How to pick your first set's weight without guessing

You're standing in front of the machine with no idea whether to load 20 kg or 40 kg. Guess high and the first set flattens the rest of the session; guess low and you grind out fifteen reps wondering what the point was. There's a short procedure that hands you the number instead, and once you have it you keep it.

Your first set isn't a working set

The common mistake is treating set one as if it were the only set. It has a different job: to tell you how the weight feels today, and to get the joints, tendons and nervous system ready for what comes next.

So the first set is deliberately too light. On a machine, two prep sets usually cover it. With a barbell, make it three or four — more muscles are involved and the technique asks more of you. On the big lifts that warm-up isn't wasted time, it's part of the exercise.

The three-step warm-up

The method barely changes from exercise to exercise. Start with the lightest option available — empty bar, lowest plate on the stack, lightest dumbbells — and do 8 to 10 slow reps with full attention on the path of the movement.

Add roughly a third and do 5 reps. Add the same again and do 3. That third set already sits close to your working weight, and it's where you first feel the difference between a load that moves itself and one that asks something of you.

An example: you think your working weight is around 50 kg. Run 20 kg × 8, 30 kg × 5, 40 kg × 3, then 50 kg for your planned reps. The whole thing takes five minutes because the rests are short, 30 to 60 seconds. These sets are meant to prepare you, not tire you.

How you know you got it right

The measure that works best early on is reps in reserve. If you're aiming for 10 reps, the right weight is one you could have taken to 12 or 13 — you finish with two or three reps left in the tank.

The practical signs: the last two reps move visibly slower, but nothing about the technique changes. No hip jerk, no arched back to save the lift, no shortened range. The moment the movement starts changing shape to get the weight up, it's too heavy for you today.

If you finish completely fresh and could clearly do another five or six, it's too light. Not a disaster — add load and go again, and start from the higher number next time. There's a fuller breakdown of the arithmetic in the piece on how much weight to put on the bar.

When you've never done the exercise before

The first time you meet an exercise, guessing is pointless. Take the lightest version, do 10 clean reps, add the smallest available increment and repeat. Keep going until you reach a load that demands attention.

Your first session can end up being mostly number-hunting, and that's fine — it's what that session is for. It's better to leave with a page of numbers and no soreness than with soreness and no data. If you're still working out what the whole session looks like, see what a first gym session involves, step by step.

Jumps aren't the same on every exercise

Big leg and back lifts tolerate bigger steps: 5 to 10 kg is often perfectly reasonable. Upper-body presses want smaller ones, 2.5 to 5 kg. Isolation work — lateral raises, curls, triceps extensions — needs 1 to 2.5 kg, because five kilos there can be the difference between ten reps and three.

Machines are deceptive. Plates on a stack aren't always the value printed on them, and levers and pulleys differ between machines, so a number from one doesn't transfer to another even when both target the same muscle. The number you write down belongs to that machine in that gym.

Dumbbells have their own catch: each side stabilises itself, so the combined load is usually lower than the barbell version of the same movement. Don't assume a 40 kg bench press means two 20 kg dumbbells.

When you realise mid-set that you're wrong

If it's too heavy and the second or third rep already looks ugly, stop the set. There are no points for finishing with bad technique. Strip 10 to 20 per cent off and do it properly.

If it's too light, finish the set, add weight, and count it as another prep set rather than a working set. Otherwise you'll come back next week thinking you did more volume than you actually did.

Write the number down

You only do this whole process once per exercise. After that you own a number and you don't start from scratch. Record the weight, the reps and how it felt — a single word does the job: easy, right, hard.

That's the case for keeping a training log. Without one you go hunting for the same number every few weeks. And when the same weight feels easy two sessions in a row with clean technique, that's your cue to look at when to add load.

When to see a doctor

Muscle soreness a day or two after training is expected, and the piece on what normal training soreness is covers where the line sits. Sharp pain that arrives at the moment of the lift, joint pain lasting days, swelling, pins and needles or weakness in an arm or leg are not part of the process and need looking at.

The same goes for chest pressure, severe dizziness or breathlessness at moderate effort. If you have a known heart or blood pressure condition, or a previously operated joint, agree the limits with a doctor before you go looking for your maximums.

The short version

• Set one is information, not training — start from the lightest option available.
• Warm up in three steps: 8 reps light, 5 moderate, 3 close to working weight, with 30–60 second rests.
• The right working weight leaves 2–3 reps in reserve and doesn't change your technique.
• Jumps: 5–10 kg on legs and back, 2.5–5 kg on presses, 1–2.5 kg on isolation work.
• Log the weight and how it felt, so the next session starts from a number rather than a guess.