i cant really tell because im not platinum, but it doesnt look like you're squeezing your back muscles and flexing them at the end. i was taught to do that and in turn every muscle in my back is sore from deads the next day. but then again you're about 400 lbs bigger than me and could probably throw me across greenland with one finger, so dont take my advice seeing that you probably know way more than me judging your figure. i should just buy a pink bookbag and get it over with.