I actually started Insanity on September 11, 2013 by taking my initial fitness test (results and progress below). I tried to stick with the schedule as much as possible, although with work, travel and other commitments here and there, I had to take some days off out of sequence. During those time periods, I tried to still do some yoga and stretching exercises to help keep up. As such, it took me about seven weeks to enter Week 6 of the Insanity training program.
It did not take more than about 2 weeks for me to notice a definite improvement in my strength and endurance, and also to have at least one person comment that she noticed a subtle change in my appearance, that I looked more "in shape". By the end of the first month, I also found I was able to do certain exercises I never could before, like repeated full push-ups instead of push-ups from my knees. I felt much stronger in my arms and shoulders especially, and was pleased I could now just about finish some of the most intense 40-minute routines with only a few breaks - when I first started I could barely get through half of them.
I can say, however, that I did not lose any weight after starting the program, despite efforts to eat "cleaner" and watch my calories. Admittedly I did not following the dietary plan that goes with the workout as it's just not practical for me and my lifestyle. In fact, I actually found at the end of the first month it appeared that I had actually gained several pounds, which had not been a welcome outcome! But I did some reading and it turns out that may be a common occurrence and not true weight gain but water retention, due to not drinking enough water and muscle inflammation from the high-impact exercises. So I increased my water intake significantly and did notice, after my "Recovery Week", that the weight gain seemed to go away. Some people say you will see weight drop by the end of month two.
Below are my fitness test results on Day 1, Day 15 (after two weeks of Insanity) and Day 36 (after 5 weeks of insanity). The fitness test consists of 8 exercises, where you keep track of how many of each you can complete in one minute.
Sockii's Fitness Test Results
Exercise / Day 1 / Day 15 / Day 36:
Switch Kicks: 124 / 123 / 136
Power Jacks: 45 / 51 / 60
Power Knees: 100 / 114 / 123
Power Jumps: 25 / 41 / 48
Globe Jumps: 7 / 8 / 8
Suicide Jumps: 13 / 15 / 16
Push-up Jacks: 11 / 23 / 34
Low Plank Oblique: 48 / 72 / 76
These results definitely back-up the Insanity promise of improved stamina and endurance - especially for me for upper-body exercises like the push-up jacks and low plank obliques.
I confess, I did not end up finishing the full 60 days of the program because the "Max" workouts were just too intense for me. I also was truthfully getting bored of doing these same workouts over and over again and wanted to go back to varying my routine with using cardio and weight training equipment at the gym, along with other home workouts.
So I suppose my experience with Insanity was a bit mixed; it worked as a sudden "shake-up" in my routine to improve my endurance and muscle strength, for a time. But for me it was too tough of a workout to see through in the full 60 days. Perhaps if I had been fully committed to also following the dietary regime I would have seen better results. But this is a seriously intense workout program that is not going to be for everyone.