Lactic acid – A byproduct of anaerobic glycolysis that can contribute to muscle fatigue during high-intensity exercise.

Lactate – The usable form of lactic acid in the body, often recycled as energy by the liver and muscles.

Lactate threshold – The exercise intensity at which lactate begins to accumulate in the blood faster than it can be removed.

Lactate tolerance – The ability to perform despite rising lactate levels, often improved through interval training.

Lactate shuttle – The process by which lactate is transported between cells to be used as fuel or converted to glucose.

Laminar flow – Smooth, uninterrupted flow of air or fluid, important in understanding aerodynamic and hydrodynamic drag.

Latency period – The short delay between a stimulus and the start of a muscle contraction.

Latent learning – Learning that occurs without immediate performance or reinforcement, often revealed later.

Latissimus dorsi – A large back muscle responsible for shoulder extension, adduction, and internal rotation.
Lateral – A directional term meaning away from the midline of the body.

Lateral dominance – A preference for using one side of the body over the other, such as being right-handed.

Lateral epicondylitis – Commonly known as tennis elbow, caused by overuse of the forearm muscles.

Lateral inhibition – A neurological process that sharpens sensory signals, improving movement accuracy.

Lateral line – A sensory system in aquatic animals that detects water movement, used as a model in biomechanics.

Lateral raise – A resistance training movement targeting the deltoid muscles.

Law of inertia – Newton’s first law stating that an object remains in motion or at rest unless acted on by an external force.

Law of acceleration – Newton’s second law explaining how force equals mass times acceleration (F = ma).

Law of action-reaction – Newton’s third law stating that every action has an equal and opposite reaction.

Lead-up activity – A simplified version of a skill used in practice to build confidence and technique.

Lean body mass – The total mass of the body excluding fat, including muscle, bone, water, and organs.

Learning – A relatively permanent change in behaviour or knowledge due to experience or practice.

Learning curve – A graph showing the rate of learning over time, often showing rapid early improvement.

Learning plateau – A period during learning where no apparent progress is made.

Learning style – An individual's preferred way to process and absorb information, such as visual or kinaesthetic.

Learning transfer – The influence of previously learned skills on the learning of new ones.

Leptin – A hormone produced by fat cells that helps regulate appetite and energy balance.

Lesion – A damaged or abnormal area of tissue, often as a result of injury.

Lever – A rigid structure that moves around a pivot to produce movement, often used to describe bones.

Lever arm – The distance between the axis and the point of force application in a lever system.

Lever classes – The three types of levers (first, second, and third class) based on the position of fulcrum, load, and effort.

Libido – Sexual drive influenced by hormones, sometimes relevant to health and performance monitoring.

Ligament – A band of fibrous tissue that connects bone to bone and stabilises joints.

Limb – An arm or leg, used to perform most movements in sport.

Limit of stability – The furthest a person can lean or shift weight without losing balance.

Linear displacement – The distance in a straight line from a starting point to an ending point.

Linear motion – Motion in a straight line, with all parts of an object moving the same distance.

Linear speed – The rate at which an object moves over a distance in a straight path.

Linear velocity – Speed in a specific direction; an essential concept in biomechanics.

Line of gravity – An imaginary vertical line passing through the centre of gravity to the ground.

Lipid – A type of fat molecule used for long-duration energy production.

Lipolysis – The breakdown of fats into free fatty acids for energy.

Lipoprotein – A molecule that carries cholesterol and triglycerides in the blood, such as LDL and HDL.

Loading – The application of force or stress to the body or joints during movement or training.

Load – The weight or resistance applied to a muscle during training.

Load–repetition relationship – The inverse relationship between load size and the number of repetitions possible.

Loading phase – The portion of a movement where force is absorbed or generated, such as during squats.

Local muscular endurance – The ability of a specific muscle group to sustain contractions over time.

Locomotion – The ability to move from one place to another, such as walking, running, or crawling.

Long bones – Bones that are longer than they are wide, such as the femur and humerus.

Long head (muscle) – Refers to the longer part of a bi-headed muscle, such as the long head of the biceps.

Long-slow distance training – A method of endurance training using continuous low-to-moderate intensity exercise.

Longitudinal axis – An imaginary vertical line around which rotation occurs, such as in a spin.

Longitudinal research – A research design involving repeated observations of the same variables over time.

Long-term memory – The capacity to store information and experiences for extended periods.

Long-term potentiation – A lasting increase in synaptic strength following high-frequency stimulation, key in skill learning.

Loop of Henle – A kidney structure important for regulating water balance and electrolyte levels.

Low back pain – Discomfort in the lumbar spine region, common in athletes with poor posture or weak core.

Low-density lipoprotein (LDL) – Often referred to as "bad cholesterol" due to its role in arterial plaque buildup.

Low-impact exercise – Physical activity that minimises stress on the joints, such as swimming or elliptical use.

Lower crossed syndrome – A postural imbalance involving tight hip flexors and weak glutes or abdominals.

Lower limb – The leg, from hip to foot, essential for locomotion and weight-bearing.

Lumbar spine – The lower back portion of the vertebral column, important for stability and movement.

Lumbopelvic stability – Control of the lumbar spine and pelvis during movement, essential for athletic performance.

Lung – A respiratory organ where oxygen is exchanged with carbon dioxide in the blood.

Lung capacity – The maximum volume of air that the lungs can hold.

Lung compliance – The ability of the lungs to stretch and expand during breathing.

Lung diffusion – The process where gases are exchanged between alveoli and the bloodstream.

Lung volume – A measurement of air within the lungs during different phases of breathing.

Luteinising hormone (LH) – A hormone that stimulates reproductive organs and may influence performance.

Lux – A unit of measurement for light intensity, relevant in facility design and safety.

Lymph – A fluid in the lymphatic system that helps remove waste and support immune function.

Lymphatic drainage – The process by which lymph is circulated and waste products are removed from tissues.

Lymphocytes – White blood cells that support immune responses, often monitored in athlete health screening.

Lysosome – A cell organelle that helps break down waste and cellular debris.

Lysis – The breaking down or destruction of cells, relevant in muscle damage or pathology.

Latent period – The short time between stimulation and the start of a muscle contraction.

Linear acceleration – A change in velocity in a straight line, key in sprint performance.

Linear stability – The ability to maintain or return to a balanced position after being moved in a straight line.

Loading parameters – Variables such as weight, sets, reps, and rest used to structure resistance training.

Load monitoring – Tracking training load to prevent overtraining and optimise performance.

Length-tension relationship – The idea that muscle force depends on the muscle’s length at contraction.

Labrum – A ring of cartilage in joints like the shoulder or hip that provides stability and cushioning.

Lactate clearance – The rate at which lactate is removed from the blood after intense activity.

Lacteal – A structure in the small intestine that absorbs dietary fats into the lymphatic system.

Limbic system – A group of brain structures involved in emotion and motivation, influencing arousal in sport.

Locomotor skills – Fundamental movements such as walking, running, hopping, and skipping.

Load carriage – The act of carrying weight during activity, relevant in military and endurance performance.

Loaded movement – Movement performed while carrying or resisting external weight or force.

Light adaptation – The process by which the eyes adjust to changes in lighting, relevant in outdoor sports.

Live high–train low – A training method where athletes live at altitude but train at sea level for performance gains.

Line judge – An official in sports like tennis or volleyball who determines whether a ball lands in or out.

Left ventricular hypertrophy – Thickening of the heart’s left ventricle due to endurance or strength training.

Lactate dehydrogenase – An enzyme involved in the conversion of lactate to pyruvate in metabolic pathways.

Lab coat syndrome – Increased stress responses when physiological testing is performed in a clinical setting.

Leg press – A resistance exercise that targets the quadriceps, glutes, and hamstrings.

Lat pulldown – A strength exercise that works the upper back and biceps through pulling movements.

Lifting technique – The correct form used during resistance training to prevent injury and improve performance.

Limb length – A measurement that may affect biomechanics, gait, and technique in sport.

Limb velocity – The speed of limb movement, relevant in throwing, kicking, and sprinting.

Load vector – A diagram showing the direction and magnitude of forces applied in movement or lifting.

Ligamentous support – The stabilising role of ligaments in joint mechanics and injury prevention.