Strength-training machines are ideal for isolating a certain muscle or muscle groups. The design of these machines position your body in such a way that only the body parts you are training move. The rest of your body remains still. This helps you conserve energy needed to effectively execute the movements in an exercise. A variety of machines specifically target the abdominals, gluteus, hamstrings and quadriceps. Some work more than one muscle group at the same time.
A leg press machine isolates the quadriceps in the thighs, but also works the gluteus muscles. Many leg press machines feature a low-lying seat and backrest, which forces you to press your legs upward on a steeper angle than leg press machines that are horizontal. A steeper angle provides more concentrated force that presses down on your body, which makes the exercise more efficient. Leg press machines normally have handlebars that help stabilize your upper body. Pulling on the handlebars when pressing up with your legs keeps you from arching your back and forces your legs to do all the work.
Abdominal Crunch Machine
The abdominal crunch machine effectively targets your full abdominal range, due to the stretch the machine creates for your body. Crunch machines have arm handles by your head and leg paddings that you wrap your legs behind. These are the resistance points on the machine that force you to pull from the top down and from the bottom up, engaging your abdominal muscles. The forward crunching movement presses your abdominals together and forces them to contract.
A hack squat machine is another version of the traditional free-weight squat, and it is safer to perform if you have knee or back problems. Hack squats target your quadriceps, hamstrings and gluteus muscles. Your body is positioned at a slight backward-leaning angle. When the safety handle is released to engage the sliding mechanism, the weight sits fully on top of your shoulders. As your body is at a slight angle and stabilized by the weight that's pushing down it, you have less chance of losing your balance and falling. Most hack squat machines feature a safety bar that catches the weight in case your legs give out.
Lying Leg Curl Machine
A lying leg curl machine isolates the hamstrings but also works your buttocks to a certain degree. The lying position is the most efficient way to target the hamstrings, because it enables you to curl your legs backward as far as you can. Most lying leg curl machines feature handles underneath the bench, which help stabilize your upper body. Pulling on the handles keeps your body against the bench and forces your hamstrings to do the work. The leg padding should be positioned above your heels and below your calve muscles to optimize the concentration of the resistance.