There’s little doubt that the leg press generates a quadriceps-dominated contraction. Recently, Japanese scientists measured electromyographical (EMG) activity in the medialis and lateralis during the leg press. They measured narrow (feet nearly together), normal (shoulder-width) and wide (wider than shoulder-width) stances, and the results were intriguing. Regardless of foot position, the EMG revealed that while both muscle sections were activated, the vastus medialis (remember, the teardrop) showed greater electrical activity than the vastus lateralis (the outer sweep). The vastus medialis showed greatest electrical activity when the narrow stance was used. Message: Alter your foot width to increase or decrease action on the lateralis and medialis.
Conversely, the leg press produces little involvement in the hamstrings. Using EMG testing, scientists at the American Sports Medicine Institute found no co-contraction of hamstrings and quadriceps during the horizontal leg press. To generate hamstring/glute contraction, the upper body must move toward the knees during a rep, as it does during a squat. With the horizontal leg press, however, the torso remains stationary. Though it does extend forward a bit in the 45-degree version, because the torso remains stationary against and supported by the backrest, minimal hamstring involvement and adaptation take place there as well.
To increase hamstring involvement, place your feet higher on the platform, which brings your upper torso farther forward, approximating a squatting action. But this won’t build up the hamstrings enough to balance front and rear thigh development. (If you choose this route, include lying and seated leg curls in your leg program to offset the developmental disparity.)
Hit All 4 Quad Heads with the Squat
Unlike most other lower-body exercises, the squat places dramatic metabolic demands on the entire body. From flexion to extension, squatting engages three very large muscle groups — the quadriceps, hamstrings and glutes. During the downward or eccentric phase of a rep, the hams and glutes contract eccentrically to control the forward movement of the torso as a result of hip flexion; during the upward or concentric phase, these muscles contract concentrically, with an assist from the paraspinals, to extend the hips and torso.
While your body is doing its damnedest to stabilize each rep, a number of other muscles are working isometrically. The traps and rhomboids help hold the bar while the abs increase intra-abdominal pressure as a means of protecting the spine. And don’t forget the spinal stabilizers themselves, along with other smaller groups — up to 240 muscles in all — contracting to help you squeeze out one eye-popping rep after another. Metabolic demands, indeed. Uncomfortable? You bet.
But look at the cost of temporary discomfort vs. the benefits. Performed correctly, squats provide significantly greater all-around benefits than all other lower-body exercises. The squat ultimately generates the most powerfully involving co-contraction between the quads and hamstrings — neither the hack nor the leg press can do as much for overall development. And it’s the only exercise to nail all four muscle sections of the quadriceps with adequate intensity to maximize muscle gains. Period.
