ExRx.net

Exercise Prescription on the Net
It is currently Tue Sep 02, 2014 9:45 am

All times are UTC - 6 hours [ DST ]




Post new topic This topic is locked, you cannot edit posts or make further replies.  [ 12 posts ] 
Author Message
PostPosted: Tue Feb 05, 2008 5:08 pm 
Offline
n00b
n00b

Joined: Tue Feb 05, 2008 5:03 pm
Posts: 3
Does anyone know how mean power is calculated for the vertical jump calculator in exrx.net.


Top
 Profile  
 
 Post subject: It's physics
PostPosted: Tue Feb 05, 2008 11:20 pm 
Offline
Rookie
Rookie

Joined: Mon Feb 04, 2008 7:24 pm
Posts: 24
Location: Norfolk, NE
The fine people use the information that you supply and do something similar to what is described by this:
http://en.wikipedia.org/wiki/Power_(physics)

I don't know exactly either?


Top
 Profile  
 
 Post subject:
PostPosted: Wed Feb 06, 2008 6:00 am 
Offline
Deific Wizard of Sagacity
Deific Wizard of Sagacity

Joined: Thu Mar 02, 2006 5:49 am
Posts: 3474
I can't answer your question, but it made me think of a previous discussion on here. It actually wasn't really on power, but it almost got hijacked by some, erm, debating which is why it seems a bit all over the place. but there's some great info,

Really, your looking for the discussions about power with Kenny Croxdale, who is very knowledgeable on the subject :-)


http://exrx.net/forum/viewtopic.php?t=4 ... c&start=15

Hope that helps

KPj


p,s some good links in that thread, too.


Top
 Profile  
 
PostPosted: Thu Feb 07, 2008 7:15 am 
Offline
moderator
moderator
User avatar

Joined: Sat Mar 10, 2007 5:44 pm
Posts: 6401
Location: Halifax, NS
nelson wrote:
Does anyone know how mean power is calculated for the vertical jump calculator in exrx.net.


I can't speak for the actual calculation used in the calculator, but

power=work/time or forcexdistance/time

In this case, force is equal to your weight, distance is the height of the jump and time is calculated from the height and gravity.

Stu


Top
 Profile  
 
PostPosted: Tue Feb 12, 2008 6:02 pm 
Offline
n00b
n00b

Joined: Wed Dec 12, 2007 9:03 pm
Posts: 5
Location: Wales
stuward wrote:
nelson wrote:
Does anyone know how mean power is calculated for the vertical jump calculator in exrx.net.


I can't speak for the actual calculation used in the calculator, but

power=work/time or forcexdistance/time

In this case, force is equal to your weight, distance is the height of the jump and time is calculated from the height and gravity.

Stu


As mentioned here, to calculate power in Watts in a physical way:

Power is energy dissipated per second.
Energy is work done.
Work done is force x distance.
Force is your body-weight in kilograms multiplied by upward acceleration.
Upward acceleration would need to be in excess of 9.81m/s/s.

You could work out the minimum power produced by:

Multiplying body-weight by 9.81 then multiply by change in height. With this answer divided by the time taken.

To get the absolute power you would need to know your final upward velocity.


A simple although not entirely accurate way would be to calculate the gain in potential energy, which is the (change in height) x (acceleration due to gravity) x (body-weight). Then divide the potential energy by the time taken to produce the change in height.

Example: Person of weight 100 kg. Gravity is 9.81m/s/s. Change in height 1m. Time taken 0.5s.

100 x 9.81 x 1 = 981 Joules

981 / 0.5 = 1962 Watts


Top
 Profile  
 
 Post subject:
PostPosted: Tue Feb 12, 2008 6:36 pm 
Offline
moderator
moderator
User avatar

Joined: Sat Mar 10, 2007 5:44 pm
Posts: 6401
Location: Halifax, NS
I had to plug your numbers into the calculator to see if it gave the same answer. It didn't. It gave 2401.

I found this site:
http://www.topendsports.com/testing/ver ... -power.htm

They had 4 different calculations, all gave different answers and all were different than the calculator.


Top
 Profile  
 
 Post subject:
PostPosted: Wed Feb 13, 2008 8:00 pm 
Offline
n00b
n00b

Joined: Wed Dec 12, 2007 9:03 pm
Posts: 5
Location: Wales
stuward wrote:
I had to plug your numbers into the calculator to see if it gave the same answer. It didn't. It gave 2401.

I found this site:
http://www.topendsports.com/testing/ver ... -power.htm

They had 4 different calculations, all gave different answers and all were different than the calculator.


What I said was a raw theoretical analysis. Calculate the power by working out the change in potential energy and dividing that by the time taken to do so. It does not take other factors into consideration such as momentum, air resistance etc.


Top
 Profile  
 
 Post subject: Vertical Calculation
PostPosted: Tue Feb 19, 2008 4:54 pm 
Offline
n00b
n00b

Joined: Tue Feb 05, 2008 5:03 pm
Posts: 3
Thanks for the responses.

I tried to calculate the power using potential energy or using kinetic energy, but my calculations were way off what was in ExRx.net.

I though if I found it on the internet it must be true.


Top
 Profile  
 
 Post subject:
PostPosted: Sat Apr 05, 2008 10:37 pm 
Offline
Apprentice
Apprentice

Joined: Sun Dec 23, 2007 9:14 pm
Posts: 152
Why don't you try running up several flights of stairs instead (say all the way up a 12 story building)?

Power is the change in potential energy (your weight x total height obtained) over time (the time it took to climb all those stairs).

It's all legs - just like jumping.


Top
 Profile  
 
 Post subject:
PostPosted: Sun Apr 06, 2008 10:37 pm 
Offline
moderator
moderator
User avatar

Joined: Thu Feb 07, 2008 7:11 am
Posts: 7503
Location: Kudjip, Papua New Guinea
Nelson--What are you using the calculation for? Comparing one athlete with another? Measuring your own progress over time? I'd think that if it's not for some scientific study where precision is essential, that you could just pick a method and use it consistently.


Top
 Profile  
 
 Post subject:
PostPosted: Mon Apr 07, 2008 6:50 am 
Offline
In Memoriam: TimD
In Memoriam: TimD
User avatar

Joined: Mon Dec 19, 2005 8:04 am
Posts: 3129
Location: Va Beach, Va
JD, I think you are right. I've seen this topic on the vertical come up many times. Most often, what is recommended are fairly heavy squats, to estblish a strength base in the hips/glutes/quads, followe by some OL pulling motions from the floor, and some 2nd pull variations. The 2nd pull is basiclly kicking the hips in combined with a jump shrug with a heavy barbell. This works pretty well. However, when it comes to Vertical Jumps for basketball stuffing, LOL, the best method I've ever seen came from a women's Basketball coach, and she went and bought one of those adjustable hoops, and then had the gals stuff at a given hieght, and then slowly raised the bar = so to speak. She didn't worry, or care, about scientific studies, she just got her ladies out there and adapting to the height increases.
Tim


Top
 Profile  
 
 Post subject:
PostPosted: Tue May 06, 2008 7:07 am 
Offline
n00b
n00b

Joined: Tue Feb 05, 2008 5:03 pm
Posts: 3
Jungledoc

Thanks for the response. I am really just trying to motivate myself to improve. I just got curious how the math and physics worked and figured there would be a precise calculation.


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic This topic is locked, you cannot edit posts or make further replies.  [ 12 posts ] 


All times are UTC - 6 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 2 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Powered by phpBB® Forum Software © phpBB Group