2. Increase Time Under Tension
Your muscle for the most part has an all or nothing response. Either the fibers contract or they do not, but they do not all contract at 100% capacity every time they contract. You have these motor units that are responsible for contracting muscle fibers. When we increase the time under tension we increase the demand on the fibers which causes the motor units to increase the intensity of the contraction without loading heavier weight. This is done at the weakest point of the lift. You are strongest in the eccentric portion of the movement when you are lowering the weight, but weaker in the concentric portion when you are raising the weight or contracting the muscle.
On the leg press simply use your warm up weight. When I say warm up weight I am speaking about the weight you use to begin your set, which for me is 4 plates each side. I have already spent 5 minutes on the bike, 5 minutes on the eliptical, done some bodyweight squats, and some mobility stretching. After you lower the weight at your normal tempo then press at a much slower tempo. Press the weight back up so slow that you count to 10 before you have completed your rep. A SLOW 10!!! A 10 like those alligators or Mississippi’s you used to count in grade school. And yes I used spell check to write that state that I won’t bother to type again.
Repeat these reps 10-20 times for 5 sets. You will engorge your muscles with blood, enjoy a massive pump, and your fibers will be well on their way to fatigue. Then and only then are you ready to move on to your compound movement of the squat. Now, when you squat, you will not have to go quite as heavy to reach the fatigue required for growth. This means a lighter load for your achey back or knees.