We don't need Loomis or tracing for this exercise, just the power of our brains. You are still retaining everything you studied this morning whether you realize it or not. So not really worrying about specifics but just the forms and how they interact with each other.

Notice in the image how the bicep fits into the deltoid, or the forearm is drawn as a cylinder on top of the upper arm. I do this on purpose like its a sculpture or legos. You don't want to try to connect the dots with lines afterward, instead put the pieces together in the blocking phase. Then it is easy to add other muscles or details over your accurate forms. If you can't do this then go back and build simple objects and gradually increase the specific details. You are never too good to go backward. Never guess when you can find out and don't waste time finding out. Do it right now.

Once you draw one arm this way then try rotating it slightly in another direction. You will remember little details from the previous drawing to apply to the new one. Analyze. Figure it out. That is how you learn and remember.