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Biomechanic Question
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Biomechanic Question - April 27, 2007 4:24:00 AM
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JSPT
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Consider 2 ways of doing a sit-up:
Person is supine with the hips flexed and in ER and the bottoms of the feet facing each other:
1. The person crunches up until they reach a sitting position.
2. There is a support (such as a Dynadisc) under the lumbar spine which starts the spine in an extended position and the rectus in a lengthened position, relative to technique #1. The person then crunches up until they reach a sitting position, exactly the same as in #1.
Question: What are the considerations for variations #1 and 2? Will starting a muscle in a lengthened position as opposed to the standard position work the muscle harder? Is technique #2 a "better" exercise than #1? Any reasons to not do one or the other?
Assume this is for a college-level athlete with no musculoskeletal conditions or abnormalities; the exercise is for conditioning only.
I'm not asking why you would do this exercise or how it would relate to function, etc. I'm just trying to figure out the biomechanics/physiology at play.
Look forward to the responses!
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JS
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Re: Biomechanic Question - April 27, 2007 5:13:00 AM
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allenbr4
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Just curious to hear why you have the hips externally rotated. Reduce psoas activity?
Thanks.
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Re: Biomechanic Question - April 27, 2007 1:07:00 PM
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Tom Reeves DPT ATC
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I think it would not make any difference on the first rep because the static stretch of the RA does not excite the contraction. Subsequent reps might be assisted by the stretch reflex or the RA if one rep immediately follows the other. Like plyometrics.
That said i think there are better ways to train the abdominals.
Of course.:-)
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Re: Biomechanic Question - April 27, 2007 8:54:00 PM
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Rwantz
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I agree with Tom, there are much better ways to train the abdominals. I feel that the abdominals are the most overtrained muscles in the body. I prefer a focus on the entire core, and not the abdominals at all.
That said, to me it seems that starting in more of an extension position would strengthen the muscles in more range of motion, but would not make the exercise better per say. I would say the instability of the DynaDisc would require more core stabilization and would be a progression from the first.
Consider function. How functional is either one of these exercises. Granted they do have their place.
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Re: Biomechanic Question - April 30, 2007 2:38:00 AM
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Sebastian Asselbergs
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"Question: What are the considerations for variations #1 and 2? Will starting a muscle in a lengthened position as opposed to the standard position work the muscle harder?"
It will just work the muscle in a greater range - the speed and number of reps dictates the actual labour performed by the muscles.
"Is technique #2 a "better" exercise than #1?"
Depends on the purpose of the exercise. #1 is better for that particular range of function. #2 is better for THAT range of function.
"Any reasons to not do one or the other?"
Yep. Don't do either - unless it's for beach- esthetic value....
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Re: Biomechanic Question - April 30, 2007 6:04:00 AM
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JSPT
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What about the length-tension relationship and the all or none principle?
Does contracting through an extra 10% of the range of the muscle really make it "work" harder, assuming that the load is not increased?
As far as I know, strength gains are directly correlated to the load the muscle needs to overcome, not how much it has to shorten.
I hear all the other "why even do this" arguments, but I'm just using it as an example to figure out the biomechanics/physiology.
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JS
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Re: Biomechanic Question - May 1, 2007 10:06:00 AM
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Tom Reeves DPT ATC
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OK. You are correct, strength is a measurement of how much load a muscle can overcome, not how much it has to shorten. I would say that contracting through the extra 10% ROM does not necessarily make it work harder, but through more range. The load IS increased however relatively speaking because in the lengthened position, the muscle is less efficient. Therefore, the load is increased relative to the contractility of the muscle.
IF however, the muscle is quickly stretched, the stretch reflex will be initiated and contraction will occur with less concious effort and so a bit more stretch (provided it causes no facet compression pain) would accentuate that.
I subscribe to the philosophy that it is better to make a muscle smarter than it is to make it stronger.
Given the choice I would choose a smart weak muscle over a strong stupid one. that is why I am more concerned about WHEN a muscle contracts first, THEN how much force it generates.
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Re: Biomechanic Question - May 2, 2007 11:38:00 AM
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JSPT
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Great answer, Tom. That's what I was getting at. Now, let's move on.
Two variations on a biceps curl:
1. Single-arm curl with 10# from 0-90 degrees elbow flexion for 20 reps.
2. Single-arm curl with 10# from 0-130 degrees elbow flexion for 20 reps.
Caveat: The athlete does not perform any activities which require forceful bicpes contraction past 90 degrees, but does require forceful shoulder flexion from 0-90 degrees.
Again: I know the functional arguments for not doing this exercise, I'm just trying to use a very specific, easy example.
Between the 2 methods above, will either exercise make the biceps stronger than the other exercise(generate more force)?
Beyond that, consider these 2:
1. Single-arm curl with 20# from 0-90 degrees elbow flexion for 20 reps.
2. Single-arm curl with 10# from 0-130 degrees elbow flexion for 20 reps.
(the athlete cannot lift the 20# weight between 91-130 degrees)
Would the muscle get stronger using the full range or by lifting a heavier load in a smaller range?
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JS
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Re: Biomechanic Question - May 2, 2007 1:28:00 PM
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FLAOrthoPT
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get stronger at midpoint? get stronger in eccentric load? get stronger in specific range? after 90 degrees the vector of the force decreases significantly that 10 pounds may only be 5 pounds of effort at 115 degrees, so theoretically work is force over distance, so the force is higher in sheer weight on the 20# but the distance is less, and the distance is greater but the force is less to begin with and as it goes above 90. So it comes down to functionality, though you want to avoid the subject. the muscle would be stronger at mid range (traditional testing point) with the heavier weight with same reps.
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Re: Biomechanic Question - May 2, 2007 7:35:00 PM
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Rwantz
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The muscle would get stronger 0-90 in theory, but not through the entire range. You are obviously strengthening the biceps through a partial ROM and so the muscle, which is already strong in that ROM is able to do more work than at the end of the ROM. My thought, although I am not sure where you are taking us on this ride, is that there is no reason to strengthen the biceps 0-90 ONLY if the strength deficits exist beyond that. I would not say only work 90-130. I would work the entire ROM with a weight that is appropriate for the entire ROM. If there is a restriction on the last 40 degrees then you would focus on only 0-90.
I do like the point brought up above. I am an advocate on eccentric control in strengthening.
To answer your question specifically, a muscle only is strengthened in the range that it is worked. Doing 20# in a short range is going to do little for the other 40 degrees. There is the thought that there is strenghening occurring 5 degrees on either side of isometrics. Is this applicable? I think that there is some application here.
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Re: Biomechanic Question - May 3, 2007 5:02:00 AM
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Tom Reeves DPT ATC
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I agree with Rwantz You will strengthen in the range that you exercise + or - a few degrees and at the same velocity + or - afew degrees per second with more carryover going from high speed to low speed, and more carryover from high force to low force.
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Re: Biomechanic Question - May 4, 2007 1:57:00 AM
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JSPT
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"To answer your question specifically, a muscle only is strengthened in the range that it is worked. Doing 20# in a short range is going to do little for the other 40 degrees. There is the thought that there is strenghening occurring 5 degrees on either side of isometrics. Is this applicable? I think that there is some application here."
Is that true? What about the "all or none" principle? If the bicep completely fires anytime it is contracted, how do strength gains become specific to a portion of the muscle?
The reason I started this thread was becasue a colleague went to a course about a week ago which taught abdominal crunches using a pad under the lumbar spine, with the hips in ER. Their theory was that by starting the rectus in a lengthened position, you make the muscle work harder, and therefore will build more strength in that muscle.
We both agreed that it was a non-functional exercise. It just got me thinking about whether or not working a muscle beyond its normal contraction range would really make it stronger than when the muscle is limited to a smaller percentage of its length.
Great answers, everybody. Thanks for taking the time.
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JS
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Re: Biomechanic Question - May 4, 2007 5:36:00 AM
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Tom Reeves DPT ATC
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JS typed: "Is that true? What about the "all or none" principle? If the bicep completely fires anytime it is contracted, how do strength gains become specific to a portion of the muscle?"
All or none is an action potential, not a muscle contraction. You obviously can contract muscles at various intensities, otherwise everytime you picked up a stryofoam cup you would crush it with your maximum grip pressure.
If you progressively increase your effort, you recruit more motor units and therefore, increase force.
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Re: Biomechanic Question - May 4, 2007 8:00:00 AM
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Shill
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Good point Tom.
Crushing styrofoam cups still makes me feel like The Hulk though.
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Re: Biomechanic Question - June 6, 2007 10:25:00 PM
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Randy Dixon
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I think what you need to look at is fulcrums and length of levers. If you place a support under the back these are different than unsupported. Also, if you only strenghten through the range of motion that you train, would you say that if I did isometric contractions and went from say, 100 pounds/MVC at 90 degrees to 300/lb MVC @90 deg. that my MVC at 110 deg. would remain unchanged? Do you think that athletes who train functionally and virtually never squat to their full depth don't develop strength at this deeper position? If you took an untrained person, with fairly weak legs, trained him on a steady diet of hill climbs, heavy resistance biking, some heavy box squats etc. that their strength at a full squat would remain unchanged? Is it possible to have extremely strong biceps through, let's say 0-45 degrees, weak biceps through 60-100 and extremely strong through 110 to complete flexion?
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