There's a very famous trainer that I know. He trains the rich, the famous, and the superhero body inclined. And this man only uses two supplements to help his clients.
BCAA'S and melatonin. (I won't write about melatonin today, suffice to say it's a natural chemical that our bodies produce to help us sleep)
And there is a reason for that. He pushes his clients hard, and he's able to because of the BCAA'S and their effect on the body.
So what are these things?
BCAA stands for Branch Chained Amino Acids.
Amino acids are extremely essential for building new protein and muscle in your body.
Basically, if you take BCAA'S before and after your workout, you're instantly starting to replace the muscle you have ripped during your workout. This means that you won't be sore the next day and can push yourself harder.
BCAA'S also give you energy since they are chained they act as a kind of long burning fuel, which means there will be less fatigue during your workouts.
They also replace the missing amino acids from your diet. You'd have to eat extreme amounts of protein to not only replace the stuff that you rip during exercise, but to fuel your next exercise, you'd essentially be eating all day (which sounds nice at first, but it's tedious and time consuming)
In summation, BCAA'S fight fatigue, build muscle and replace essential amino acids in your diet so you can workout harder, better, faster... and stronger.