I need to buy some builders trestles for the upper courses of my internal garage blockwork and I will be working off a newly laid level concrete floor.   I reckon 11 blocks will get me up to a decent height for the roof joists.   Lifting a 15kg block up to the 7th course caused a few painful twangs in my elbow tendons so I would like to keep the lift differential to 5 blocks or say foot to chest height. Working the maths backwards this suggest a max trestle working height of