its the low-ends and pulsing reps. the legs especially kill me,but b/c of all the different tempos and long sets its best to go lighter on this workout. i tried it once with 50lbs barbell and hurt my back pretty bad, now i stick with 36lbs for legs and 25lbs for upper body.
kassia
When they discover the center of the universe, a lot of people will be
disappointed to discover they are not it -- Bernard Bailey