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#18: Leg Presses

  • Written by Denis Pedneault

201002_bodysculptingQ: Hi Denis,

What do you think of the leg-press machine? We have one in the gym and some people use it, but the trainers warn people that it can hurt the lower back. I have lower-back problems. What do you suggest?

. . . Kevin Legel

A: Hi Kevin,

Interesting question, as it’s true that a lot of people get injured while using the leg press. Those injuries, though, mostly come from improper exercise form and misuse, because the leg press is really quite safe.

Utility

The reason for using the leg press, as opposed to a standing exercise like the hack squat or Smith machine squat for example, is that you can train your legs hard without exposing the rest of your body (e.g., shoulders, vertebral system) to stressful loads (mechanical stress). I also like to use it for “active recovery” phases between hard, leg workout sessions or programs -- the leg press will be less rough on the system than regular squats. For instance, when I need to put more focus on the upper body with a client (and I will have to increase the intensity of those workouts), I have to find a way to reduce the stress on the lower body to ensure recovery and, thus, constant progress, so I trade squats or dead lifts for the leg press.

Knowing your limits

However, one thing that can be dangerous about the leg press is that you very often get the feeling that you could bear more weights – and usually end up adding more plates on the sides than you should. In that way, the leg press can indeed be a dangerous exercise (notice that I didn’t use the word “handle” when I said “bear” more weight). There’s a certain point, though, when you should be aware of your capacity (your ability to control the load) and realize that it’s time to stop piling on those plates and start relying on intensity training techniques to ensure further progress (e.g., drop sets, giant sets, etc.). The same applies to other machines like the leg curl and the leg extension. My advice is that if you can’t control the way down, stop for a count of one at the bottom and go back without cheating: it’s too heavy for you!

Correct form

Also, a lot of people don’t know how to use the leg press correctly. You might find it strange but, unlike most people, I use the leg press to work the back of the leg (on hamstrings day), not the front. If you read my last article on calf training, you already have an idea of how it works.

To work your hamstrings with the leg press, you have to understand the biomechanics of the “active extension” principle of the knee. If you know a little bit about anatomy, you know that the quadriceps is the primal agonist muscle group that extends the knee joint. What few know is that the hamstrings and the calves also extend the knee by coupled forces when used at the same time. That’s right! Since the distal part of the hamstrings inserts below the knee and the proximal part of the calves inserts above it, if you pull the two lines apart you create a vector that brings the knee backward and, thus, creates knee extension. I’ve made a drawing so that you can visualize it better. We use this principle in therapy with people who have knee problems like femoropatellar friction and need to reduce the pressure induced by the contraction of the quadriceps on the patella (kneecap). Now, to incorporate that principle in the leg press movement, you’ll have change the way you see and perform your leg-press exercise.

Active extension illustration

On the left (1) is the usual line of pull of the anterior chain (quadriceps). On the right (2) are the combined forces of (A) the hamstrings and (B) the gastrocnemius (calf muscle) that form a new vector (C) that will close the posterior chain of the knee, thus pulling it backward.

Correct positioning

1) Feet should be about hips wide. Forget that stupid thing about feet having to be about shoulders wide: there’s absolutely no relation at all between your shoulders and your feet – end of story!

2) The weight and push force should remain under your heels at all times. Try to focus on your heels, because if you’re like most people and you don’t pay attention to your heels, you will push with your toes as you press up, which changes everything.

3) If there’s extra padding for the head and you can take it out, do so. I don’t want to get into too much detail here, but everything that pushes the head forward alters posture and, thus, your positioning and stability (I explained that in my article on the bench press). Your head should remain at the same level as the rest of your body, and that applies to a lot of exercises.

4) Your hips, and not your back, should be your main support on the bottom of the bench. Your lower back shouldn’t touch the bench, and you should even have enough space to be able to put your hand behind your back. That positioning ensures the anteversion (forward tilt) of the hips, which will have the effect of stretching the hamstrings. If you’re correctly positioned, you should actually feel a direct stretch right at the top of the movement when the knees are extended and the weight is on the heels.

5) The knee should be in complete extension at the top. This is another false statement you hear a lot: don’t bring your joints to full extension! When you train, you already put your body under a lot of mechanical stress. Using functional range of motion on your exercises preserves the integrity of your musculoskeletal system and keeps your joints and other components healthy. In fact, not doing so is the main reason people injure themselves and develop chronic problems like arthritis and tendinitis through training.

Leg press illustration

Correct form: head in line with body, hips tilted and supporting the weight, functionnal ROM at the hips, and feet firmly on the board about hip width with heels as the point of pressure.

So, to sum up the correct starting position: your head is flat on the bench; your hips are tilted forward so that your lower back doesn’t rest on the bench; your knees are in complete extension; and, even if your feet are flat on the plate (about hips wide), you hold the weight on your heels. Now you’re ready to do one rep . . .

Correct form and common mistakes

Start by slowly controlling the weight on the way down and focus on maintaining the load on the heels. You go as low as possible without letting your heels or hips leave their point of support. If done correctly, you will realize that not only will you not go as low as usual but you will feel the back of the legs working more than the quads. As the critical point is reached, there should still be a lot of space between your belly and your thighs. The functional ROM (range of motion) of the hip in flexion is about 120 degrees at best when the knee is also in flexion. Passing that point, your body will compensate with other joints (e.g., the back) to do the movement, and that’s even truer if you’re supporting a load on top of everything else!

Pause at the low position for one second to further involve the hamstrings and then slowly push the weight back using the heels until your knees reach full extension. Remember what I said: Your body adapts to everything it’s exposed to, so by restricting your range of motion in your movements, you lose your “functional” ROM and, as a result, you’ll end up overstretching your tissues when you accidentally exceed your “actual” ROM. That’s why you see so many trainees complaining about elbow, shoulder and knee problems. On the other hand, there is a difference between bringing the joint to full extension (and preserving structural integrity) and exceeding into hyperextension and pushing the joint to the limit. Some even don’t bother controlling the movement and end it with a quick “jerk.” Ouch!.

Remember to keep your head on the board while pressing. I’m stressing this point because you will feel the tendency to push your head forward, which changes the biomechanics of your posture and, thus, the stability of your support base. If you’re using heavy loads, you want to maintain the strongest position possible if you want to avoid injuries. Again, remember to push with your heels and not your toes. Switching from the heels to the toes will transfer the stress to the anterior chain and will recruit the quadriceps to do the movement. That’s why you’ll feel some pain in the knee if you have any patellar problems, and, again, the same applies to other compound exercises like lunges and squats.

One other way people injure themselves in the leg press is trying to go as low as possible (thinking it’s better), which will have them roll their hips as they go down. When that happens, the load that was easily supported by the hips (a very strong and stable joint) is switched to the lower back (a mobile and vulnerable area). That’s how people end up with hernias and pinched nerves, and is why I emphasized to tilt your hips so that they become your main support.

Leg press illustration

Common mistakes: forward push of the head, letting the hips roll off the bench and using the lower back as support, not respecting functional ROM (i.e., bringing the thighs to the body), and using the front of the foot (toes) as the point of pressure.

So, to sum up the common mistakes: not keeping the head on the board at the same level as the rest of your body; letting your heels lift off the plate or your hips roll off the bench; bringing the thighs too close to the body; and hyperextending the knee at the end of the movement.

As you can see, training properly, even on a machine, is more complex than just sitting on it and lifting or pushing plates. Remember that you are in that apparatus with a goal: increased muscle development, and that it can only be achieved through discipline and safety.

Have a great workout!

Sincerely,

. . . Denis Pedneault, Canadian Champion 2005, 2006 and 2009

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