The answer to your question would be that in the sentence above the word "detach" means the following: separate from.
"Detach" means "to disengage (something or part of something) and remove it. It also means "leave or separate oneself from". The fact is that pedal straps increase the efficiency of your pedalling by allowing you to pull you up as well as down. They hold your feet tightly. Therefore, if you fall, it is necessary for them to detach themselves to avoid any fracture. Taking all this into account, it can be said that, in this case, "detach" means "separate from" because that is what the pedals do when the person falls.