Push-ups with feet on stairs above body's CoM -- Why does it seem harder?

[Melbourne Guy]

TL;DR Summary

If I do push-ups off the floor as you'd normally do, they're hard enough. But if I elevate my feet on stairs, so my body is horizontal at the start, they feel harder. Are they?

I've been slowly increasing my push-up count, using the traditional pose:

For a lark, I thought I would try it with my feet on the stairs, so my body is horizontal at the 'up' position with my arms fully extended. It turns out, this seems to require a lot more effort:

But am I actually doing more work, or is it just that the unfamiliar posture makes it seem that way?

I've been trying to figure out if the 'feet on stairs' position puts more weight on my arms, but I can't see that it would because the same four points of my body are supporting my weight. Or, it might be that my centre of gravity is shifted with the feet on stairs, and that causes me to be lifting more weight...but that doesn't seem right, either.

Any thoughts on whether it's all in my head? Or are my arms really trying to tell me something?

 

[PeroK]

More of your body weight is on your arms in the second position. It must be about 50-50. In the first position there is more weight on your feet.

Do a free body diagram!

 

[Lnewqban]

Summary: If I do push-ups off the floor as you'd normally do, they're hard enough. But if I elevate my feet on stairs, so my body is horizontal at the start, they feel harder. Are they?

I've been slowly increasing my push-up count, using the traditional pose:

View attachment 304124

For a lark, I thought I would try it with my feet on the stairs, so my body is horizontal at the 'up' position with my arms fully extended. It turns out, this seems to require a lot more effort:

View attachment 304125

But am I actually doing more work, or is it just that the unfamiliar posture makes it seem that way?

I've been trying to figure out if the 'feet on stairs' position puts more weight on my arms, but I can't see that it would because the same four points of my body are supporting my weight. Or, it might be that my centre of gravity is shifted with the feet on stairs, and that causes me to be lifting more weight...but that doesn't seem right, either.

Any thoughts on whether it's all in my head? Or are my arms really trying to tell me something?

The angle of the body changes, but the location of your center of mass does not shift.
Think of both extreme positions: standing up straight on your feet only (100% feet/0% hands), and on your hands only (0% feet/ 100% hands).
Please, see:
https://www.physicsforums.com/threads/the-physics-of-the-inclined-pushup.953338/

https://courses.lumenlearning.com/suny-physics/chapter/9-6-forces-and-torques-in-muscles-and-joints/

 

[Melbourne Guy]

Do a free body diagram!

Thanks, @PeroK, I've had to look that up, but I can now see why there is a difference...and why my naive thought that "my weight is my weight" wasn't quite right!

 

[Melbourne Guy]

Please, see:
https://www.physicsforums.com/threads/the-physics-of-the-inclined-pushup.953338/

OMG, @Lnewqban, great link, I'm slapping my forehead that I didn't look first! Thank you for doing my research for me

 

[pinball1970]

OMG, @Lnewqban, great link, I'm slapping my forehead that I didn't look first! Thank you for doing my research for me

I was never keen, it always hurt my lower back and gave me a headache!

Dips remove that pressure and your triceps lats and side chest still get a good burn.

Bench press is still best to build your pecs, seated in the machine if you have no spotters.

You have a gym near you? Do they safety tour first.

During Covid I did dips in the bath! You put your feet where the taps are grip either side and you can go as low as you need.

 

[Melbourne Guy]

Dips remove that pressure and your triceps lats and side chest still get a good burn.

I've actually no idea what those are, @pinball1970?

 

[pinball1970]

I've actually no idea what those are, @pinball1970?

I'll post. You young guy Yes?

 

[Astronuc]

Dips remove that pressure and your triceps lats and side chest still get a good burn.

I've actually no idea what those are, @pinball1970?

Basically, one positions oneself between parallel bars, or perhaps two chairs, with hands on the bars/support, then assuming arms are extended vertically, one bends the arms, lowers the body and the pushes up. One could support ones feet on another support (method describe by pinball) or curl legs underneath. Otherwise, between parallel bars about 1.5 m from the ground, one can keep one's legs vertically.

One should probably keep a cushion underneath so that if one's arms collapse, or one slips, one does not receive a hard landing.

 

[Melbourne Guy]

I'll post.

Thanks, and also to @Astronuc for their description (and cushion advice), much appreciated

You young guy Yes?

Not so much anymore, @pinball1970, I'm on the short glide down side of life, now