I think this is a physics question

[itsmefolks]

Here is my question and I hope this makes sense. My friend says that whilst on the x trainer in the gym they can use there leg muscles to press the pedals down when it becomes so stiff as to not be able to be pressed down under there own body weight! Ok! now….my reasoning is that if you have nothing to push the pedal against ie opposite motion stuff, ie the handle on the x trainer, your muscles alone cannot exert more pressure than your own body weight!! Does that make sense?? Thanks for any help.

[ll_billym]

Without holding on to anything else there are two ways I can think of more downwards force can be applied using muscles:

1) Shifting more bodyweight onto one pedal at a time, this will apply more weight onto each pedal than if the bodyweight was spread evenly across both.

2) Slightly jumping will mean that slightly more downwards force is applied when the bodyweight comes back down and hits the pedal.

[rov1100]

There once was an expert called Charles Atlas. He showed off a method to build up your muscles without weights or expensive gym material.

http://www.google.co....AQwAA&biw=981&bih=469

I think his method involved using your muscles aginst each other.

[rov1100]

Here is the method: It was called dynamic tension:

http://www.bodybuilding.com/fun/kelly4.htm

Therefore your example above is just using some of his techniques

[itsmefolks]

Thanks all. I may not be explaining the situation correct or very well.
See if this makes a reasonable question?
I am standing on a spring levered plank. My bodyweight alone is not enough to press it down. I am not allowed to jump or lean on it to one side to apply more direct pressure! Without jumping leaning, or pushing against anything, can I use my muscles alone to apply pressure to press it down?

[ll_billym]

If you bend your legs and straighten them (not sure whether you class this as jumping or not but your feet don't have to leave the spring) you will be lifting your bodyweight upwards against the spring, thereby pushing the spring down.

If you do this over and over again the spring will bounce up and down with you.

Technically this is not using your muscles to 'push' the spring down but you are just dropping your bodyweight and then pushing it back up again.

[itsmefolks]

Yea got that. This I guess is technically jumping although you say your feet wont leave the board you are actually springing!! My friend statement seems to defy the laws of physics to me saying just by muscle power the spring/lever can be pressed without external force jumping leaning or pushing!!! I`m not getting it at all! Any other suggestion gratefully appreciated and thanks for the help.

[wildwood]

Not familiar with your Xtrainer but if it has something to hold onto like handlebars, you can exert a force greater than your body weight.

Either that hold some weights or you can tie some weights around your waste. (watch where you hang them).

[ll_billym]

Ok, try it on a pair of bathroom scales. If you stand up you will weigh x, if you squat down, you will weigh x, but then if you stand up quickly the scales momentarily read a much higher number than x, not because you weigh more but because you put more downward force on the measuring spring when you push your weight away from it.

Not saying the above is absolutely true for cross trainers but the principle still applies - your friend is transferring weight somehow. The leg muscles do have something to push downwards against, it is the weight of the body above them.

[roger]

If your legs push down with more than your body weight you take off - jumping!

[venator]

I've not cycled for years, but used to have "rat traps" on my pedals. They held your feet so that you could pull up on one side while pushing down with the other. You could apply more than your body weight to the wheels.
Don't know if this is relevant - I did A level Physics in 1958, they may have changed it all since then!!

[itsmefolks]

Thanks everyone. I feel I have the answer now. I have not done Physics but common sense told me I was correct. My friend is convinced they are using leg muscle alone to press the x trainer down, ok! So if you have nothing to press against, not leaning, not jumping and just using muscle power, try it on a set of scales. I just have, and the answer is absolutely not. I think my chum is not realizing they are using a sideways body force to initiate the push. Basically to find the answer just stand on some scales and try and use your muscles to push the scales down. I`m afraid its impossible unless you exert an opposite force ie jump push or lean. And this will only be a momentarily reaction. Thanks for the scale idea and also everyone else I now feel like I have a valid discussion and cant wait for the gym tnite!! Hey hey!!