to measure muscular strength.

Dystrophy – A disorder causing gradual muscle weakness and loss of muscle tissue.

Dyskinesia – Abnormal or impaired voluntary muscle movements.

Dyslipidaemia – An unhealthy level of fats (lipids) in the blood.

Dyspnea – Difficulty or discomfort in breathing, often during intense exercise.

Duty of care – The legal obligation to ensure the safety and well-being of others.

Delayed feedback – Information given after a skill has been performed.

Developmental age – The stage of physical or emotional maturity, not always the same as chronological age.

Diuretic – A substance that increases urine production, sometimes misused to lose weight quickly.

Dissociation strategy – Focusing away from bodily sensations to reduce discomfort during exercise.

Distal – Farther from the origin or attachment point of a limb to the body.

Disuse atrophy – Muscle loss due to inactivity, injury, or immobilisation.

Directional terms – Terms used to describe the position of body parts (e.g., anterior, posterior, medial).

Data collection – Gathering measurements or observations for analysis in sport science.

Data validity – The extent to which data accurately reflects what it aims to measure.

Data reliability – The consistency of measurement results when repeated under the same conditions.

Developmental coordination disorder (DCD) – A condition affecting motor skill development, sometimes called dyspraxia.

Dominant hemisphere – The side of the brain typically responsible for language and fine motor control.

Dorsiflexion – Lifting the foot upward toward the shin.