Use this comprehensive fitness glossary to revise many of the key concepts and principles related to muscle science, training, and nutrition that are discussed in the various guides on this website.
Cellular metabolism: The physical and chemical processes that occur within muscle cells and other cells that are necessary for function and maintenance.
Adenosine triphosphate (ATP): A molecule in which cells store energy to use in cellular functions. ATP is made during aerobic and anaerobic respiration.
Aerobic respiration: A form of cellular respiration that requires oxygen to produce ATP. ‘Aerobic’ means ‘with oxygen’.
Anaerobic respiration: A form of cellular respiration that does not require oxygen to produce ATP. ‘Anaerobic’ means ‘without oxygen’.
Lactate: An acid that is produced in muscle cells as a by-product of anaerobic respiration.
Metabolic acidosis: The lowering of a muscle’s pH level during anaerobic exercise as a result of the accumulation of lactate and hydrogen ions. Causes muscle fatigue.
Muscle fatigue: The decreased capacity or complete inability of a muscle to contract normally, as caused by metabolic acidosis.
Mitochondria: Cellular organelles in which aerobic respiration occurs.
Muscle fiber: One of the cells that make up a muscle. Muscle fibers are cylindrical and multinucleate (have multiple nuclei), and they contract when stimulated.
Type I muscle fibers (aka slow-twitch muscle fibers): Muscle fibers that are used for low-intensity, aerobic activities, such as jogging and lifting very light weights. They have high endurance, contract relatively slowly, and do not tire easily.
Type IIa and Type IIb muscle fibers (aka fast-twitch muscle fibers): Muscle fibers that are used for high-intensity, anaerobic activities, such as sprinting and lifting heavy weights. They have low endurance, contract relatively rapidly, tire easily, and can generate relatively high levels of tension.
Motor neuron: A nerve cell that prompts muscle fibers to contract.
Motor unit: A motor neuron and the muscle fibers that it activates.
Neuromuscular adaptation: The adaptations that your nervous system and muscles experience when you first start weight training that improve muscle-fiber recruitment and optimize the use of existing muscle mass.
Muscular size: A muscle’s diameter.
Muscular endurance: A muscle’s ability to keep contracting against resistance.
Muscular strength: The amount of force a muscle can produce.
Muscular power: A muscle’s ability to rapidly generate force.
Atrophy: The gradual wasting of a muscle that occurs when you stop training.
Hypertrophy: The scientific term for muscular growth.
Agonist: A muscle that is primarily responsible for bringing about a movement.
Antagonist: A muscle that acts in opposition to the agonist.
Synergist: A muscle that assists another muscle to accomplish a movement.
Stabilizer: A muscle that contracts with no significant movement in order to maintain a posture.
Stretch reflex: A reflex that makes muscles contract if rapidly stretched. Initiated by receptors in the muscles called muscle spindles, the stretch reflex prevents muscles from getting damaged due to overstretching.
Autogenic inhibition: A reflex that makes muscles relax when tension is excessive. Initiated by receptors in the tendons called Golgi tendon organs (GTOs), autogenic inhibition prevents muscles and tendons from getting damaged due to excessive forces.
Strength training: Any physical exercise that involves contracting your muscles against resistance with the aim of muscular development. Also known as resistance training. Weight training is the most popular form of strength/resistance training.
Repetition or ‘rep’: One complete unit of a weight training exercise, from the starting position to the point of maximum contraction and then back to the starting position. Can be divided into two phases: concentric (lifting) and eccentric (lowering).
Set: A group of reps. For example, if you perform ten reps before resting, the ten reps will count as one set.
Form: The specific technique that should be used when performing an exercise that ensures maximum results and safety.
Range of motion (ROM): The full range of motion that a joint is capable of making.
Tempo: The speed at which reps are performed.
One-repetition maximum (one-rep max or 1RM): The heaviest weight that you can lift for one, and only one, repetition using proper form.
Isolation exercise: An exercise that involves only one joint (or one pair of joints).
Compound exercise: An exercise that involves two or more joints (or pairs of joints).
Pull exercise: An exercise in which the target muscle contracts when the weight is pulled towards the body.
Push exercise: An exercise in which the target muscle contracts when the weight is pushed away from the body.
Primary exercise: The main and/or most beneficial exercise of the workout, usually a major compound exercise performed at the beginning.
Assistance exercise: A compound exercise that helps the individual to improve his or her primary exercise. Usually a less intense variation of the primary exercise.
Auxiliary exercise: An isolation exercise that helps the individual to improve his or her primary exercise by strengthening lagging body parts that are important for the primary exercise.
Unilateral exercise: An exercise in which only one side of your body is trained at a time.
Bilateral exercise: An exercise in which both sides of the body are trained at the same time.
Functional exercise: An exercise that gives you functional fitness — that is, the kind of fitness that is useful outside of the gym, in everyday activities. Functional exercises strengthen primal movement patterns.
Primal movement pattern: One of seven fundamental movements that the body can make, including squat, lunge, hinge, twist, pull, push, and gait.
Straight set: A type of set sequence in which the number of reps and the amount of weight being lifted remains the same in each set.
Pyramid set: A type of set sequence in which the number of reps is reduced and the amount of weight is increased in each successive set.
Reverse pyramid set: A type of set sequence in which the number of reps is increased and the amount of weight is reduced in each successive set.
Training to failure: To perform reps until you have to stop due to being unable to maintain either tolerance, tempo (speed), or technique.
Dropset: A type of set in which, after you hit failure, you continue the exercise with a lighter weight without resting.
Assisted set: A type of set in which you seek assistance from a training partner to complete a few more reps after the point of failure.
Rest–pause set: A type of set in which you put the weight down after the point of failure, wait for 15 to 20 seconds, pick the weight back up, and continue until failure again.
Superset: A set sequence in which you perform two exercises that target different muscle groups without resting.
Compound set: A set sequence in which you perform two exercises that target the same muscle group without resting.
Eccentric/Negative set: A type of set using extremely heavy weights in which spotters help you to complete the concentric phases of reps and allow you to complete the eccentric phases by yourself.
Pre-exhaustion training: The act of partially exhausting the prime mover muscle(s) by performing isolation exercises before moving on to the compound exercises. The pre-exhaustion makes the prime movers work harder during the compound movements.
Training program: A plan of the training process that you will follow in order to achieve your goal.
Training frequency: The number of training sessions performed per week.
Training intensity: How heavy the weights are that you are lifting relative to your one-rep max.
Training volume: The number of muscles worked, and the number of exercises, sets, and reps performed in a given period of time, such as per workout or per week.
Split training: Dividing the body into sections and training each section in a different workout.
Training split: The plan of what body parts you will train and when. For example, back and biceps on Monday; chest, shoulders, and triceps on Tuesday; and legs and core on Wednesday.
Periodization: The implementation of specific training phases/periods that involve increasing or decreasing training volume, frequency, and intensity with the aim of stimulating development and allowing recovery.
Macrocycle: A long-term training program that works towards a specific goal, such as modifying body composition or peaking for a competition. Usually a year or more in length.
Mesocycle: A phase of training within the macrocycle, usually lasting 6 to 12 weeks. Each mesocycle incorporates variations in training designed to promote the achievement of the goal of the macrocycle.
Microcycle: A phase of training within the mesocycle, typically lasting only one week. Each microcycle incorporates variations in training designed to promote the achievement of the goal of the mesocycle.
Detraining: The loss of fitness that occurs when you stop training.
Overtraining: Training so much that you experience a decrease in performance or a plateau in results. Usually a sign that training load has exceeded recovery capacity.
Progressive overload: The gradual increase in the stress being placed on the muscle with the aim of stimulating progressive muscular development.
Muscle flushing: The act of performing all exercises for one muscle group before moving on to the exercises of the next muscle group. Allows you to boost the blood flow to that area of the body and ensure that it gets adequate oxygen and nutrients.
Plyometric training: An advanced type of power training designed to improve the muscles’ and tendons’ ability to store and then rapidly release energy.
Stretch-shortening cycle (SSC): The eccentric contraction and stretching of a muscle followed immediately by the concentric contraction and shortening of the same muscle that occurs during plyometric training.
Amortization phase: The transition between the eccentric (stretching) and concentric (shortening) phases of the stretch-shortening cycle.
Valsalva maneuver: A breathing technique that involves momentarily holding your breath to brace your core during heavy lifts.
Excess post-exercise oxygen consumption (EPOC): A measurable increase in metabolic rate and oxygen consumption that can persist for several hours after exercise.
Dynamic stretching: The act of performing fluid, controlled movements that take your joints safely through their full range of motion without stretching the muscles. Often performed at the start of a workout as part of the warmup.
Static stretching: The act of holding a stretched position for up to 30 seconds in order to elongate the muscle. Often performed at the end of a weight training workout.
Cardiorespiratory training (aka cardiovascular training or cardio): A type of training that improves endurance and the efficiency of the cardiorespiratory system (heart, blood vessels, lungs, diaphragm, and breathing muscles).
Aerobic training: Low- to moderate-intensity exercises, such as jogging, that can be sustained by aerobic respiration.
Anaerobic training: Vigorous-intensity exercises, such as sprinting, that can only be sustained by anaerobic respiration.
Maximum heart rate: The maximum number of times your heart can beat per minute.
Resting heart rate: The number of times your heart beats per minute while you are at rest.
Heart rate reserve: The difference between your maximum heart rate and resting heart rate.
Training zone: A predefined level of exercise intensity, usually defined based on a range of either maximum heart rate or heart rate reserve.
Rating of perceived exertion (RPE): A numerical rating that you can use to subjectively estimate your level of exercise intensity, usually ranging from 1 to 10 or 6 to 20.
Lactate threshold: The point of exercise intensity at which hydrogen ions and lactate are produced faster than they can be processed, leading to muscle fatigue.
VOmax (aka aerobic capacity): The maximum amount of oxygen that your body can utilize during exercise.
Steady-state training: A type of cardiorespiratory training that involves performing an exercise (such as jogging) at a prescribed intensity for a prescribed period of time.
Interval training: A type of cardiorespiratory training that involves alternating between different training zones in the same workout.
High-intensity interval training (HIIT): A type of interval training that involves alternating between maximal-intensity and lower intensity exercise.
Circuit training: A type of cardiorespiratory training that involves performing a series of different exercises with little to no rest between them.
Nutrition: The study of dietary requirements for proper health and development. Also, the process by which organisms take in and utilize food materials.
Nutrient: A substance that is essential for life and health, providing energy and building blocks for growth, repair, and maintenance.
Micronutrient: A nutrient that is required in small amounts. The micronutrients are vitamins and minerals.
Macronutrient: A nutrient that is required in large amounts. The main macronutrients are carbohydrate, protein, and fat.
Carbohydrate: The macronutrient that constitutes your body’s main source of energy. Three main types are found in foods: sugars, starches, and fiber.
Glucose: A simple carbohydrate and the most important sugar in human metabolism, serving as a primary source of energy. It is absorbed readily into the bloodstream, where it is referred to as blood sugar.
Glycemic index (GI): A measure of a carbohydrate-containing food’s ability to raise blood sugar (glucose) levels after being eaten. All foods containing carbohydrate are ranked on an index from 0 to 100. The GI of pure glucose is 100.
Glycogen: The main storage form of glucose, primarily made and stored in the cells of the liver and muscles.
Protein: A macronutrient that plays a central role in biological processes and forms the basis of living tissues.
Amino acids: The building blocks of proteins.
Essential amino acids (EAAs): Amino acids that the body can’t make and must therefore acquire through the diet.
Non-essential amino acids: Amino acids that the body can usually make using other amino acids.
Biological value (BV): A measure of a protein’s essential amino acid (EAA) content. When a protein contains EAAs in a proportion similar to that required by the body, it has a high BV.
Dietary fat: A macronutrient and an important source of fuel for the body, made of fatty acids. Necessary for the structure and proper function of body cells. Essential for the production of the muscle-building hormone testosterone.
Saturated fat: A type of fat in which the fatty acids all have single bonds. Considered to be a little less healthy than unsaturated fat. Occurs in higher quantities in animal products.
Unsaturated fat: A type of fat in which there is at least one double bond within the fatty acid chain. Occurs in higher quantities in plant products.
Vitamin: Any of various organic substances that are essential in minute amounts for normal growth and activity of living organisms. Found in minute amounts in foods and also produced synthetically. Vitamin deficiencies can lead to disorders.
Dietary mineral: An inorganic element, such as calcium, iron, potassium, sodium, or zinc, that is essential for cellular metabolism, growth, and maintenance.
Whey powder: A milk-derived supplementary source of protein that is digested quickly by the body and provides all nine essential amino acids.
Casein powder: A milk-derived supplementary source of protein that is digested slowly by the body and provides all nine essential amino acids.
Creatine powder: A performance-enhancing supplement that helps your muscle cells to synthesize the energy-containing molecule ATP, used to fuel cellular functions.
Kilocalorie (kcal): A unit of energy found in food. One kilocalorie contains enough heat energy to increase the temperature of 1 kilogram of water by 1 degree Celsius at a pressure of 1 atmosphere. Equivalent to 1,000 calories. Note that the calories in foods are actually kilocalories. In other words, if the food is labeled as having 250 calories, it means that the food contains 250 kilocalories. Often, ‘calorie’ is written with a capital letter (i.e. ‘Calorie’) to mean ‘kilocalorie’ and to distinguish it from the small calorie.
Basal metabolic rate (BMI): The lowest metabolic rate experienced while an individual is at complete physical and mental rest.
Resting daily energy expenditure (RDEE): A less strict and less accurate measure than BMI of the number of kilocalories your body burns at rest.
Total daily energy expenditure (TDEE): The total number of kilocalories your body needs each day to fuel all of your bodily functions and physical activities.
Bulking: A period during which you consume an excess of kilocalories to maximize muscular growth.
Cutting: A period during which you consume fewer kilocalories than your body needs with the aim of losing body fat.
Maintaining: A period during which you consume the amount of kilocalories your body needs to maintain the same weight.
Fat mass: All of the fat in your body, usually expressed as body-fat percentage.
Fat-free mass (aka lean body mass): All of the constituents of your body (bone, muscle, etc.) except fat. Usually used to denote muscle mass.
Hydrostatic weighing (aka hydrodensitometry): The most accurate method of measuring body-fat percentage. Involves being weighed both outside and inside of water and calculating the body’s density by comparing the difference between the two measurements.
Bioelectrical impedance analysis (BIA): A common but unreliable method of calculating body-fat percentage that involves standing on a specialized scale that sends an electrical current through your body and measures the resistance (impedance) experienced by the current.