Discussion on the biomechanics of a pull-up and vertical jump

[Justin Waxman]

Hello,

This is my first posting and I am hoping that someone might be able to shed some insight on a discussion some of my peers and I have been having.

When doing a pull-up, it is common for individuals to kick their legs and bring their knees towards their chest in order to complete the set. In my opinion, this seems to work for whatever reason. What happens when individuals use this technique that allows them to complete the pull-up? Specifically, what is the mechanism?

Secondly, I believe that a similar mechanism is utilized when performing a vertical jump. When performing a vertical jump, trained athletes will use their arms during the counter movement in order to achieve a greater vertical height than they would be able to achieve without the use of their arms.

I look forward to hearing your feedback,

Justin

[Dan Robbins]

Re: Discussion on the biomechanics of a pull-up and vertical jump

Hi Justin,

I would suggest that in both cases the additional movements create momentum which provides an impulse in the direction of movement and aids overall performance (hence the higher vertical jumps noted with the use of arms). We actually run a biomechanics labs for our first year undergraduate students looking at the vertical jump the effects moving the arms or keeping them crossed over their chests - it’s a very consistent higher jump with the use of arms.

I have never tried to measure the effect of leg movement during pull ups. I suppose if you estimate the weight of the leg (via body proportionality tables) and measure the velocity of the movement it wouldn't be too hard to estimate the momentum and factor in how much help leg movement provides the exercise. Could be an interesting study!

Hope that helps
Dan