This was a nightmare for me, but J Schwizzle's tips really helped. One more thing I thought I would add for this achievement is that when transitioning from squats to the lunges you can actually do ski jacks for both the next sections. I was able to get most of my numbers from this and hit 300 after 3 rounds through the cycle. Also for jump squats you don't have to squat all the way down. The main thing was throwing your hands in the air to keep the bar up.
Just keep going at. This achievement had me so pissed off yesterday. I was at 275 and I was lunging no problem and all of a sudden the bar dropped. I was so sore from trying to get this achievement as well. Just plug away and remember it's a good thing you don't have a controller in your hand for this one. I'm sure I would have thrown mine at the tv yesterday :)
For those that don't know what a ski jack is here is a video of some random dude doing them on youtube:
**Also please note that you do need to be in some sort of shape to do this achievement. I am honestly in good shape and my heart rate went through the roof on this achievement, so if you're a couch potatoe I would say avoid this or actually play through the game (cause it is a good work out) and attempt this last or forget it.
If you vote negative please let me know why, thanks :)