Working up to 90% or more of your 1RM repeatedly in the same exercise with no variations is a surefire way to backslide in your gains. Luckily, there are ways around this.
Many lifters simply don't go that heavy that often and train submaximally for strength, which can be done with great effectiveness. There are examples of guys training in the 60-80% range for years on end who make gains in strength. They'll consistently work on producing maximal force and using optimal technique with weights hundreds of pounds less than their competition max, enter a short, heavier peaking cycle with weights approaching those that they will use in competition, and then compete and set PRs.
The other solution is to put slight variations into the movements, such as the lifters at Westside Barbell will do. They will work to a max for the upper and lower body once a week, but they change the exercise slightly so as to avoid stagnation. It can be as big as maxing on squats one week and deadlifts another week, or as subtle as changing the height of the deadlifts or changing the bar that they squat with.
People will tell you one is better than the other, but it really boils down to how you want to train and what your body responds to. And sometimes, you can follow these rules above and still end up getting beat up, if that's the case you'll have to deload or reset your weights and start again, which isn't the end of the world.
