It means raising the elbow up to stop the blow/attack. It could mean raising the elbow up directly in front of yourself, like here: http://www.google.co.uk/imgres?um=1&hl=en&sa=N&tbo=d&biw=1252&bih=591&tbm=isch&tbnid=eUxxX-nmWz-7yM:&imgrefurl=https://twitter.com/bob_breen&docid=TVNa2Fgjg6TNDM&imgurl=https://si0.twimg.com/profile_images/318867782/Bob_High_Elbow.JPG&w=500&h=623&ei=NHzNUIigJYTJ0AWc-IHIDA&zoom=1&iact=hc&vpx=4&vpy=27&dur=2872&hovh=251&hovw=201&tx=101&ty=122&sig=115671142989749020050&page=2&tbnh=156&tbnw=125&start=22&ndsp=31&ved=1t:429,r:30,s:0,i:183 -- Alternatively it could mean rotating the elbow upwards to the side, kind of like in the picture below (imagine the person is standing up lol): http://www.google.co.uk/imgres?um=1&hl=en&sa=N&tbo=d&biw=1252&bih=591&tbm=isch&tbnid=1hfsvyS-RAxbGM:&imgrefurl=http://www.swimsmooth.com/injury.php&docid=v-m9sbJk2PdpyM&imgurl=http://www.swimsmooth.com/images/HighElbow.jpg&w=289&h=151&ei=NHzNUIigJYTJ0AWc-IHIDA&zoom=1&iact=rc&dur=472&sig=115671142989749020050&page=1&tbnh=120&tbnw=224&start=0&ndsp=22&ved=1t:429,r:2,s:0,i:94&tx=128&ty=51 -- All that "raise my arm at the elbow" really means is "raising the elbow" whether that's done straight ahead or to the side. -- Good luck and take care :)!

You wouldn't even need the "at the elbow" part. So just say, I raised my arm to ward off the blow. or I tried to block the blow/punch with my arm. / I blocked the blow/punch with my arm.