Ulna – The inner and longer of the two bones in the forearm, important in elbow movement.

Ultramarathon – Any running race longer than the standard marathon distance of 42.195 km.

Ultrasound – A diagnostic imaging technique used to view soft tissue and monitor injury.

Ultraviolet radiation – A component of sunlight that can affect skin health and vitamin D synthesis.

Ultrastructure – The detailed structure within cells, especially muscle fibres, visible under an electron microscope.

Ultra-endurance Events - Events that last more than 6 hours, requiring extreme aerobic capacity and fuelling strategies.

Ultrafine fibre – Muscle fibres with very small diameters, often used in research contexts.

Ultrasonography – The use of ultrasound technology to assess muscle architecture and injury healing.

Unaccustomed exercise – Physical activity that differs from a person's regular routine, often causing DOMS.

Unbalanced force – A force that causes a change in motion, essential in understanding mechanics.

Unconscious competence – The stage of skill learning where performance is automatic and efficient.

Undertraining – Insufficient training stimulus to improve or maintain performance.

Underrecovery – Inadequate time or strategy for physiological repair between training sessions.

Undulating periodisation – A training model that varies intensity and volume frequently to maximise adaptation.

Unilateral movement – An action involving one limb or side of the body, often used for balance or rehab.

Unilateral training – Exercises focusing on one side at a time, enhancing symmetry and core stability.

Unipennate muscle – A muscle with fibres arranged on one side of a central tendon (e.g. extensor digitorum longus).

Universal gym – A multi-station weight training machine often used in school or recreational settings.

Unstable surface training – Training on wobble boards or balance discs to enhance proprioception and control.

Upper body – The torso and arms are commonly trained for strength, mobility, and coordination.

Upper cross syndrome – A postural imbalance involving tight chest and neck muscles with weak upper back muscles.

Upper motor neuron – A neuron responsible for initiating voluntary muscle movement from the brain.

Uptake – The absorption or use of substances like oxygen or nutrients into tissues.

Urea – A waste product formed from protein breakdown, used as a marker of recovery or overtraining.

Uric acid – A metabolic byproduct, excess levels of which can indicate poor recovery or nutritional imbalance.

Urinalysis – The testing of urine to detect hydration status or metabolic byproducts.

Urinary output – The volume of urine produced is a valuable indicator of hydration.

Utilisation – The body's ability to effectively use nutrients or oxygen during exercise.

Utility player – An athlete who can perform competently in multiple positions or roles within a team.

Ulnar deviation – Movement of the wrist toward the little finger side, used in various grip sports.

Untrained individual – Someone with a low or no structured exercise history, often used in research comparisons.

Unconscious incompetence – The first stage of skill acquisition, where the learner is unaware of their lack of skill.

Upper limit – The maximum safe or effective threshold for training load or physiological capacity.

Uptake kinetics – The speed at which a substance (e.g. oxygen or glucose) is absorbed and used by the body.

Upregulation – An increase in the number or activity of receptors in response to demand or training.

Upper extremity – The anatomical term referring to the shoulder, arm, forearm, wrist, and hand.

Unloading phase – The reduced-intensity segment in a training plan that promotes recovery and supercompensation.

Ulnar nerve – A nerve running along the inner arm, important in hand and grip function.

Unconscious movement – Automatic motor control, such as reflexes or deeply learned patterns.

Ultra-processed food – Highly refined food products are often low in nutrient density, affecting athlete health and recovery.

Underwater weighing – A method of measuring body composition based on body density.

Ureters – Tubes that transport urine from the kidneys to the bladder, indirectly related to hydration science.

Urge suppression – The ability to delay physiological needs, such as toileting, during long competition or endurance events.