Shear Nonsense: Debunking the claim that Leg Extensions “shear” the knee
ฝัง
- เผยแพร่เมื่อ 22 ส.ค. 2024
- Watch our free masterclass Compound vs Isolation:
online.smarttr...
In this episode of Brignole Muscle Mechanics, we examine the factors that determine whether or not “knee shearing” actually occurs when using a Leg Extension machine.
I've never been in such good shape without any injuries since finding the information Doug has been putting out. Thank you 👍
Shearing is a force, Doug -- not a motion. Conflating motion in an unrestrained model with one of *many* forces that would be occurring in an intact, physiologic condition is a great way to confuse yourself and others.
It is true that shearing force isn't something we should inherently fear (in a leg extension or in any other exercise), but it is NOT because shear doesn't exist in this exercise. If you've ever drawn a free-body diagram or studied how forces summate, this should become fairly obvious. There is absolutely shearing force being created throughout a leg extension; the question is simply about two major things:
1) how much and what other forces are present at the same time which would then dictate the net forces and associated torques on the entire segment (which determine whether the segment will rotate about the axis in question -- the lower leg about the center of rotation of the knee in this case)
2) the tolerances of tissues *within* the segment for various internal stresses that might occur as a result of the exercise. Just because stuff isn't moving doesn't mean that there isn't some amount of microtrauma or some amount of small-scale tissue deformation. In fact, deformation is always occurring to some degree; it just isn't always a concern. It depends.
The irony here is that a portion of this representation is actually (more or less) backwards from what's really occurring. As the knee extensors work to oppose the external torques, we can see a change in the tendency for those muscles to create a "net anterior shear" of the tibia as we change where we apply the external force -- typically via a pad on the input arm if we're talking about a knee extension on a modern machine. As we move the point of external force application closer to the knee joint, we're reducing the moment arm for that external force, thereby meaning that the amount of internal force required by the knee extensors (which *do not* experience a moment arm change) to oppose that torque will also go down. What this ends up looking like is a reduced anterior shearing force coming from the knee extensors while the posterior shearing force from the external force remains the same. The result is less difference between those two shearing forces, meaning less reliance on additional passive structures (e.g. knee ligaments, joint capsule, etc.) or active structures (other muscles that co-contract to compress the joint and/or provide additional posterior shearing force) to keep the tibia from dislocating forwards.
Alternatively, if the internal muscle force is kept the same, then the external force must be increased as its point of application moves closer to the knee (up the tibia), resulting in the same basic situation: more closely matched shearing forces that then result in less need for other tissues/structures to "pick up the slack" and keep the joint stable.
"It would be suggesting that ALL exercises create a shearing force on ALL joints any time you apply a perpendicular force."
Umm... yeah. That's pretty much the case. And that's why we shouldn't fear any particular force like shear; it's always present to some degree. This video suggests that something is absurd when that's exactly what's actually happening.
Inb4 someone thinks I'm attacking Doug by trying to provide this clarification.
I'm replying to clarify something:
Shear and shearing *in the context of this video* should be relegated to describing force, lest we cause more confusion than we solve. The issue that is typically brought up when talking about knee extensions is one of shear as a harmful force (assuming the people talking about it understand it at all).
@@JudoGeoff So Leg Extensions are completely safe to do? Or do you have any concerns with them? Don't do them too often, don't go too heavy, stay in the high 10-20 rep range etc?
I have trained in several gyms. Met men who blew out a disk with squats, or tore a tendon. Never met anyone hurt from leg extensions.
research your knee ligaments, the MCL and LCL do not cross the knee joint in the frontal plane, only ACL and PCL do this front to back. Using a hinge is also a poor example for describing a synovial joint that is designed to roll and glide. Comparing the elbow to the knee is comparing two different types of lever systems (elbow is class 1 and knee extension is class 2). lastly, the shearing occurs because two opposing forces are being applied to the lower leg at opposing ends. this encourages rotation anterior at the tibial plateau, and posterior at the malioli, thus the tibial plateau glides forward without the appropriate roll, aka shear. Effect of this on individuals with no ligament laxity is negligible but we have anti-shear attachments for isokinetic rehab machines when putting post op ACL patients on there for a reason. had students forget to put on the attachment and have the patient blow out their knee again.
The fact that this is an open kinetic chain movement (not weight bearing) means there is no co-contraction of the hamstrings pulling back on the tibial plateau. this fails to provide force closure to the joint to maximize joint congruency.
Your personal experiences are anecdotal evidence of resistance to articular cartilage wear, and do not infer a different interpretation of the biomechanics "because my knees feel fine"
T-nation does a good job demistifying the subject
www.t-nation.com/training/why-your-knees-perform-like-aging-water-fowl
Neil, do exercises such as Cable Squats cause more knee shearing than regular Barbell Squats?
@@CalebRox depends on how they are performed... A front squat requires more forward knee travel which puts larger shear forces on the knee, but in a healthy knee with proper technique this difference is negligible. The front facing cable squat changes the angle of the force to front load the quads. This can put the knee through additional shear, but if the knees are healthy and load is built up over time this should be fine. This exercise is difficult to do heavy anyway as you would need to lean back more and more. This puts the line of force more in line with a traditional squat.
This is outdated stuff
I would urge anyone who has not already done so - BUY DOUG'S BOOK !
I did Brignole Squats for the first time yesterday, and I can tell you they are no easy option. Today I have DOMS like you wouldn't believe, and zero lower back pain. 👍
Are you referring to the cable squats? Or sissy squats?
More great information and explanation from Doug, I bought his book last July and have been lifting weights on and off since the 70's but have made more progress with less injuries now that I have followed many of the ideas and exercises he outlined in his book. Thank you Doug for giving back to the fitness world .
I enjoy Mr Brignole’s explanations very much.
I've been training for 40 years doing most of the traditional leg training exercises. Heavy leg extensions, hacks, squats etc. I have no knee pain at all; just thick legsThose who claim the leg extension cause shearing or damage to the knee are wrong. At least when it comes to me & my genetics. Thanks Doug.
Leg extensions done incorrectly will damage the knees.
@@rockon8174 sure, but anything done incorrectly can potentially damage whatever is involved. This isn't news.
Lets hope Athleanx takes note of this video.
Too famous to change beliefs now.
@Panzer Track BroleanX
Rather he should take notes from Athlean X. This video proves nothing
@@dia_dad_on_a_bike you mean notes on how to use fake weights ?
Doug, why no mention of the knee cap (patella)? That's what gets damaged. From a Google search "The problem with the leg extension is twofold: The leg extension places maximum force on the back of the patella ("knee cap"), the thinnest portion of the cartilage. This can lead to cartilage damage. When you squat, the thickest part of the cartilage is loaded during the squat's maximum force." I used to love leg extensions, but now if I do them regularly, I get MCL pain in my left knee. When I lay off, the pain goes away. There is a connection.
I asked a question about this not too long ago as well and it was ignored. I feel that Doug doesn't want to address any problems with the exercises he recommends, he's happy and quick to tell people to stop doing compounds though.
Great video. On leg extensions I always make sure the weight is heaviest to start with and lightest at the top extension of the exercise. Save a lot of strain on the knees. I think of the leg extension as if you are doing a tricep extension. Heaviest at the beginning of the exercise and lighter towards the end.
Have you seen a leg extension machine which has no cable? There's just a rod between your feet where you put the plates. In this case, the weight becomes a downward force parallel with your lower leg in starting position. In this type of set up, the hardest part is when you are towards the end of the rep.
When I saw athlean x video on this I was surprised because all through my twenties I did those as a finishing exercise each time I did my leg workout and I used as much weight as I could push which was quite a bit and I never had any problems.
I've had more issues with squats that I have with leg extensions for my knees and I don't have much have any issues with squats but I feel it more in the knees that I did with leg extensions.
Love you book and great video. I think what most people feel when they do this exercise is the shear overtraining. And not giving their body parts enough recovery time. And I also believe that too many people Eagle lift. They forget what bodybuilding is really about
Good videos and much better sound quality. Also nice pun in the title, though I am confused about the spellings ;)
IMO, the only! differences between (SQ) squat and (LX) leg extension are in that the spine is not being compressed (in LX), the glutes (and others) are also working (SQ), the lever is longer (LX) and the max force on the quads is when the knee joint is bent (90degrees in SQ) as opposed to straightened (180degrees in LX). Because the lever is longer in LX you can go with a lot less weight and strain on the joints while achieving higher loading of the target.
Some may like squats more because they really save time: loading many muscle groups at once (though not optimally and with more joint and bone stress).
Also I think what is meant by the "shearing effect of leg extensions" is that unlike many other exercises (bicep curls, skull-crushers for triceps, squats, etc.) the MAX force and resistance here is applied when the joint is 180 and not 90 or less (where it is thought heads of the two bones involved can support each other against shearing forces). Though I understand your point about the quads applying a big compressive force (almost "20 times" the weight used) to keep the two bones as a single unit and bone, we have to admit that it is a vulnerable position. But I mostly agree with the points you make.
I couldn't agree more with you. I have been doing leg extensions my entire life and have had all of my clients doing leg extensions. Done with proper form will not hurt the knees at all
Great stuff as always Doug. But, in my experience, this is one that most just don't get. Regardless of a logical, quantifiable explanation, most just don't want to hear it. To them, the Squat is their primary Quad exercise and leg extensions are either 'evil', or, they are just something they throw in at the end as a "shaping" exercise! They just don't get it.
David Speakman Haha ! You’re right. Many people (most people) aren’t able to grasp the logic.
Leg extensions done incorrectly will stress the patella tendon. So, yes, one needs to execute a leg extension with care too.
Great explenation 👍
Waiting for the shoulder/rotator cuff ....
I often wondered where that idea of shearing the knee on a leg extension came from. Side by side with the skull crusher picture instantly de bunked it for me.
Great content master, really u debunks all myths.
Nice explanation! Thanks. Back to leg extensions for me then
Thank you for the video Doug.
Almost 1,000 subs Doug!
Keep it up, and continue to promote your channel on other media like bodybuilding reddit subs!
Once again, well demonstrated!
For 50+ years leg extensions were my go to exercise for knee healing when I needed healing. Light weights, high reps, high frequency. Today in my older years I have pain with LE's.
Thank u Doug! I love yours explanation 🙏
These are some solid hot takes
Great Info as always !
Some leg extension machines do not have cables, there's just a rod between your feet where you put the plates. In this case it's a totally different scenario, the weight now is a downward force parallel to your lower leg in starting position. I hope you could clarify on this one.
Very convincing presentation in support of leg extensions and their lack of association with shearing forces, but if not shearing force, then is there a risk to the patellar tendons in performing the exercise? Due to the efficiency of the exercise in targeting the quads and the fixed position of the thigh on the machine, the patellar tendons would seem to receive a lot of force in executing the movement. Any reason for concern regarding the patellar tendons?
John Taylor There’s no reason to believe that the patella tendon would be strained any more during Leg Extension, than by any other exercise that loads the quads. In other words, the more load on the quads, the more load on the patella tendon. The more efficient an exercise is (i.e., the perpendicular the resistance is against the lower leg), the less weight that needs to be used, because a higher percentage of that load is loading the quadriceps.
Good video and I like your opinion, but the thing I think you are missing is that your patella is the thing that is "sheared" on the femur when you do leg extensions. I have two knee replacements, so I do limited range leg extensions (just the last 30 degrees), with emphasis on form and contraction. Most people use way too much weight with lousy form (momentum swing). This is what hurts knees. Look at Scooby1961's video on this topic. I think he explains it better, but I still like your stuff.
At 8:43, I don't get it why you use the angle between the lower leg and the downward weight, this makes the heel the pivot of work being done when in fact, the knee is actually the pivot in both scenario. You also forgot to notice that in squats, the UPPER LEG is the working lever since the lower leg is almost stationary and the load is within the upper thigh compared to leg extension where the upper leg is stationary and the working lever is the LOWER LEG since the load is within the ankles. Angle of ROM should have been measured between the thigh and the vertical which is at least 90 degrees since the knee is the pivot. Squats take more load because, as seen in the left picture, the load (green arrow) is much nearer to the pivot (knee) so there's less work done compared when the load is in the ankle which is farther from the knee. This is proven when doing squats and you get fatigued going to your last rep, your body naturally leans forward shifting the load (green arrow) even closer to the pivot which makes it less work compared to early reps.
What needs to be taken into account is the direction of the driving force that is being produced by the person who is doing the squatting. Since balance must be maintained (i.e., keeping oneself from falling forward or backward), the driving force is "straight down" -- directly opposite gravity. This driving force is being applied mostly "through" the length of the lower leg -- mostly parallel to it, rather than perpendicular to the lower leg. Imagine trying to unscrew a very tight bolt, using a crescent wrench. If you applied the force on the wrench mostly parallel to the handle (i.e., in a direction that is mostly toward the nut), rather than perpendicular to the handle, it would require significantly more force. But, given that the force required to unscrew the nut is the same either way, it would be most efficient to use a force (on the crescent wrench handle) that is mostly perpendicular to it. The same is true with regard to squats (or any mechanical endeavor that involves a lever). Whether you load your quadriceps with X amount of force by using a lever (i.e., lower leg lever) that allows 100% of the weight being used, or 5 times X using a lever (i.e., lower leg lever) that only allows 20% of the weigh being used, the quadriceps is loaded the same. Why load the spine with 5 times more compression than is necessary? In terms of the squats being a compound exercise, this too has "pros" and "cons". Given that more muscles are involved (as compared to isolated exercise), there is a significantly higher cardiovascular demand -- even if there isn't more actual loading of the each muscle involved, than would occur with isolation exercises. There is -- however -- a neurological "conflict of interest" which occurs when doing squats. Since the hamstrings is BOTH a knee flexor, and also a hip extensor, the hip extension involved during squats activates the hamstrings (in addition to the glutes and adductors). The hamstrings are the antagonist to the quadriceps -- meaning that they each bend the knee in opposite directions (the quadriceps extends the knee, and the hamstrings flexes the knee). Thus, activation / loading of the hamstrings compromises the ability of the quadriceps to fully engage, as per the rule of "reciprocal innervation" (two opposing muscles cannot fully engage, with full force, at the same time). For example, when your biceps brachii is loaded / activated -- while doing some type of "curls" -- the central nervous system sends a "relaxation synapse" to the triceps, which prevents it from contracting. This the body's way of preventing "interference" (self defeating efforts). The same thing occurs in the lower body. In addition to the hamstrings / quadriceps conflict, there is also the reciprocal innervation that is triggered as a result of the rectus femoris (the only one of the four quadriceps muscles crosses the hip joint) and the glutes. The rectus femoris assists in hip flexion, which the opposite of hip extension, that the glutes are trying to produce.
I think you misunderstood me sir. In free weights (without any cable or machine ) load is always straight down due to gravity, that is a fact. Force is greatest when it is perpendicular to the working lever (just like in your wrench example), I also agree on that one, that is physics. But it is also according to physics that in order for 'work' to be done there has to be movement. So if, like you said, "driving force is applied through the lower leg" there will be NO WORK done since the lower leg is almost NOT MOVING (it moves a little just to help you body balance the weight, in sissy squat it does move at all). Same with the ground you are standing on, it applies an equal force parallel to the weight but it does not do any work. Work is being done with your upper leg functioning as the working lever. Proof of this is that, since force (load) is greatest when it is perpendicular to the working lever , squat becomes harder as you get lower. Hardest when you upper leg is parallel to the ground and perpendicular to the downward force from the load. Easiest when standing, upper leg is vertical position and parallel with downward force from the load. Other than that, I completely agree with you sir that it's not wise to load your skeletal system with so much weight so isolated exercises are best when maximizing your gains.
@@Snap_FL -- I understand what you’re saying, and I appreciate your effort to intelligently analyze the mechanics of the squat. These things can be very mind-bending sometimes. Allow me to add a bit more information to the analysis.
A joint movement (e.g., elbow bending / knee bending) can occur by way of several different means - i.e., by several different muscle contractions, and also passively or actively. For example, consider a “One Arm Dumbbell Row”.
During a One Arm Dumbbell Row, the elbow moves from being straight (in the descended position), to being bent (in the ascended position) - exactly as it does during a biceps curl, or during a triceps extension. However, this elbow-angle change is not being produced by the biceps, nor by the triceps, during a One Arm Dumbbell Row.
During a One Arm Dumbbell Row, the forearm simply hangs (vertically) from the elbow - passively (no different than a rope, attached to your elbow…if you had no forearm). The elbow bends by default, because the distal end of the humerus (the upper arm bone) pulls upward on the upper end of the forearm. As long as the forearm is allowed to hang vertically (no tilt in either direction), there is essentially no participation by the biceps or triceps. Yet, a similar type of elbow bending occurs during biceps exercises, as well as during triceps exercises. The difference between these three scenarios is the direction of force being produced by the person, and the different directions of resistance.
The same applies during various type of “knee extension”. For example, when we do Hanging Leg Raises (with bent knees), our legs start by handing straight down - with the knees “extended” (straight). We pull our knees upward - simultaneously “flexing” (bending) the knees. Then, we again bring them down - simultaneously “extending” (straightening) the knees. This does not require much (if any) quadriceps force - nor hamstrings force - even though the knees are moving in a way that is similar to Leg Extensions and Leg Curls.
Let us now apply this concept to squats.
When we perform a barbell squat (or any other type of “free” squat), the knees move from a “flexed” (bent) position, in the descended position - to an “extended” (straight) position, in the ascended position, but mostly (about 80%) as a result of the hips being pushed up and over the feet and knees.
This upward rise of the hips and torso is produced mostly by the downward push of the femurs, which is caused by the hip extensor muscles. As we push downward against the ground (mostly “through” the length of the lower leg, rather than “across” it), the ground “pushes back” with an equal amount of “ground reaction force”. If we were to place a scale UNDER our feet, when we’re squatting, it would read an amount that is equivalent to our body weight, plus the weight we have added to our body (usually by way of a barbell on our shoulders).
Now, compare the above scenario to a type of squat that is performed on a “sissy squat bench” (explained in one of my other TH-cam videos). In that situation, the sissy squat bench places a brace behind the upper part of our lower leg, on the posterior side. This creates a pivot there, which causes the ankle to push forward against the padded brace in front of it. This scenario loads the quadriceps (exclusively), as evidenced by the fact that a scale placed UNDER the feet would read “zero” (when in the descended position). The force of your thrust would shift entirely against the front of your ankle.
This change in the direction of force (from the bottoms of your feet to the front of your ankles), occurs without there being any change in vertical position of your lower leg - as you’ve described in your message. But there is a big difference between a downward thrust (against the bottoms of your feet) and a forward thrust of the lower leg / ankle - even though both movements look similar.
In other words, in order for a significant amount (percentage-wise) of the force that you produce, to load the quadriceps, there MUST be a significant amount of forward ankle force - even if the lower leg stays still. The reason for this is one of Newton’s Laws which states, “For every action, there is an equal and opposite reaction”.
Imagine being in the descended position of a barbell squat, and then forcefully extended your knees -- without any hip extension force. This would produce a forward thrust by your lower leg, such that your feet would slide forward inside your shoes, and - if the floor did not provide sufficient traction - your feet would likely slide forward as well. Knee extension that is caused MOSTLY by quadriceps force, will automatically cause the feet / ankle / lower leg to push forward (in a direction that is perpendicular to the lower leg) - whether or not the lower leg changes it’s angle. A significant quadriceps force (forceful knee extension), in which the lower leg is held still, would cause the upper end of the femur to rise, and would produce a forward force by the lower leg, such that you would feel your feet pushing toward the toes (not toward the heels or the bottoms of the feet), or the front of your ankle would push against a brace that prevents the ankle from moving forward ("equal and opposite reaction").
This is why squats require much less quadriceps force, than gluteus force. As coordinated humans, we sense how much force we need to use with each muscle (quadriceps versus gluteus), without even thinking about it. A robot, however, would push itself backward (off balance), if it was programmed to produce significantly more “knee extension” force, than “hip extension” force.
When we do standard sissy squats (where you lean back, and make the femur more vertical), we shift more force to the quadriceps because we cause our lower leg to be more horizontal. Thus, as we push “forward” with our lower leg, against the balls of the feet (toward the toes), we do so with a lower leg that interacts more perpendicularly with gravity. Thus, the hips rise upward by virtue of knee extension (quadriceps contraction), rather than by virtue of hip extension (gluteus contraction).
Check out my “sissy squat bench” video, and you’ll have a better grasp of the mechanical difference between these two different directions of thrust.
Cool gadgets and an excellent video
It's not the sheer force that you have to be concerned about. It's the cartilage on the underside of the knee cap that you have to worry about with this exercise. This exercise can lead to softening or breakdown of the cartilage, this is called Chondromalacia. This breakdown or softening of the cartilage can lead into osteoarthritis. If and when this does happen the body has no way of repairing this damaged cartilage.
Still safe
The kickback is the second most effective triceps exercise and not far behind diamond push-ups, coming in at about 88% of muscle activation. By bending forward, you really have to work against gravity to move the weight up and down. Cables will create constant tension do them both.
Great explanation... makes so much sense,,, about time,had scientific evidence, instead of old school thinking..
Well explained. Can you make a video on Bent over rows and the angle of torso that should be used. Thanks ✌🏋
Buy his book, which among other things clearly defines the pros and cons of the row.
Another great video, Doug! Over the years I did leg extensions with multiple brands of equipment. When I go really heavy, 80-90% of these machines result in some form of knee pain. So my question is, which mechanics makes a good leg press machine?
Virt Real The vast majority of Leg Extension machines are not built correctly. They don’t shear the knee, but they (often, unfortunately) fail to allow the knee to move in the most natural way, at least to a small degree. Sissy Squats are good, although there are various versions and all have some pros and cons as well. Standard 45 Degree Leg Presses have more cons (negatives) than pros (advantages), and this will be the next topic I’ll discuss.
Thanks for sharing your view on this, Doug. I remember this old, chain driven leg extension which worked great, but I forgot the brand. My current gym has the latest Nautilus version, which isn't bad but it's not 100% pain free. I saw a Freemotion version in a video that caught my attention. You simply put your foot in a 'sandal' which is attached to a cable, brilliant! Would love to try that one. Anyway, I'm looking forward for your next video!
Virt Real That sounds great, because the knee is free to extend any way IT wants to, and isn’t forced to travel the trajectory dictated by the machine’s unidirectional pivot.
@@dpbrig1 Is there a leg extension machine you can recommend?
I always got very good results from leg extensions, so I was surprised how negatively it has been portrayed by many.
The majority of ppl spewing this leg extensions are bad nonsense watch a few athlean x videos and take it for gospel as if Jeff is never wrong
Mr. Brignole, what's opinion on Bulgarian Split Squats? Also, my orthopedic says I have hereditary Chondropathy of the patella... What leg exercises would you have someone like me do or avoid?
I think the problem with the leg extensions is that it is an unusual exercice for the body: it makes the quads contract without making the tibial hamstrings contract. Outside of the gym, all the positions that need the quads to produce strength also activate the hamstring. The hamstrings play a role in stabilizing the knees, without them contracted while doing leg extensions some knee pains may appear.
Feel free to comment if you have anything to add about this.
My point to add would be that this ignores 1) the existence of tasks like kicking in sport, self defense, etc. that produce forceful knee extension without the need for as much concentric knee flexor involvement, and 2) contexts in the upper extremity where similar tasks are performed, too, and for whatever reason, people don't seem to be bothered by doing "isolated" elbow extensor work. I find this interesting.
It also presumes that a knee extension exercise necessarily involves no activity of the hamstrings, and I'm not convinced that that is actually the case (at least for everyone).
@@JudoGeoff comparing the knee extension with the elbow extension is not relevant as the structure of the joint is totally different, and the way they are used too.
The better an exercise isolate a muscle the better the muscle works. There is a limitation in signals sent from our brain to our muscles to avoid two antagonist muscles to contract hardly. It is a reason why isolation exercises are very efficient: the purpose is to contract only one muscle, so the antagonist muscle doesn't interact during the movement.
I have always used extensions only as a light warmup. Two days ago did 5 sets pretty hard, with good form. Knees still sore. Do not really want to try again.
60zeller As I stated in a separate response, most Leg Extension machines are built incorrectly. The left and right knee each have a different angle of axis. Forcing both knees to extend straight, as if they both share a parallel axis, is stressful to the knees. How stressful depends on how far laterally your toes point. If your feet point straight forward, than your knees are closer to that parallel axis. If your feet point outward significantly, your knee axis are more distinctly different and would have more difficulty with a standard leg extension machine.
Thanks Doug! 👍👍💪💪
Which of the 2 is better for Cardiovascular health?
George K There is no doubt that squats produce a much greater cardiovascular demand. But if the objective is optimal development of the quads, with the least skeletal abuse, Leg Extensions are a better choice. You can achieve cardiovascular stimulation in other ways.
George K No, that’s not correct. The formula (simplified) for calculating muscle load is as follows: The load (weight used, plus body weight, if appropriate) divided by 2 (limbs) X the length of the operating lever (a ratio, as per lever mechanics) X the percentage that corresponds to the angle of the lever, relative to the direction of resistance.
So, a 300 pound squat, divided by 2 (legs), X 20 (approximately), X 30%.
@@gtm5650 Approximately 1,215 pounds of load per quadriceps (180 + 225 = 405 x 20 = 8,100 x 0.3 = 2,430 divided by 2 (legs) = 1,215 pounds)
@@dpbrig1
Wow! Which physics formula is this?
Does this contradict the Knees Before Toes guy?
Doug Brignole is slowly debunking every myth and misinformation that have been spread around the bodybuilding circuit for Decades. I just completed 12 months using the BRIG 20 and have never been in better shape at 55 with joint health intact. I advocated his principles to students in Taiwan in 2020 and even though I've been a personal trainer and wrestling coach for 35 years his concept to resistance training is a revelation.
Watched your video on sissy squats and this one. During leg exertions, the quads are loaded when the leg is straight - with the force applied near the foot. During sissy squats (on apparatus), the quads are loaded when the knee is bent - with the force applied near the hips. It seems to me there is a greater potential for knee damage in one of these exercises in comparison to the other. Which configuration and load is the knee designed to handle? Seems to me the leg extension is an unnatural situation for the knee.
888bam There no “risk”, per se, in providing resistance to the quadriceps / knee at the end of the range of motion. However, it is a little bit risky to fully lock (straighten) the knee, against resistance. This is because of an issue called “screw home”, which refers to a slight rotation of the lower leg. This occurs because the condyles of the femur and of the lower leg must shift in order to “seat”. This could, eventually, theoretically, cause wear on the condyles. The solution is simple - avoid the final 5 degrees to 10 degrees of the ROM. Having said that, there is an advantage to the quadriceps in providing resistance through the entire range of motion, as compared with providing it only, or mainly, in the early part of the range of motion.
Doug Brignole Thanks for the quick reply. So with the sissy squat, there is no risk of wear on the condyles, correct? This is of special interest to me because I have a meniscus tear on my right knee.
888bam A meniscus tear is not related to the issue of the condyles. However, there is a risk for anyone with a meniscus tear, simply in heavily loading the quadriceps. The meniscus is under the patella. The quadriceps / patella tendon runs over the patella. Therefore, the more you load the quadriceps, the more downward pressure that is placed on the patella. This could exacerbate a meniscus tear. Your issue is less related to which exercise is “less natural” to knee extension, than it is to how heavy a load you use. The more load you place on the quadriceps, the more pressure you place on the meniscus. Unfortunately, you’re better off avoiding the use of any resistance that prevents you from getting fewer than 20 (or 30) reps. Your can still grow with high reps, but you’ll have to use muscle fatigue for growth, rather than overload.
Doug Brignole Thanks for the advice - very helpful!
Doug, would you say that the lower you place the load on the leg the better? The extension machine I use , I normally anchor it near the ankle but I can change the position to anchor it on the top of the foot.
Would you recommend placing the load on the top of the foot, or is the ankle fine?
Lee Tuck The ankle is fine.
At last sanity on this subject. I work in PT and use Leg Extension for knee rehab and VMO activation.
Hi. Very interesting stuff and good explanations. Do you have info in your book on how to train to prevent n disc bulge or herniation
Truth! Thank you!!!
I am sure it wouldn't hurt to lighten your load regardless. You can hurt yourself with a big ego on any exercise. Many people are saying this exercise IS safe, if you keep proper form and don't overdo the weight.
Usain bolt, the fastest man ever, does legs extensions.
I wonder why physical therapist's don't recommend it
Sir if u do leg extensions with 100 pounds and I do squats with 100 lbs. Your legs will still be nothing
What about lats???
This video is great, but it's going to hurt alot of feelings.
Which is no bad thing to be fair.
5:40 - Your example is nonsense. If you now apply load on that ankle, and you try to extend your leg, so you are actively pushing against the load, you will definitely create a shearing force on the joint. You tried to show us that there is no shearing force on the way down. But there definitely is on the way up.
Also info about perpendicular and compression force seems like nonsense to me. It's not about force in general. On squats the load is perpendicular, you are right, but parallel to the axis of tibia, compared to leg extension, where it's perpendicular to the axis of tibia, which heightens the stress on ACL. And that's the problem, not perpendicular force by itself. But that's just my opinion guys, believe what you want
🍺
Doug, you can also make a video about isolation exercises, because many people keep saying, that compounding exercises are much better, than isolating exercises. Like here for example th-cam.com/video/TBxivHNGWbA/w-d-xo.html
Okay…hats off to Doug and his clearly demonstrated ability to sculpt his body. That said, he got very little right in his explanation, drawings (arrows often reversed, or in the wrong place or missing their opposite vector at the other end). In short, this is neither the explanation of a mathematician nor a physicist. It looks scientific, and looks mathematically correct, but it is not. Don’t believe a words of it. He is saying a bunch of things that support his (pre-existing/biased) opinion, and then showing things that don’t support same. It’s like showing a bunch of pictures that are incomplete or just don’t demonstrate a flat Earth, while a voice-over confidently and authoritatively proclaims those pictures PROVE a flat-Earth. Sorry, but this video shows a very competent athlete getting way out of his depth in basic Statics/physics.
Hi Doug... I'm just wondering how you got on with your Covid vaccine challenge?