For many years, lifting with straight knees and a bent back was considered harmful to your back. You had to bend in the knee and lift with a straight back to avoid back injuries. This is a belief which Professor Jens Ivar Brox from the Department of Physical Medicine and rehabilitation at the Oslo University Hospital in Norway challenges in an editorial comment titled ’Lifting with straight legs and bent spine is not bad for your back’ in the journal Scandinavian journal of Pain.
Jens Ivar Brox has penned the editorial comment because the latest edition of the journal includes a paper, which examines pain free persons beliefs about bending and lifting, especially with around back posture. The paper disclosed that the participants in the survey perceived that it is dangerous to lift with straight knees and a bend back.
This belief originated in studies from Sweden among other places, which recommend lifting with a straight back and bent legs, based on studies evaluating disc pressure in the back in various postures and in lifting.
Jens Ivar Brox disagrees with this belief. He points out, that studies of Swedish lumberjacks indicate that thigh exertion is higher when lifting with bend knees than when lifting with straight knees. There is a possibility that the lumberjacks prefer this movement strategy, which mostly reduce the demands on the knee-exertion muscles.
The studies of the lumberjacks have shown that the knees are not the weak link when performing hard physical work such as lifting, it is the thighs. The warning not to lift with a bend back can cause more damage than good in the public because the focus is wrong.
Read Jens Ivar Brox’s editoral comment here: https://www.degruyter.com/downloadpdf/j/sjpain.2018.18.issue-4/sjpain-2018-0302/sjpain-2018-0302.pdf