Understanding Forces
The reference to force in this article will focus on force that isn’t a byproduct of strength coupled with acceleration but rather how forces are placed upon the body during certain exercises. As we know, training can be very beneficial to anyone’s fitness or athletic goals, but understanding some of the ways in which these exercises negatively affect the body can aid in decision making in programming as well as make it easier for us as professionals to accommodate athletes and work around certain injuries.
Sheer Forces
The easiest analogy I can think of to describe sheer force is to think about whittling a piece of wood. In essence, you’re sheering off the top layer of the object in an angular motion. There are certain exercises that may or may not be a part of your program that create these sheer forces. If these exercises are performed correctly, we can minimize the negative effects of these forces or keep them under control.
The following are some popular exercises that produce sheer forces:
Good mornings: Think about the way this exercise fires up your erectors and low back. This exercise is a staple in nearly every competitive powerlifter’s training program and may be a necessary evil to accomplish a good power squat total. Things to keep in mind—if the athlete has a predisposition to low back injury (heredity, previous injury, anterior pelvic tilt) or if you’re using this exercise to create strength in the lumbar erectors and hamstrings, it is by no means a terrible exercise. It’s just a little more risky than other exercises.
To make adjustments to this exercise, try a Romanian deadlift. It’s almost the same movement biomechanically, and in most instances, it allows for a greater load and cuts the sheer forces down drastically. Still having problems? Try the two for one approach. Hit the hamstring curl hard, focusing on the eccentric part of the rep, and you will get more actual hamstring stimulation, according to the EMG, and hardly any sheer force on the back. We can then couple the curls with a low back variation, 45-degree hypers, prone Supermans, glute ham back extensions, or even glute hams. Your body is at a much more disadvantaged position, and the load will never be as high as in an Romanian deadlift or good morning. Load isn’t always everything (it sounds foreign to even say that). The most important aspects are muscle overloading, overcoming stress, working the muscle maximally, and adapting the muscles. I can train my posterior chain extremely hard by holding a 45-lb plate on a glute ham machine and be fried.
Leg extension: Just like the good morning, the load is placed in relation to the center point of my lever (knee joint) and dictates a high level of sheer force. This is a very popular exercise and is a great one. We just have to be careful of those injuries and predispositions before throwing these exercises into our programs. For example, post ACL surgery or acute ACL injuries are probably not good candidates for this exercise. The leg extension actually places more sheer force on the ACL than a squat. Also, this exercise places more sheer force on the patellar tendon than a parallel squat.
This exercise targets the VMO arguably better than any other exercise (huge in promoting knee stability), so any adjustments are a bit of a downgrade if this is why you’re doing this exercise. A good leg press hits the VMO because a good leg press should be accommodating resistance. Pushing a sled from the backpedal position will smoke you out. With the leg extension, I prefer to keep the volume fairly low at 1–2 max sets of 8–10.
Compressive Forces
Think of stepping on a tomato. Obviously, the first exercise that comes to mind is the squat (which I love). The squat is viewed as the king of all exercises, mostly because you can hit every muscle under the bar in the squat, directly or indirectly, and it elicits the highest GH response due to the axial loading. Axial loading comes from any load that puts pressure vertically over the spine, femur, tibia, and on down.
I know most of us probably can’t think of a weekly training regimen without the squat in there at least once or twice, but sometimes you have to adjust. Think of it this way—in athletics, you’re always going to have that athlete who has ridiculously long femurs coupled with some tight Achilles. You may have eight weeks to get this kid jacked, and he can’t squat 185 lbs without his form breaking down. Is he weak? Is he not trying hard? No, he is biomechanically f***ed.
Now, he can’t squat deep, and when he tries, it turns into a mixed good morning and a squat. Then you’re compressing a sheering force and begging for someone to put a dumbass stamp on your head. Perception is reality in athletics. If your team looks jacked, people think your program is on point, regardless of how genetically gifted these kids are. Some of them come out of the womb yoked.
Be smart and check your ego. Believe it or not, there are other ways to get your legs and hips strong. Remember, I have eight weeks. This dude can’t squat to save his life and I need gains. Hit the leg press hard. Hit the reverse hypers and glute hams and work your adductors. I’m not sure what you’re missing? I can progress up to 20 lbs a week, especially in the first micro cycle of the year (off-season) on the leg press, and I now have tangible proof that this guy got stronger.
Torque Forces
Think torque wrench. You’re using a tool to place load on something in a twisting or rotational pattern. Think about what happens to your body in an exercise that has near maximal load in a rotational fashion. Some examples of exercises are rotary torso machines and land mine twists (certain variations). The rotary torso machine isn’t a bad piece of equipment, but the concern is more so how it is utilized or coached. This is a great way to hit all the abdominal muscles involved in rotating the body, but there has to be particular attention paid to how you perform a rep. You have to have your core set before you initiate the rotation, so squeeze your abs to set yourself up, move without any jerking whatsoever, and keep it controlled. If I don’t set my core and instead perform a relaxed jerking rep, I’m significantly increasing the chances of lumbar spine (disc) injury. Your lumbar spine isn’t made for mobility. The closer you get to your butt, the less mobility is intended.
This isn’t the most conventional example, but think about how we teach the bench press—tuck the elbows on the way down while ripping the bar apart, stay tight but really flare or flex the lats, and flare the elbows out away from the ribcage as you press up. In doing so, I’m experiencing compressive forces in the AC joint and torque forces around the GH fossa capsule or whatever the hell it’s called while placing sheering forces around the elbow. Just remember what athlete you’re getting and what this athlete has going on within his body.
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By now you’re thinking, “Well, what the hell can you do in the weight room?” Accommodating around your program isn’t always the easiest thing to do, but it’s a necessary evil unless you’re blessed with the healthiest team ever. I like and utilize most of these exercises. I will always try the squat and teach the squat intensely for quite a few sessions in a row, but I just don’t have the time to let gains go by the wayside. The bottom line is we all have to make sure we understand to a certain degree how the body works, how certain exercises affect the body, and what to do when an exercise isn’t the best choice for an athlete. If we have too much of an ego and put our exercise selection in front of our athletes’ physical well-being, we’re doing them absolutely no good and may potentially injure them. I definitely don’t know everything about injury prevention (if there is such a thing) or dealing with every injury, but I absolutely feel that this topic should stay in focus when we’re dealing with athletes.
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Rick Danison is in his second year as a strength and conditioning coach at Indiana University. He is a former all-conference football player and team captain at Ohio Northern University, where he earned a bachelor’s degree in exercise physiology, health, and physical education. He also has completed his graduate work in exercise science and coaching education from Ohio University. 
Any exercise can be risky if the athlete/client has a predisposition to injury in that area.
As much as I hate to be a pain about this as it is only spelling, but to me it immediately pulled from the effectiveness of the article, especially as I have my degree in mechanical engineering where pretty much everything is about forces.
it is spelled SHEAR forces, not sheer.
That set aside, good alternatives posted.
Great article Rick, I have an L-5 Stess fracture in my lower and RDLs and Good Mornings helped me prepare myself for my senior season of College Football at Marietta College. Good to see an OAC alum doing well. I’m about to graduate and am looking at OUs coaching education program as well. Any way I could contact you about some things and get some insight?
Do u box squat? Don’t understand why u would be doing leg extensions and leg presses.
What sports are u training for.
Firstly, it is shear, not sheer.
Secondly, you are mixing concepts. “the load is placed in relation to the center point of my lever (knee joint) and dictates a high level of sheer force” Shear has no relation to the length of the lever arm. That is moment. Draw a basic free body diagram and sum forces and you will find that this is the case. 100 lbs at 2 feet and 100 lbs at 2 inches will have the same vertical reaction but the difference is in moment, which is defined in inch-lbs, foot-lbs, inch-kips, foot-kips, etc. Shear at the point of rotation stays constant in movements such as good mornings, leg curls and curls. The moment varies because of the change in lever arm length due to the cosine of the angle times torso length.
“To make adjustments to this exercise, try a Romanian deadlift. It’s almost the same movement biomechanically, and in most instances, it allows for a greater load and cuts the sheer forces down drastically.” This is completely wrong. The concept you are looking for is that it reduces the tension on the lower back because force times distance in one direction (think torso length) will be resisted by force times length in the other (tension/compression couple in the torso at the SI joint).
“Now, he can’t squat deep, and when he tries, it turns into a mixed good morning and a squat. Then you’re compressing a sheering force and begging for someone to put a dumbass stamp on your head.” Again, this is mixing concepts. You are compounding a force by creating a larger moment by increasing the moment arm because of the flat angle and increased lever arm of the torso while maintaining shear on the spine and compressive forces on the hip joint. Draw a free body diagram.
Thirdly, the description of “torque” should be defined as “torsion” which is twisting about a longitudinal axis. The differences between moment and torsion would be best described by bending a pipe. Applying a force at one end and rotationally fixing the other end would develop moment (a cantilever). Torsion would be applying a pipe wrench and twisting it along the longitudinal axis.
When researching these topics, it is best to meet up with a civil engineer. They are the experts in this matter. I should know, I have a Master’s in Civil engineering and have been 10 years practicing. Or buy a statics book online.
I’m not trying to be a d*ck. Consider this a peer review.
It is great to see someone discussing theses matters.
Also, Mark Rippetoe does a great job discussing this in some of his lectures.
To Bif A
A little harsh on the review. Now that most people think you are either smart or a d**k do you feel better now?
P.S. I am a Structural Engineer for 26 years and it’s guys like you with your smart guy attitude that give us a bad name. You can’t rip someone publicly and then say, oh it’s just a peer review
Paul,
The review wasn’t intended to be insulting and was written respectfully. If it was taken differently, that was not the goal.
Peer reviews are rarely anything but harsh. Defending a thesis or paper is hell and receiving comments makes you better at the subject.
I expressed, and will continue to, that it is good to see someone go over these topics.
Good article Rick!
To Bif A, if you intend to start a review with a negatively phrased comment (i.e. “You are wrong, blah blah blah”…follow up with more “corrections” and then finish with a one liner stating something remotely positive. Engineer or not, you are percieved as a d*ck. I agree with Paul.
Bif, if you want to criticize constructively, you’ll need to change the tone of your writing, especially considering the context. No one asked you for your opinion, and you should keep that in mind.
I thought your comments were constructive, but they’d be better recieved if you delivered them more tactfully.
I think that it is great that “Biff A” reviewed this article and corrected it. Why would we not want information at the most accurate level? If he would of not came on here and did so, then individuals that do not know anything would go ahead and presume that the stated article was “accurate”.
To Josh,
Are you sure the article was “corrected” ? Just because someone writes down a bunch of terms that sound technical does that make it right?
To Biff,
You are obviously proud of your professional status. In two emails you feel a need to make sure everyone knows you have a masters degree and how tough a thesis defense is.
Congratulations to you. It is an accomplishment to be proud of, but don’t let it define you and don’t think it gives you a license to be a d–k.
No question an integration of classical mechanics (force resolution FBD’s etc) is relevant to this discussion and to training/lifting in general. I think what is too bad for you is that you don’t realize this article was not submitted as a thesis and there was no request for a “peer review”
If you don’t / can’t recognize how aggressive and negative your review was and think you should continue posting this kind of comment that’s too bad. I would suggest you reflect some on the reviewers comments. There is much positive to take away from the article. Your review goes from one negative to another , says you”should know” points the author to buy a book and points the readers to another source for their information.
Good luck in your personal and professional relationships with that approach.
Obviously I know it was corrected or I would not have stated such. I would have jumped on here to correct also, but I do not have the time…as I sit here typing wasting it, as people need to explore on their own for answers. The problem with that is to many people have the mindset of what is in print is fact, and are the either/or mentality.
Good article concept, poor execution.
I agree with Biff. While the author didn’t claim to have any engineering background or expertise, he attempts to use engineering terms in ways that doesn’t make sense. I wouldn’t write an article explaining anything about lifting using Kinesiology/Ex. Sci. terms that I don’t understand. It may have been more appropriate to email the author than post here, but he wasn’t rude and backed up everything he had to say.
Interesting article. Biffs review was maybe a little harsh but not terrible. People sometimes inject emotion when they read things and it’s often not the same emotion that an article was written with. All that aside, I love that Biff spoke up because people will very often accept what they read as fact. We are here to get better and learn the most accurate and up-to-date training principles. I’m going to dig out my Biomechanics books and review everything that has been said. If I find a civil engineer I’ll bring him into the discussion too.
To Josh J and Robert and anyone else that thinks what Bif said is a good comment. I agree that people take what they read as fact way too often. However, real professionals or at least good ones do not need to “correct” articles in a condescending manner and in actually takes away from the point of correction because it turns people off. Passionate or not..arrogant or not..right or wrong. If your intention is to correct, make it objective. For this site to continue to be a leader in the related disciplines…we need readers to make sure information is correct, however the egos and self praising can be left out in my opinion. I could interject all of my qualifications to strengthen a point…but if the point is accurate and true… It is never necessary!
Maybe I don’t know the purpose of this site here but when ideas are presented and another comes and challenges what was said, I have no problem with that, after all we do want to know that what is being said is true. Of course we can come to know that statements are true but still not possess a deeper understanding of what those statement imply.
I have no problem with Biff A. As long as he didn’t attack the man but rather the claims being put forth, he’s doing all of us a favor, and no where is it said that another can’t challenge what Biff A states as factual. So as far as I am concerned if we are dealing with a subject that is empirical then the conversation is never complete never final.
A lot of good thinking going on here.
This is a good article. Correcting the author could have been done more constructively, and to the least site some references so that the readers could look it up and judge for themselves what is fact and what isn’t. The bottom line is that we are all learning here. I don’t take everything I read for face value. I gather facts and do my own research. Build upon principles rather than take what one person says as truth.
First off, I like the spirit of the article.
Biff A –
While I do agree with your overall analysis of the applied forces, you simplified the overall model of the body a bit too much. If we were a axis, lever arm and force applied, then you would be very correct in your assertion. However, the body is a complex construction of many lever arms and distributed loads which allow us to accomplish any athletic (or everyday, for that matter) feats. Perhaps a bridge or other complex structure would be a better, but not perfect, analogy.
I am not sure if the author was meaning to explain the following, but application of a load like that would create shearing stress within the spine itself. Shearing stress at the vertebral level is very important to consider in regards to safety in an exercise, as well as appropriate exercise choice to match athlete skill level.
Thanks for the article Rick, and I hope you keep at it.
Thank you Biff A, I am glad you took the time to write all that down.
I don’t see why some of you guys feel the need to get all upset and start name-calling. You are reading into stuff that isn’t there.
I think we are all expecting only top quality information from elitefts, and I am glad to see the people contributing when they feel they got anything but the best. Those corrections were much needed, and I’m sure we’re all better off for it.
As I hope to put myself out there and start writing about exercise and nutrition, I can only hope I will have the good fortune of receiving such constructive criticism.
Thank u mechanical engineers! Haha , I guess I messed up torque and torsion and spelled “shear” wrong. I am not too prideful that I can’t admit when I commit grammatical sins and small things like that…… The point I was trying to make was more so understanding how to accommodate and understand how certaIn exercises effect certain areas. But u fellas also help bring to light how you can’t always apply mechanical principles to the human body. I mean hell according to the work equation isometric exercise is pointless……. Wall sits suck!!!!!!! Again I know how the little gramatikel miztaks
No sweat of my back. They take pride In Being an engineer, and I the same in my profession. Couple of small small details. I couldn’t build a skyscraper, a car etc. BUT am very confident about ability to understand and build a body, difference in collegiate/ practical learning between engineering and exercise phys, health, and physical education. Can’t help but feel like this is a situation like……. I say hip flexor and you say illiopsoas, I say glute and you say TFL and periformis. The “thesis” of the article was simply what I said in previous post. Thanks for clarifying