How do you programmatically execute transition?

I have a content type that uses node field. I am trying to programmatically change state of node and add comment to the transition. I've looked all through D.o and workflow module documentation but don't see an example of doing this. I am currently changing state by loading the noded updating the SID of saving it. I feel this approach is kind of sloppy and don't see how I would add comment to the transition if this is the proper way to do it.