Radial artery – A major blood vessel in the forearm commonly used to measure pulse.

Radiograph – An image produced by X-rays, often used to assess bone injuries.

Range of motion (ROM) – The extent of movement possible at a joint.

Rate coding – The frequency of nerve impulses sent to muscle fibres to control force output.

Rate limiter – A factor that slows or restricts motor development or skill acquisition.

Rate of force development – The speed at which force is generated during a muscular contraction.

Rating of perceived exertion (RPE) – A subjective scale used to measure exercise intensity.

Reaction time – The time taken between a stimulus and the initiation of a response.

Rebound – The act of recovering the ball after a missed shot in sports like basketball.

Receptor – A structure that detects stimuli and sends signals to the nervous system.

Reciprocal inhibition – A process where activation of one muscle inhibits its opposing muscle.

Recovery – The period after exercise when the body returns to homeostasis and adapts to training.

Recovery heart rate – The rate at which the heart returns to resting levels after exercise.

Recruitment – The activation of additional motor units to increase muscle force.

Rectus abdominis – A major abdominal muscle responsible for trunk flexion.

Rectus femoris – One of the quadriceps muscles, contributing to both hip flexion and knee extension.

Red blood cell – A blood component that transports oxygen from the lungs to the tissues.

Red muscle fibre – Slow-twitch fibres that are fatigue-resistant and suited for endurance activities.

Reflex – An automatic response to a stimulus controlled by the spinal cord.

Reflection – A process of evaluating past experiences to improve future performance or teaching.

Refraction – The bending of light through the eye, relevant in visual tracking during sport.

Refractory period – The time after a nerve impulse when another cannot be generated.

Regression analysis – A statistical technique used to predict one variable based on another.

Rehabilitation – The process of restoring function after injury through structured therapy.

Relative intensity – The difficulty of an activity relative to a person's maximum capacity.

Relative VO₂ max – Maximal oxygen uptake adjusted for body weight (mL/kg/min).

Reliability – The consistency and repeatability of a measurement or test.

Remote coaching – Delivering training plans and feedback via online or digital platforms.

Renal function – The ability of the kidneys to regulate water and electrolyte balance, important in hydration.

Repetition – A single performance of an exercise movement, such as one push-up or squat.

Repetition maximum (RM) – The maximum number of repetitions a person can complete at a specific load.

Residual volume – The air remaining in the lungs after a maximal exhalation.

Resistance training – Exercise that uses resistance (e.g. weights or bands) to build strength or endurance.

Resistance band – A portable tool providing variable resistance during strength exercises.

Resisted sprint – A sprint drill with added load to increase power and acceleration.

Respiration – The process of gas exchange in the lungs and tissues to produce energy.

Respiratory exchange ratio (RER) – A measure of substrate use during exercise (carbohydrates vs fats).

Respiratory muscles – The muscles involved in breathing, including the diaphragm and intercostal muscles.

Respiratory rate – The number of breaths taken per minute.

Respiratory system – The body system responsible for gas exchange and oxygen delivery.

Rest interval – The amount of time allocated for recovery between sets or exercises.

Resting heart rate – The number of heartbeats per minute at complete rest.

Resting metabolic rate (RMR) – The amount of energy expended by the body at rest.

Resting potential – The electrical charge across a nerve or muscle cell when inactive.

Retention – The ability to remember and reproduce a skill after practice has stopped.

Retraining – The process of regaining fitness or skill after a period of inactivity.

Retroactive interference – When new information disrupts the recall of previously learned skills.

Reversibility – The principle that fitness gains are lost when training stops.

Revolutions per minute (RPM) – A measure of cycling or rotational speed.

Rhabdomyolysis – A serious condition involving muscle breakdown and the release of harmful proteins into the blood.

Rib cage – The bony structure protecting the lungs and heart, important in breathing mechanics.

RICE – An acronym for Rest, Ice, Compression, Elevation; a basic treatment for acute injuries.

Risk assessment – The process of evaluating potential dangers in physical activity or sport.

Risk management – Implementing strategies to reduce the likelihood of injury or harm.

Ritual – A repeated pre-performance behaviour or routine that helps with focus and confidence.

RoM (range of motion) test – An assessment used to measure joint flexibility.

Rotation – Movement around an axis, common in sports like golf and gymnastics.

Rotator cuff – A group of muscles stabilising the shoulder joint.

Roughage – Dietary fibre is important for digestion and overall athlete health.

Route running – A skill in American football involving precise movement patterns.

RPE scale – The Borg scale is used to subjectively rate exercise intensity.

Rugby-specific fitness – The combination of strength, speed, endurance and agility required in rugby.

Run economy – The amount of energy used at a given running speed, important for endurance performance.

Run-up – The approach phase before a skill like a jump or throw.

Running biomechanics – The study of movement patterns and forces during running.

Running gait – The pattern of movement during running, including stride length and foot strike.

Running surface – The type of terrain (grass, track, road) that affects biomechanics and injury risk.

Running volume – The total distance or time spent running in a given period.

Rating of muscle soreness – A scale used to quantify delayed-onset muscle soreness (DOMS).

Recovery modality – A method used to aid post-exercise recovery, such as massage or cryotherapy.

Rate pressure product – An indicator of cardiac workload (heart rate × systolic blood pressure).

Reactivity – The change in performance due to being observed or tested.

Resilience – The ability to bounce back from setbacks, stress, or adversity in sport.

Reactive agility – The ability to change direction in response to an unpredictable stimulus.

Reactive strength – The capacity to rapidly switch from eccentric to concentric muscle action.

Rebound heart rate – The heart rate increases during recovery if recovery is incomplete or overtraining exists.

Relative strength – The amount of force an athlete can produce relative to their body weight.

Refuelling – The post-exercise replenishment of energy stores through nutrition.

Rehydration – Replacing fluids lost during exercise to restore hydration balance.

Running drill – A structured exercise to improve technique, coordination, or speed.

Rule adaptation – Modifying game rules to support learning or inclusivity.

Respiratory alkalosis – A condition caused by excessive breathing, lowering carbon dioxide levels in the blood.

Running-based anaerobic sprint test (RAST) – A field test measuring anaerobic power using repeated sprints.

Reinforcement – A psychological tool used to encourage desired behaviours in sport or training.

Readiness – The physical and mental state that enables successful participation or competition.

Regeneration – The biological process of repairing tissues and restoring function post-exercise.

Relative risk – The likelihood of injury or illness in one group compared to another.

Resisted movement – Any movement performed against a load or opposition.

Resonance frequency – A breathing frequency associated with optimal heart rate variability and recovery.

Re-education – Retraining of movement or technique, often used in rehabilitation.

Reticulospinal tract – A neural pathway involved in postural control and motor coordination.

Radiation (heat loss) – The loss of body heat to the environment without direct contact.

Recovery curve – A graph showing how quickly physiological variables return to baseline after exercise.

Reactive oxygen species – Molecules that can cause cellular damage if not balanced by antioxidants.

Reflex arc – The nerve pathway involved in a reflex action.

Restorative yoga – A gentle form of exercise used for active recovery and stress relief.

Rate of perceived recovery – A scale used to measure how recovered an athlete feels post-session.