CrossFit Discussion Board  

Go Back   CrossFit Discussion Board > Community > Stuff and Nonsense
CrossFit Home Forum Site Rules CrossFit FAQ Search Today's Posts Mark Forums Read

Stuff and Nonsense For off-topic chatter. Keep it PG-13; no sex, politics or religion!

Reply
 
Thread Tools
Old 05-28-2009, 04:45 PM   #11
Jonathan Silverman
Member Jonathan Silverman is offline
 
Profile:
Join Date: Nov 2007
Location: Brooklyn  NY
Posts: 171
Re: Physics question

Quote:
Originally Posted by Tom Woodward View Post
It logically follows that more mechanical work can be done for a longer period of time while guzzling less ATP by NOT maintaining ideal isometric contraction of the lower back in an exercise like high rep deadlifts. Interesting stuff....
You won't be able to more work though! Because of inevitable injury if your lumbar extension goes.
  Reply With Quote
Old 05-28-2009, 05:29 PM   #12
Jared Ashley
Member Jared Ashley is offline
 
Profile:
Join Date: Nov 2007
Location: Tucson  AZ
Posts: 1,550
Re: Physics question

Quote:
Originally Posted by Tom Woodward View Post
Anyone intrigued by Jamie's post should check out this thread:

http://************.net/forum/showthread.php?t=5032 (not WFS due to language)

As Jamie says, isometric work generates zero work but requires energy consumption. This jives with Rip saying that more ATP is consumed while holding the erector spinae in ideal positioning than not, since that correct position for the lumbar is isometric. It logically follows that more mechanical work can be done for a longer period of time while guzzling less ATP by NOT maintaining ideal isometric contraction of the lower back in an exercise like high rep deadlifts. Interesting stuff....
hmm... I agree with mark's conclusion (intensity actually decreases when you bounce deads), but completely disagree with the reasoning behind it (a rather vague claim that the additional re-contraction of the erector spinae and the isometric hold somehow "burns more ATP"... maybe it's true, maybe not, but it's definately not a testable hypothesis). I'd say the REAL reason intensity decreases is that a substantial portion of the work (force * distance), is conserved during the bounce. At the bottom several inches of the pull, you're not generating 225 lbs of force, but some amount substantially less, therefore you're doing substantially less work.

More important is his *true* statement that the bounce is done to "increase the intensity with no attention paid to lumbar extention" and that that this is doing deadlifts WRONG. 225 is "light" for some, so they can get away with it, for awhile, without hurting themselves, but eventually it'll bite 'em in the a**!
  Reply With Quote
Old 05-29-2009, 06:43 AM   #13
Barry Cooper
Member Barry Cooper is offline
 
Barry Cooper's Avatar
 
Profile:
Join Date: Jun 2003
Location: Louisville  KY
Posts: 2,188
Re: Physics question

I would disagree that an Iron Cross is zero "work". The work being done is creating an equal and opposite reaction to the force of gravity. If the amount you are "falling up" is equal to the amount you are falling down, you are in equilibrium. The analogy I would draw would be to a treadmill. Objectively, you stay in the same place. However, you are doing work.

For my two cents--and this has already been approximately said--the relationship is a ratio between the total power POSSIBLE in a given setup--given the limitations of the human body--and the amount actually generated. For someone who is weak, you could do a perfectly efficient 95 snatch. And for someone who is strong, you could do a really inefficient 200 lb. snatch. Paul Anderson's form, for example, was terrible, even though he was our last heavyweight O-lifting champ.
  Reply With Quote
Old 05-29-2009, 08:15 AM   #14
Jamie J. Skibicki
Member Jamie J. Skibicki is offline
 
Profile:
Join Date: Jan 2008
Location: Pittsburgh  PA
Posts: 8,841
Re: Physics question

THe iron cross is zero mechanical work. Nothing is moving.

work = force x distance

distance = 0

work = 0


Also

work = change in energy
E = 1/2 mass * velocity^2

velocity = 0

E = 0

work = 0
  Reply With Quote
Old 05-29-2009, 11:44 AM   #15
Jonathan Silverman
Member Jonathan Silverman is offline
 
Profile:
Join Date: Nov 2007
Location: Brooklyn  NY
Posts: 171
Re: Physics question

I don't get it. Take Iron Cross, it is so hard. But it requires no work. I understand there is a neuromuscular component to this which is understated all the time. So it's about the coherence of the signal which has nothing to do with work.

anyway do muscles get bigger only because of the physics quantity of work? because it is an adaptation for better leverage. i refer to pg 83 of Starting Strength.

basically, getting big is about applying yourself as a lever a lot. i think the reasons gymnasts get ripped is because not bc they can do an iron cross but because they can do front levers and back levers.
  Reply With Quote
Old 05-29-2009, 01:21 PM   #16
Jonathan Silverman
Member Jonathan Silverman is offline
 
Profile:
Join Date: Nov 2007
Location: Brooklyn  NY
Posts: 171
Re: Physics question

imagine a definition of a strong mind using concepts of leverage.
wow...
  Reply With Quote
Old 05-29-2009, 01:47 PM   #17
Lee Sybert
Member Lee Sybert is offline
 
Lee Sybert's Avatar
 
Profile:
Join Date: Mar 2009
Location: Hattiesburg  MS
Posts: 37
Re: Physics question

Quote:
Originally Posted by Jamie J. Skibicki View Post
THe iron cross is zero mechanical work. Nothing is moving.

work = force x distance

distance = 0

work = 0


Also

work = change in energy
E = 1/2 mass * velocity^2

velocity = 0

E = 0

work = 0
But are you exerting engery, even with no motion involved. Your heart uses calories to beat and your body is moving something even though you don't see any external movement. Just a thought.
__________________
GO TEAM VENTURE!
  Reply With Quote
Old 05-29-2009, 02:01 PM   #18
Kurt Armbruster
Member Kurt Armbruster is offline
 
Kurt Armbruster's Avatar
 
Profile:
Join Date: Aug 2008
Location: Calgary  AB
Posts: 469
Re: Physics question

E=mv^2 is kinetic energy. There's no motion, so KE=0.

However, there's also the potential energy due to gravity one is fighting.

E=mass*acceleration due to gravity*height off the ground
  Reply With Quote
Old 05-29-2009, 08:26 PM   #19
Jared Ashley
Member Jared Ashley is offline
 
Profile:
Join Date: Nov 2007
Location: Tucson  AZ
Posts: 1,550
Re: Physics question

Quote:
Originally Posted by Lee Sybert View Post
But are you exerting engery, even with no motion involved. Your heart uses calories to beat and your body is moving something even though you don't see any external movement. Just a thought.
Yes, you are most definately burning energy, that isn't up for debate.

Also, Jamie is correct that zero "work" is done. It's physics 101, and also cannot be debated.

The term "work," when applied to isometric loads, is completely irrelevant. Remember that although you aren't doing any work, you ARE producing tremendous FORCE... it's just that no matter how large the force, the distance it's applied over is zero, and therefore force * distance = 0.

Muscle is strengthened NOT by how much "work" it does, but rather by how much FORCE is produced.

Do the math, and you'll find that very little work is done in a starting strength workout when compared to say, "cindy". But SS will make you stronger than Cindy will because you're producing a whole lot more force.
  Reply With Quote
Old 05-29-2009, 08:39 PM   #20
Jonathan Silverman
Member Jonathan Silverman is offline
 
Profile:
Join Date: Nov 2007
Location: Brooklyn  NY
Posts: 171
Re: Physics question

Why are you producing force in an isometric hold when there is no acceleration?
  Reply With Quote
Reply


Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is Off
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
A question regarding the CrossFit workout template and WOD with another question rega Andrew Chong Starting 6 08-06-2011 08:34 AM
Interesting Center of Mass/Physics Question Skylar Cook Exercises 6 01-24-2008 07:17 AM
A Unified Physics Theory of Animal Locomotion Court Wing Fitness 0 01-03-2006 11:16 AM
OT: Physics Bet with a friend Alexander Karatis Community 12 10-21-2005 10:42 AM
Iron Cross Physics Tyler Hass Fitness 6 12-08-2003 10:12 AM


All times are GMT -7. The time now is 05:58 PM.


Powered by vBulletin® Version 3.6.8
Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
CrossFit is a registered trademark of CrossFit Inc.