Fitness glossary

Updated : July 15, 2026

Deficit, TDEE, RPE, hypertrophy, NEAT… Fitness loves its jargon, and that's often what puts people off at the start. Here are the terms that actually come up, explained in a few clear sentences — no filler, with the numbers that matter.

Nutrition and calories

BMR (basal metabolic rate)

The energy your body burns at complete rest, just to keep you alive: breathing, pumping blood, holding your temperature. It's your theoretical floor, before you move at all. It's calculated from your weight, height, age and sex.

TDEE (total daily energy expenditure)

Your BMR multiplied by your activity level, plus your workouts. It's what you actually burn in a day — your maintenance point. Everything starts here: eat below it to lose fat, above it to build muscle.

Calorie deficit

Eating less than you burn. It's the one non-negotiable condition for losing fat — no 'fat-burning' food gets around it. A deficit of about 20% of your TDEE is the sweet spot: steady progress without wrecking your energy or your muscle.

Calorie surplus

Eating above your expenditure, to give your body material to build muscle. A light surplus (~10%) is plenty: beyond that you don't build faster, you just store more fat.

Maintenance

The calorie level where your weight holds steady: you eat exactly what you burn. It's the most underrated phase — knowing how to maintain is what stops you regaining everything you lost.

Macros (macronutrients)

The three families that make up your calories: protein, carbs, fat. Two people can eat the same calories and get very different results depending on this split — which is why you track them, not just the total.

Protein

The building blocks of muscle, and the most filling macro. Aim for around 2 g per kilo of bodyweight when losing fat (to protect muscle) and 1.8 g/kg otherwise. 4 kcal per gram. Beyond ~2.2 g/kg, no proven extra benefit.

Carbs

Your training fuel. They don't make you fat by themselves — total calories decide that. They fill whatever is left once protein and fat are set. 4 kcal per gram.

Fat

Essential for hormones and vitamin absorption: cutting them to zero is a bad idea. Aim for the greater of 28% of your calories or 0.6 g per kilo. 9 kcal per gram — the densest macro, which is why it's worth counting.

Mifflin-St Jeor

The reference formula for estimating your basal metabolic rate, more reliable than the older Harris-Benedict. It's what dietitians use, and what runs inside Kaizmax. It's still an estimate: real expenditure varies by about 10% between people.

Cutting

A fat-loss phase where you keep as much muscle as possible: moderate deficit, high protein, keep lifting. The word sounds intense, but it's just a well-run deficit — not starvation.

Bulking

A muscle-building phase in a calorie surplus. The smart version is a light, progressive surplus; the 'eat everything' version just adds fat you'll have to lose later.

Body recomposition

Losing fat and gaining muscle at the same time. It's realistic mostly for beginners, people returning after a break, or those with a lot of fat to lose. For advanced lifters it's slow — alternating phases works better.

NEAT

All the energy you spend outside of exercise: walking, taking the stairs, fidgeting, standing. It's often far more than your workouts, and it drops without you noticing when you're in a deficit — one of the real causes of plateaus.

Training

Hypertrophy

The increase in the size of your muscle fibres — in other words, building muscle. It needs three things: enough mechanical tension, volume, and progression over time.

Progressive overload

The single most important principle in strength training: to progress, you must ask a bit more of your body over the weeks — more load, more reps, more sets, or better execution. Doing the same session for 6 months gets you nothing.

Set

A group of reps done back to back without rest. '4 × 10' means 4 sets of 10 reps. Your total sets per muscle per week is your volume — the main lever for building muscle.

Rep

One complete execution of a movement, from the start position back to it. The 6-12 rep range is a good default for building muscle, but muscle is built across a wide range — 5 to 30 reps — as long as the effort is close to failure.

RPE

Rate of Perceived Exertion: a 1-10 score for how hard a set was. RPE 8 = you had 2 reps left in the tank. It's the simplest way to adjust your loads to how you feel that day, instead of following a plan blindly.

RIR

Reps In Reserve: how many reps you could still have done at the end of a set. 2 RIR = you stop 2 reps short of failure. Working between 0 and 3 RIR is the effective zone for hypertrophy.

1RM

The maximum load you can lift once on a given exercise. It's used as a reference to calibrate sessions (e.g. '75% of 1RM'). No need to actually test it: it can be estimated from a heavy set.

Training volume

The total amount of work: in practice, the number of hard sets per muscle per week. Roughly 10 to 20 sets per muscle per week covers most cases. More isn't always better — you still have to recover.

Full body

A session that trains the whole body. Ideal when you train 2 to 3 times a week: each muscle gets stimulated several times, and missing a session costs less than with a split.

Split

Splitting your week by muscle groups (e.g. upper/lower, or push/pull/legs). Worth it from 4 sessions a week; below that, full body is usually more effective.

Push / Pull / Legs

A classic three-way split: push (chest, shoulders, triceps), pull (back, biceps), legs. Easy to organise and easy to run twice a week if you train 6 times.

Deload

A deliberately lighter week (less volume or load) to let your body recover. It's not laziness: it's what lets you come back stronger instead of stalling or getting injured.

DOMS (muscle soreness)

The muscle pain that shows up 24 to 72 hours after a session, especially after a new movement or lots of eccentric work. It is NOT a measure of how good your session was: you can progress perfectly well without ever being sore.

Training to failure

The point where you can't do another rep with good form. Useful occasionally, but going there on every set costs a lot of recovery for marginal gain — most sets are better stopped 1 to 3 reps short.

Cardio (LISS / HIIT)

LISS = continuous low-intensity work (brisk walking, easy cycling). HIIT = alternating very hard efforts and recovery. HIIT takes less time; LISS is less fatiguing and stacks better with lifting. Neither is mandatory for fat loss — the deficit decides that.

Range of motion (ROM)

The range your joint travels, from full stretch to full contraction. Training through a full range builds more muscle than heavier half-reps — ego is expensive here.

What's next?

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Dig deeper: the macro calculation method, holding a calorie deficit, all the Kaizmax guides.