Anyone working in a work positioning harness (read tree work) day-in-day-out needs to set aside and hour of their time to watch this presentation by Dr Roger Mortimer from the National Cave Rescue Commission.
Dr Mortimers' presentation was video taped at the 2012 NCRC National Seminar.
The content is clinical but Dr Mortimer does translate the most important points into tree climber's language. This is an excellent presentation for anyone likely to be involved in an aerial rescue.
Well worth an hour of your time.