Warm-up sets are lighter sets with increasing weight that you do before your working sets. They prepare your muscles, joints and technique for the heavy load without tiring you out beforehand.
How to warm up
A proven routine starts with 5 to 10 minutes of easy cardio on a bike, treadmill or rower. Before your first compound lift, do 2 to 4 warm-up sets with increasing weight, for example the empty bar for 10 reps, then about 50 percent for 5, 70 percent for 3 and 85 percent for 1 rep of your working weight. For further exercises, one light set is usually enough.
Example: Your working weight for squats is 100 kg. You warm up with 20 kg × 10, 50 kg × 5, 70 kg × 3 and 85 kg × 1, then start your working sets. The plate calculator shows which plates to load. This is an example.
Why they do not count
Warm-up sets do not count toward your training volume. A hard set is only a working set that ends with at most about 3 reps in reserve. Warm-up sets stay deliberately far from that, below 5 on the RPE scale. If you count them, you overestimate your volume, especially on compound lifts with many steps.
Keep the reps low as you get closer to your working weight. The goal is to be ready, not tired. A true max attempt also requires a warm-up, clean technique and safeties or a spotter.