I was looking through the excellent text book "Physics" by Giancoli (4th Edition and very battered) when I came across this interesting problem about a 90kg weakling who couldn't do even one pull up. 90kg is quite heavy for a weakling, maybe he can't do a pull because he's too heavy rather than too weak. I remember the Charles Atlas from the 60's, he was selling his dynamic tension body building program and had adverts in all the comics. The adverts usually features a 97 pound weakling having sand kicked in his face. That's 44kg so I guess something has been lost in translation. However someone who only weighed 44 kg would probably be able to do a lot of pull ups. I sent off for the brochure but never subscribed to the programme. A little later in life I was tempted by the Bullworker adverts and as a result I can now do quite a lot of pull ups.