To build muscle you need to push the volume and intensity to keep the gains coming. Problem is, there's only so much you can tolerate, especially if you take into consideration all the competing demands outside the gym. Once you identify what's best for you, you're set. Ride that wave.
Typically, "gains" – positive adaptations to all that volume and intensity – slow down the closer you get to your goal. That's not inherently a bad thing. It just means your body has become more efficient.
This is where strategically applying a little novelty comes in handy. But this isn't novelty for the sake of novelty. Remember, variety is the spice of life, not the entree. The "law of repeated bouts" still heavily applies, but a timely change up can serve you well.
For the leg press, a simple but brutal way to keep things fresh is to attach bands to each side of the sled. This subtle modification markedly affects the level of force required to complete each rep.
With the bands, as you push the weight up it becomes increasingly harder. This allows for a greater muscle-building stimulus because you're getting the most tension where it typically decreases on the leg press – near full extension.
Warning: This is going to hurt. And you're going to love it.