MIS is more strength oriented and PH is more endurance oriented. Cathe uses a 35 lb. barbell for every single body part in MIS (legs, chest, back, shoulders, bis and tris). Ans as you know, in PH she uses 15 lbs for bis or 25 for tris, etc. MIS is a good workout and can be easily split so you can do upper body one day and lower body the next. I use MIS when I'm doing a Pure Strength rotation and want to get an addition weight workout later in the week. Cathe posted a rotation once where you do PH 2x's per week and MIS 1x a week for 4 weeks, then you do PH 1x and MIS 2x's for 4 weeks. That is tough! I am always of the opinion that the more variety in your weight work, the better, but that is just me. Hope this helped. Have fun!