This glossary defines 68 training terms in plain English: what each one means, why it matters, and how to actually use it in your workouts. No jargon explained with more jargon. Every entry is written and reviewed by our Chief Exercise Scientist, so the definitions are conservative and grounded in research, not gym folklore.
A
Aerobic Base
Your aerobic base is your foundation of easy-pace endurance: how much low-intensity work your body can absorb, sustain, and recover from.
AMRAP
AMRAP stands for "as many reps as possible" or "as many rounds as possible," depending on context.
Anabolic Window
The anabolic window is the idea that you have 30 to 60 minutes after a workout to eat protein or your gains slip away.
B
BDNF
BDNF stands for brain-derived neurotrophic factor.
Bilateral Deficit
The bilateral deficit is a strange but well-documented quirk: two limbs working together produce less total force than the sum of what each limb can do alone.
BMR (Basal Metabolic Rate)
BMR, or basal metabolic rate, is the number of calories your body burns at complete rest just to keep you alive.
Body Recomposition
Body recomposition is losing fat and building muscle at the same time.
Bone Mineral Density
Bone mineral density is the amount of mineral, mostly calcium, packed into a given area of your bone.
C
Cluster Sets
Cluster sets break one set into small blocks of reps separated by short rests, usually 15 to 30 seconds, all inside what still counts as a single set.
Compound Exercises
Compound exercises are lifts that move two or more joints at once and train several muscle groups in one movement.
Concentric Contraction
A concentric contraction is the lifting phase of a rep: the muscle shortens while producing force.
Cortisol
Cortisol is your body's main stress hormone, released by the adrenal glands to mobilize energy when you're under physical or mental pressure.
Creatine Loading
Creatine loading is taking a high dose, around 20 grams a day split into 4 smaller doses, for 5 to 7 days to fill your muscle creatine stores fast.
Cross-Education
Cross-education is the strength gain that shows up in an untrained limb when you train only the opposite one.
D
Deload
A deload is a planned easy week of training, usually with total work cut roughly in half, that lets weeks of accumulated fatigue fade away.
Detraining
Detraining is the gradual loss of fitness adaptations when you stop training.
DOMS
DOMS stands for delayed onset muscle soreness: the ache and stiffness that shows up 12 to 24 hours after a workout and peaks somewhere between 24 and 72 hours.
Drop Set
A drop set is an intensity technique where you take a set to failure or close to it, immediately cut the weight by around 20 to 30 percent, and keep repping without resting.
E
Eccentric Training
Eccentric training deliberately emphasizes the lowering phase of a lift, the part where the muscle lengthens under load.
EMOM
EMOM means "every minute on the minute." At the top of each minute you start a fixed chunk of work, say 10 kettlebell swings, and whatever's left of the minute is your rest.
EPOC
EPOC stands for excess post-exercise oxygen consumption: the extra oxygen, and the extra calories, your body uses after a workout while it returns to baseline.
Exercise Snacks
Exercise snacks are short bursts of movement, usually one to two minutes of vigorous effort, scattered through your day instead of packed into one formal workout.
G
Gamification
Gamification means applying game mechanics (points, levels, streaks, quests, badges, leaderboards) to something that isn't a game, like exercise.
GLP-1 and Exercise
GLP-1 and exercise refers to how training fits alongside GLP-1 medications like semaglutide and tirzepatide.
Greasing the Groove
Greasing the groove is a strength method where you practice one exercise, classically pull-ups, in frequent easy sets spread across the day, always stopping well short of failure.
Ground Reaction Force
Ground reaction force is the force the ground pushes back with every time your body pushes into it.
H
Habit Stacking
Habit stacking is attaching a new habit to one you already do automatically, using the formula "after I do X, I will do Y." After I brew coffee, I do 10 squats.
Heart Rate Reserve
Heart rate reserve is your max heart rate minus your resting heart rate: the full range of beats your heart can add on top of rest.
HIIT
HIIT, high-intensity interval training, is cardio built from repeated near-maximal efforts, roughly 80 to 95 percent of max heart rate, separated by recovery periods.
HRV (Heart Rate Variability)
Heart rate variability is the tiny variation in time between one heartbeat and the next, measured in milliseconds.
Hypertrophy
Hypertrophy is the growth of muscle fibers in response to training.
I
Insulin Sensitivity
Insulin sensitivity is how readily your cells respond to insulin, the hormone that tells them to pull glucose out of your blood.
Isolation Exercises
Isolation exercises are movements that work one joint and target one muscle at a time.
Isometric Exercise
Isometric exercise is producing muscular force without any movement.
L
Lactate Threshold
Lactate threshold is the exercise intensity where lactate builds up in your blood faster than your body can clear it.
Leucine Threshold
The leucine threshold is the per-meal dose of leucine, roughly 2 to 3 grams, needed to fully switch on muscle protein synthesis.
LISS
LISS stands for low-intensity steady state: continuous cardio done at an easy, unchanging pace you could hold for 30 to 60 minutes while talking comfortably.
M
Macros
Macros, short for macronutrients, are the three nutrients that provide calories: protein, carbohydrates, and fat.
Max Heart Rate
Max heart rate is the highest number of beats per minute your heart can hit during all-out effort.
Mesocycle
A mesocycle is a training block of roughly 3 to 6 weeks organized around one main goal: build muscle, gain strength, improve conditioning.
Mind-Muscle Connection
The mind-muscle connection is deliberately focusing your attention on the muscle doing the work during a rep, feeling it stretch and squeeze, instead of thinking about the weight or just moving it from A to B.
Muscle Memory
Muscle memory is your body's ability to regain lost muscle and strength far faster than it took to build them the first time.
Muscle Protein Synthesis
Muscle protein synthesis (MPS) is the process where your body assembles amino acids into new muscle protein, repairing and building tissue.
N
O
P
Periodization
Periodization is the practice of organizing training into planned phases, each with its own focus and difficulty level, so stress and recovery alternate on purpose.
Polarized Training
Polarized training is a way of distributing cardio intensity: roughly 80 percent of your training is easy, about 20 percent is genuinely hard, and almost none of it sits in the moderate middle.
Progressive Overload
Progressive overload means gradually increasing the demand you place on your body over time, so it has a reason to keep adapting.
Protein Distribution
Protein distribution is how you spread your daily protein across meals.
Push Pull Legs (PPL)
Push pull legs is a training split that sorts the week into three session types by movement pattern.
R
Recovery Score
A recovery score is the single readiness number your wearable spits out each morning.
Rest-Pause
Rest-pause is an intensity technique where you take a set close to failure, rack the weight for 10 to 20 seconds, then keep going with the same load for a few more reps.
RIR (Reps in Reserve)
RIR, or reps in reserve, is the number of extra reps you could still have done when you ended a set.
RPE (Rate of Perceived Exertion)
RPE, or rate of perceived exertion, is a 1 to 10 scale for rating how hard a set felt.
S
Sarcopenia
Sarcopenia is the gradual loss of muscle mass, strength, and function that comes with aging.
Streak
A streak is an unbroken chain of consecutive days (or weeks) completing a habit: working out, hitting a step goal, logging a session.
Superset
A superset is two exercises done back to back with little or no rest between them, followed by one normal rest period.
T
Tabata
Tabata is a high-intensity interval protocol: eight rounds of 20 seconds of all-out work followed by 10 seconds of rest, four minutes total.
TDEE
TDEE stands for total daily energy expenditure: every calorie you burn in a 24-hour day.
Tempo Training
Tempo training assigns a speed to each phase of a rep, usually written as four numbers like 3-1-1-0.
Time Under Tension
Time under tension, or TUT, is the total number of seconds a muscle spends working during a set.
Training Load
Training load is the total stress your training places on your body, usually estimated as volume times intensity over a period of time.
Training to Failure
Training to failure means pushing a set until you genuinely can't complete another rep with good form.