Creatine. Works better than any natural supplement I've ever tried for increasing strength, power, endurance. I remember years ago and I had lifted weights for many years, I had trimmed down and could only do 225 for 10 reps on the bench. Starting taking creatine and in no time, I was doing it for 17 reps. Started testosterone and it went to 20 reps. Eventually topping out at 28 reps before injuries.