I've been bodybuilding for over 15 years now and a lot has changed since then. I started out at my high school gym and now train in Golds, I use to work out in the evening and now I train before work, I use to take plain creatine monohydrate and now I use BSN Cellmass. Alot has changed, but one thing that hasn't change is the importance of hack squats and how its executed.
Looking away from the machine, stand beneath the resistance pads so they sit on your shoulders. Put your feet hip- to shoulder-width apart and about 11 inches in front of your body.
Keeping your torso upright and your back tight against the pad at all times. Look forward so that your head is in sync with your torso.
Breath in slightly more than normal and hold your breath as you bring your body down into a squat until your thighs are near parallel to the floor.
Continue keeping your breath as you move from the down position to the up postition; pushing forcefully with your legs to make the transition strong but smooth.
Exhale as you pass the most difficult part of the up phase and as you return to the start position.
Maintain your neutral spinal position - a slight arch in the lumbar spine - during the descent and ascent.
If you place your feet directly under your body as in a regular free squat, you'll find it extremely difficult to keep your torso erect and to maintain the arch in your lumbar spine. Your knees may also move out well in front of your feet, placing excessive stress on your knees and conceivably injuring them or your lower back.
It may help to think of the hack squat as a wall squat: Your torso remains erect and you contract your erector spinae (lower-back muscles) to maintain normal spinal curvature throughout the range of motion.
In the free-standing squat, tight hamstrings can rotate the pelvis backward, creating a rounded back that can be very dangerous. The hack squat is very safe - your torso doesn't incline forward, your hamstrings aren't stretched maximally at the hip end, and bending your knees gives the hamstrings slack without rotating your pelvis.
The hamstrings aren't as strongly involved in this exercise as they are in the barbell squat, although squatting deeper will involve the hamstrings and glutes more.
Hold your breath during the down phase and transition to the up phase. Exhaling at the wrong time, especially near the bottom position, reduces internal torso pressure and spine stability.
Keep your head aligned with your torso by looking forward throughout the exercise. Looking down contracts the abdominals, which can round your spine, making the lumbar area weak and susceptible to injury. Looking up can hyperextend your spine, which can lead to disc compression problems.
Don't pause in the bottom position. Make the transition from down phase to up phase quickly and smoothly, with no abrupt or bouncy movements that can hurt your knees.
PRIMARY MUSCLES INVOLVED
Located on the front of the thigh, the quadriceps muscle group consists of the vastus lateralis, vastus medialis, vastus intermedius and rectus femoris. Most of the mass of the vastus lateralis and medialis is close to the knee joint on either side; the muscles are commonly known as the teardrop muscles. The vastus intermedius is found mid-thigh, and the rectus femoris has action at both the knee and hip.
The gluteus maximus and hamstrings muscles are strongly involved if you squat to thigh-level or below. The gluteus maximus is the large muscle of the glutes; the hamstrings are composed of three separate muscles - the biceps femoris, semitendinosus and semimembranosus. They cross the sides of the knee before inserting on the lower leg and provide lateral stability to the knee. The erector spinae of the lower back, located on both sides of the spine, holds the normal curvature of the lumbar spine.
The quadriceps muscle group is involved in knee-joint extension in which the thigh moves away from the shin. The gluteus maximus and hamstrings are involved in hip-joint extension in which the thighs move from a parallel or below-parallel position to the vertical, bringing the pelvic girdle and torso in line with the legs. The erector spinae muscles, especially in the lumbar area, remain under isometric contraction to maintain the normal curvature of the spine.