Enough time has passed
When you hit 4 to 8 weeks training with the same weight, it’s time to move on and add more weight to every set.
It’s not hard
You should be straining to complete each set and the final set of each exercise should leave your muscles exhausted. Your body only responds to ‘overworked’ muscles, muscles that work to their very limits.
Muscle fatigue is a sure sign you are doing the right exercises using the right weight. Your goal should be to hit fatigue on the last set of every exercise you do.
You’re not making progress
If you are stuck lifting the same weight for weeks or even months, it means you have stopped pushing yourself and your muscles have stopped adapting.
N.B You don’t have to go all that extra in adding weight on the barbell, just add 2 to 10 kg’s and see the difference.