If I had to pick one supplement that should be the foundation of your health and longevity goals, I would say, fish oil!! A few things Fish oils do is, improve your cardiac health, mood elevation, inflammation reduction, and even body fat reduction. (YES, Exercising when taking fish oils has shown improved fat loss !!!)  It has also been shown to reduce joint and muscle fatigue, especially seen in those who are working out religiously!!
Over training is REAL and very possible when you are hitting the gym at least 6 times a week and often more than 10x/week when you are preparing for a show or focusing on a structured exercise program to get into the absolute best shape of your life!
I highly suggest you supplement with Fish Oils or better yet a supplement that consists of all your essential fats — Omega 3-6 & 9’s)
Next on the list is glutamine but your essential fatty acids (EFA’s)are #1!!
HENCE WHY THEY ARE CALLED ESSENTIAL!!!