Effective exercise is more important than load of exercise.
How heavy is too heavy? Regardless of the number of reps you’re logging or particular move you’re attempting, sometimes the weight is simply not safe or appropriate for you.
Are you lifting too heavy? Here’s how to know:
Unable to load and unload the weight properly. You should be able to lift the weights off the rack and move, with proper mechanics, into your starting position. The same applies to racking the weight after your set is complete.
Unable to maintain proper form. You should be able to stabilize your body against the weight throughout the entire range of motion.
Unable to control the speed of the exercise. You should be able to stop the move at any time during your range of motion. Controlling the weight, rather than using momentum, is key.