Surprisingly tough. Just finished the 1st week, so at the end of next week i will be doing all 10 reps instead of 15 reps for 2 weeks, then after that down to 5 reps. When you use such lightweight but use really strict, controlled form, it is a lot harder than you think. I mean lat raises with 15lb dumbbells doesn't sound too tough, but when you really focus on using the delts to lift them, it surprisingly tough. All in all good though, looking forward to the 5 rep weeks. Id recommend it for someone wanting a change from the typical workouts.