Today we are going to address 3 myths (or facts?) about leg training. Namely, whether leg extensions on the machine are really harmful to your knees, whether deadlifts and squats make your waist wider, and whether training with weightlifting belts weakens your core. Let's start directly with the first point:
Fact or Myth #1: Leg extensions on a machine are harmful to your knees.
There are 2 arguments that leg extensions involve a high level of stress to the knee joints.
On the one hand, there are the large so-called shear forces that act on your knee joints. When you extend your legs, the weight pulls your lower legs downward. So the force is not acting in a line to your knee joints, but at a 90° angle. This is called shear force.
And that shear force puts stress on your knee joints. The knee joints are actually much better suited to withstand compression forces than shear forces.
For example, in the leg press or in many squat variations, you experience compression forces because the force of the weight acts from the top down in a line to the knee joints, "compressing" the joints.
Second, the stress on your ACL (anterior cruciate ligament) is quite severe when you extend your leg.
You can imagine that the muscles in the front of your thigh, the quads, extend your leg and pull your shin slightly forward. However, your ACL does not like this at all, so it resists and pulls your shin back again. This puts a lot of strain on the ACL.
During more "natural" movements such as the leg press or squat, your hamstrings have a stabilizing effect on the knee joint.
They do a lot of the work of your ACL and keep your shin from being pulled too far forward by the quads.
So we have the shear forces and the greater load on the ACL during leg extension. Both represent a considerable load for your knee joint.
But this does not mean that it is BAD for your knee joint. If you expose your body to a load and this load is within the scope of your recovery capacities, then your body will adapt so that it can withstand this familiar load.
If you've never done leg extensions before and then start doing 20 sets of leg extensions a week... yeah... that's probably going to hurt your knee joints because such a severely unfamiliar load is not within your capacity to recover.
But if you've been doing 6 sets of leg extensions a week for years without your knee joints hurting, you'll most likely be able to keep doing it for a long time. Your body has adapted to this load and can withstand it.
By the way, if we look at the research, there is no evidence that leg extensions are fundamentally harmful to healthy knee joints.
So if you have healthy knee joints, leg extensions are a great addition to the leg press and squat variations for your quad workout.
In fact, with the leg press and squat variations, you have a relatively large stimulus on the quadriceps in the lower and middle part of the movement, but very little stimulus in the upper part.
Now if you use bands or chains, then you can manipulate the resistance curve so that you also have a major level of stimulation in the upper part, but that is also incredibly draining.
With leg extensions, on the other hand, you also have a large stimulus in the upper part of the movement, but leg extensions are much less fatiguing than the leg press or squat variations with bands or chains.
If you do leg extensions, it's best to do them in a higher rep range (e.g. more than 10 reps) and to do at least one warm-up set. And of course... if your knee joints hurt... use common sense and don't do the exercise!
So the fact that leg extensions on a machine are fundamentally harmful is a myth - at least as far as healthy knee joints are concerned.
Fact or Myth #2: Deadlifts and squats make your waist wider.
For most men, not to mention women, having an aesthetic body means, among other things, having a narrow waist. So it would be a pity if we put so much work into our training and then through this training we got a WIDER waist.
There are quite a few bodybuilders who warn that you shouldn't do deadlifts and squats, or not do them too often, because they supposedly make your waist wider.
Of course, in order to clarify if there is any truth to this, we first need to know what exactly they mean by a "wider waist". If the six-pack muscles (that's mainly the rectus abdominis) and the lower back get bigger, then the waist only gets wider when viewed from the side.
But that's probably not what they mean by a "wider waist." They probably mean, rather, that the waist becomes wider when viewed from the front. Which muscles widen the waist from the front view? It's mainly the obliques - that is, the abdominal muscles on the sides.
The thing is, while deadlifts and squats put a decent amount of stress on the lower back, they hardly stress the obliques at all.
Dr. Bret Contreras did some experiments and measured the activity of different muscles during certain exercises. The result was that typical abdominal exercises such as ab rollouts, crunches or leg lifts stress the obliques much more than deadlifts and squats do.
Secondly, the stress placed on the obliques during other large exercises that are also not primarily for the abs at all, such as shoulder presses, pull-ups, or hip thrusts, is just as strong as it is during deadlifts or squats.
So if you don't do deadlifts or squats because you're afraid of a wide waist, then you should not only eliminate deadlifts and squats from your plan, but also all other abdominal exercises and all other exercises where the abs (and therefore the obliques) are only secondarily trained.
The result would be that you would have to eliminate almost all exercises and from then on only perform forearm curls or similar, very small exercises!
Deadlifts and squats don't make your waist noticeably wider - certainly no wider than other typical exercises that involve the abdominal muscles do. That's a myth.
Fact or Myth #3: Wearing a weightlifting belt makes your core weaker.
If you are wearing a weightlifting belt and have mastered the proper breathing technique (namely the Valsalva maneuver - a type of press breathing - which we will go into in a separate article sometime), then by pressing your core firmly against the top of the belt, you can create a stronger intra-abdominal pressure.
This gives you stability and is very helpful during free weight exercises where your core is heavily involved, such as squats or deadlifts. This high intra-abdominal pressure will reduce the shear forces on your spine or core and you will likely be able to move more weight as a result.
Most people can lift about 5-15% more weight when wearing a belt and doing the Valsalva maneuver - but only if they are trained to do these lifts with a belt. Any of you who train with a belt know that it feels very different than training without a belt.
Because of the higher weight you can move, the load on the target muscles is usually higher as well, so your quads, for example, will be loaded more during the squat.
But what about the core? Is it more or less stressed by wearing a belt? Here we refer to a good article by Greg Nuckols, who has summarized the studies on this topic. By the way, the "core" refers to the muscles of the lower back and the abdominal muscles.
As for the lower back, it is slightly more stimulated when doing squats and deadlifts with a belt - probably due to the heavier weight that can be used.
The same applies to the abdominal muscles. The rectus abdominis (i.e. the six-pack muscles) is also stimulated slightly more when you perform squats and deadlifts with a belt. The obliques (i.e. the lateral abdominal muscles) are not stimulated more with the belt, but they are not weakened either.
So there is no evidence whatsoever that your core gets weaker when you train with a belt. So that's also a myth. In fact, it seems that it is stimulated a little more.
The only possible disadvantage you will have with the belt is that your blood pressure will go up quite a bit when you do the exercise. If you are healthy, this shouldn't be a problem at all.
However, if you already have high blood pressure, this can be quite dangerous. In this case, it is better to train without a belt and breathe evenly during the exercise instead of using the Valsalva maneuver.
If you don't have high blood pressure and you want to become more muscular and/or stronger, then you should definitely think about getting a belt, as it has only benefits for you.
But before you go out and buy a super expensive belt, it's best to first test one from a friend that fits you. This is because there are some people who do not like the constricting feeling when wearing a belt at all.
So, as you may have noticed, all of the points discussed today were myths. Of course, this could be completely different in the next "facts or myths" article!
The content of today's article briefly summarized again: Leg extensions on a machine are not harmful to healthy knees, squats and deadlifts do not widen your waist, and a belt does not weaken your core. So don't get confused if you're told something else at the gym.
If you want to record, evaluate, and optimize your training, download the Alpha Progression app here.