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Correct Lifting Technique
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Correct Lifting Technique - June 29, 2001 6:25:00 AM
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mcap
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Group:
A few nights ago I was watching yet another episode of the Metrx strong man competition. Those things never cease to amaze me. The event in question was lifting a barbell that was comprised of two gigantic tires above the head starting from the floor.
Every contestant kept their legs almost completely straight!!! I was waiting for some PT to jump out of the audience and correct their lifting posture and to tell them to bend their knees (and correct their pelvic alignment while they were at it).
In ergonomics presentations by our collegues I always here the same thing. Lift with your knees not your back. Who said this was true??? What is it based on?? Why do we persist. This isn't science based advice it is only traditional advice that we didn't even need to go to school to hear.
The back has more tourque generating capapcity and fatigue is less likely when you lift with your back. Squatting is appropriate for some people, in some situations, but not all. The most important thing is to keep the load close.
mcap
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Re: Correct Lifting Technique - June 29, 2001 8:30:00 PM
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mcap
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Cat:
One should consider whether the advantages gained from their lifting techniques are from training alone. My point is that there are physiological advantages as well. The average person, off the street, with no training, could just as easily hurt themselves with a bent knee lift particularly with something similar to a barbell where it would require moving the load further from the body.
SJ:
Do you mean people that work in a contiually flexed position. Because in that case, many people do actually fatigue their muscles and end up hanging on the ligaments and passive tension.
If it is repeated flexion you are talking about, then I agree. They use those muscles all the time.
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Re: Correct Lifting Technique - July 1, 2001 2:50:00 AM
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henryryry
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From: Brisbane, Australia.
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I remember reading "Physical therapy for low back pain" by Twomey and Taylor - there was a suggestion (I think it was by Nic Bogduk) that it doesn't really matter whether one bends the knees or not. Apparently, studies have shown in industries, the biggest factor is how close the weight is to your body - there was little difference between crouch and stoop lifting when it came to injury rate (there were 2 studies commented on).
However, in saying this, I am not suggesting that we should all lift in with our knees straight or bent. It really depends on the nature, frequency, weight etc.... I don't think the answer is that simple.
Just a story to consider... I saw a patient last year who complained of knee problems. He said that he had always lifted >50kg for about 20 years and did it correctly at the knees.... no wonder he had little meniscus left in the knee.
Henry***
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Re: Correct Lifting Technique - July 1, 2001 8:00:00 PM
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mcap
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Henry:
I agree with you. There is no one correct way. It depends upon the person, the load and the situation.
mcap
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Re: Correct Lifting Technique - July 5, 2001 11:08:00 AM
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mcap
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Senior Cat:
Your post was well......interesting in a deliverance kind of way.
But, I must take issue with you on several points. No matter what you are doing, moving the load closer reduces the moment arm.
And, more importantly, you are forgetting an important point. You are discussing a straight leg lift as if the flexion and extension all come from the lumbar spine. Furthermore you assume very little flexion extension of the lumbar spine during a knee lift. But this ain't necessarily so.
Remember that when you do a stoop lift, the majority of motion is at your hip joint. Thus allowing the mighty and powerful glut max (as well as the hamstrings) to get in on the act. Your lumbar spine only moves as much as you reverse curve. Theoretically, you could have very little motion there. In a bent knee lift you may have a great deal of curve reversal.
So.....like we always say it depends on the person and the situation. So far, people have looked into it and they have found no difference.
Check out this Meta-analysis. Full text is available through medline.
Stoop or squat: a review of biomechanical studies on lifting technique.
Clin Biomech (Bristol, Avon) 1999 Dec;14(10):685-96
CONCLUSION:
The biomechanical literature does not provide support for advocating the squat technique as a means of preventing low back pain.
mcap
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Re: Correct Lifting Technique - July 5, 2001 1:38:00 PM
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mcap
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Sorry Cat!
Of the two....I would say the first one is the safer lift.
I followed the link but I don't necesarily agree with their reasoning. Look at the second picture. As the knees extend, the spine will still have to extend, producing a significant moment on the spine exacerbated by the increased moment arm.
Furthermore, there is a physiological cost associated with squat lifting. Workers may start out with it but they will inevitably switch to stoop lifting as they tire.
mcap
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Re: Correct Lifting Technique - July 5, 2001 3:29:00 PM
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henryryry
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From: Brisbane, Australia.
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mcap and bobcat:
I think we are all leaving out a very important part of the equation, which is the make-up of the person involved. For instance, a 150cm solid laborer vs a 180cm skinny machine operator trying to lift the same weight. I am very interested to know whether there were any studies that considered this aspect.
But I think we can all agree that there is no safe way of lifting for everybody.
Henry***
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Re: Correct Lifting Technique - July 6, 2001 7:37:00 AM
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mcap
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Senior Cat:
While I can almost understand what you wrote, I think you are trying to hard to prove soemthing that many people have looked into and no one has proven. The truth of it is that even the examples you cite, while long and complex are still riddled with assumptions and simplifications that may lack validity.
Look at the second diagram. The spine is still flexed even though the knees are bent. As the knees straighten there will be a moment produced at L5/S1 that is higher than anything in the other diagram. There are so many questions we don't know. What is the contribution of the quad? What about the motor control and fatigue. What is the contribution of the passive elements of the lumbar spine such as ligaments, fascia, passive elements of muscle, etc.
Also, we must be careful in using statics to discuss kinetic problems. The moments are really equivalent to the mass moment of inertia multiplied by the angular acceleration. AND.....all of this assumes CONSTANT aceleration. If it is irregular.....and it is, then we must start using calculus for the equations.
The Cornell website discusses the NIOSH lifting equation. However, this is not a strictly biomechanical analysis. A lot of the background research involves the workers perception of the load, not just the actual load. This is a factor as well.
So......it is a complicated picture. But again, I will reiterate. You cannot simply say that bending the knees is better for you in every situation. If biomechanics is your thing, then I will plug both scenarios into the Utah back equation and see what I come up with. If I have time [IMG]http://www.rehabedge.com/forums/smile.gif[/IMG]
mcap
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Re: Correct Lifting Technique - July 6, 2001 8:02:00 AM
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mcap
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Cat:
Using the Utah simplified back equation with approximations of the joint angles in the two pictures I am coming up with 623 ft-lbs of compressive force at L5-S1 for picture one and 693 ft-lbs of compressive force at L5-S1 for the second lift. (I assumed a 30 lb weight, too tired to make the conversion. I kept the horizontal distance intact.
The truth is that we are not even sure of how we can lift a 30 kg weight at all. The muscle forces and passive tensions don't even add up. So I would hesitate before drawing any conclusion about lifting styles.
mcap
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Re: Correct Lifting Technique - July 7, 2001 5:25:00 PM
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sarty
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From: Florida, USA
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I'm following this thread with great interest.
I have 2 things I'd like to share.
1st of all, I work in a work performance/PT clinic, and they have body mechanics classes going all the time. They show the "correct" way as the squat lift. I have heard it said that when the lordosis is lost in the lumbar spine, that the force needed to support the upper trunk increases significantly (as the upper body falls more in front of the plum line), and that that force, in addition to the weight of the object being lifted, is very stressful.
Secondly, I know that when I try to lift with a hip hinge but no squat, my low back hurts. If I do a squat lift, it does not. I am not in the best shape in the world, however, and I know we've been theorizing that that could be a big factor.
Well, those are my 2 cents [IMG]http://www.rehabedge.com/forums/smile.gif[/IMG]
Jen
[This message has been edited by sarty (edited July 07, 2001).]
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Re: Correct Lifting Technique - July 7, 2001 6:18:00 PM
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mcap
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Jen:
For you perhaps, the squat lift is better. But I think you should really take a look at the article I posted. It is usually available in full text from medline.
You could loose or maintain your lordosis in either type of lift!
PT instruct people on correct lifting techniques all the time!! But, in my opinion, giving someone one blanket way to do it all the time is detrimental. Techniques should vary depending on the lift, person and situation. As a profession, we really don't know and haven't figured out the best way to lift things.
A really nice way to adjust lifting technique is to observe or film them doing the lifts they actually do at work. Then you could use one of the back equations (NIOSH, UTAH, etc) to come up with areas of concern. But these are only ROUGH tools and to my knowledge, have never been fully validated.
At a recent ergonomics course one of the participants stated that no lifting instruction program has ever been shown to reduce injury. No one in the room offered an argument.
Food for thought!!!!!
mcap
mcap
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Re: Correct Lifting Technique - July 9, 2001 2:59:00 AM
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henryryry
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From: Brisbane, Australia.
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Mcap, you are quite right to say that when you use the equation, the passive and muscle structures don't add up to 30kg torque force. There has been an interest in biomechanics on lifting, and whilst I am not an engineer, I have read a bit on this topic (especially on the rigid-can theory, the passive structure theory etc). The fact is (as mcap said), nothing is proven, and probably won't be proven unless one considers all the factors (which is probably not going to be possible in a single study).
Henry***
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Re: Correct Lifting Technique - July 9, 2001 6:50:00 PM
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mojo
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From: ga
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pretty interesting thread and topic,
i see where you (both) are coming from bobcat and mcap. using many complex equations and material others have researched and have there own opinions on is a true lawyers way of explaining what doesnt necessarily need to be explained or even have an explanation.
the stoop and the squat i believe is the main issue at hand which is better?...
i think that there is no best as previously stated, its a general equation you are bringing to a specific body. many people have longer legs than others, others have longer torsos...some have shorter arms or longer arms..etc. i could go on forever. but mainly it all has to do with the angle of pressure on the spine and the knees. when squatting you will surely alleviate pressure on the spine by utilizing more of the leg ..and putting more stress on the knees ( which adds even more problems to the body and also brings pressure to the spine at a new angle). but, lifting from the back is putting all the pressure on that one particular point on the back. to solve this problem one would need to know the body type length of legs knees ...angle at which all the pressure pushes on each joint in the body which to me is just completely ridiculous, AND a waste of time. this is a problem that doesnt necessarily need to be solved or even have a correct answer...these are the facts of the matter:
the best way for someone to lift a certain amount of weight or an object is the way in which they are the most proficient (or the strongest)...which in this case of the strong man competion they must have been more proficient and felt stronger lifting with there backs rather than using there legs.
there really is no proof to this and mainly why i agree with mcab in that matter...niether way is better...completely depends on the person and there particular body makeup or structure.
take care,
Mojo
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Re: Correct Lifting Technique - July 9, 2001 7:10:00 PM
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mcap
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Mojo:
I agree with your post 100%. And......as a bonus.....you have saved me from having to do math on a Monday [IMG]http://www.rehabedge.com/forums/smile.gif[/IMG]
mcap
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Re: Correct Lifting Technique - July 10, 2001 1:44:00 PM
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mojo
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From: ga
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i see your point bobcat,
i think you are right when stating what i had said and about the pointlessness of figuring something out that requires such mathematical genius, that you obviously have. just seems to me it was a rather simple question with a not so simple answer. that was mainly all i was trying to state, not in any way discredit all the data you have come forth with. and, with all the different possibilities (weight being lifted, angle of object away from S1/L5, force in which object is lifted..etc.) it would take a rather long time to explain a very complex question with a simple answer.
which is better squat or stoop?
answer : niether
but i do find your math , and all of your formulas interesting to say the least , and the perceverance in which you go after finding the solution to such a vast question...cheers!,
mojo
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Re: Correct Lifting Technique - July 14, 2001 9:36:00 AM
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Rennie Maeda
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From: Manhattan Beach
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Bobcat,
Thanks for the great links!
There was a study that showed that African women could carry up to twenty percent of their body weight without increasing their oxygen consumption. Larger loads did require more energy, but the increase was only half that needed by the American soldiers carrying the same weights. The African women carried the loads on their heads! [URL=http://208.245.156.153/archive/output.cfm?ID=547]http://208.245.156.153/archive/output.cfm?ID=547[/URL]
Clearly there must be increased compression throughout their spine equal to the weight they are carrying. How would this fit in to your equations?
One way to keep the flexion moment at zero would be to carry the weight under the pelvis, with one arm in front of the body and the other in back, but you would need long arms and this would make it difficult to walk!
I want to know if you think that leaning the trunk back, through hip extension, would also decrease the flexion moment or force and thus the compression. I often tell my patients to carry things this way. I have them carry a 25 pound box at pelvis level, and feel the stress on their back decrease as they lean their trunk back, either by extending their hips or flexing their knees. (try it).
If one had a bad back, and excellent hips and knees, one might be able to lift or pull in this manner (with enough backward lean to balance the flexion moment).
Also, doesn't the oft heard admonition "tighten your abs" increase the flexion moment and the necessary reaction moment and therefore the compression?!?
Rennie
[This message has been edited by Rennie Maeda (edited July 14, 2001).]
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Re: Correct Lifting Technique - July 14, 2001 9:42:00 PM
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henryryry
Posts: 100
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From: Brisbane, Australia.
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To all:
I am impressed by all the equations and maths involved in such a simple lifting example, and further shows that the issue is multi-fatorial. Just something to make your brains tick.... many equations on lifting assume that the moments act on solids. But as we know, soft tissue and even bones have different properties to solids. Will the equations that Bobcat proposed, which may well work for solids, also apply for soft tissue??
Henry***
ps- I had to revise my high school mathematics to follow what Bobcat has done.... it brought back some memories!
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