I purchased Insanity a few years back and only lasted for 3-4 workouts. The workouts were too difficult for me and although I enjoyed it, I just failed to commit to it. Fast forward to July of this year..... I am not even sure why I attempted it again, but I am glad I did. First things first; this program is physically challenging to the point that I would recommend anyone going into it be cleared by their doctor BEFORE starting. Seeing a physician after you've injured yourself is the equivalent of closing the barn after the horses got out! There, it's been said. Now on to my review of this product.
I did the original P90X and gained a lot of upper body strength. The one issue with the original P90X is that, after weeks and weeks of doing the videos, you start to realize how much Tony talks and how much time you're wasting -- standing there with your weights -- waiting for him to start the exercise. What I love about the + videos is that he cuts most of that out. It's straight to the exercise and he barrels through. It's a little disorienting in the beginning, as you don't know how to do the exercises at first, but it's so nice knowing that I can be finished with the workout in 30 minutes, instead of 60 for most of the regular P90X DVDS.
Video Abstract for the ESSR 46.4 article “Modulation of Energy Expenditure by Estrogens and Exercise in Women” from authors Kathleen M. Gavin, Wendy M. Kohrt, Dwight J. Klemm, and Edward L. Melanson. Reducing estrogen in women results in decreases in energy expenditure, but the mechanism(s) remain largely unknown. We postulate that the loss of estrogens in women is associated with increased accumulation of bone marrow–derived adipocytes in white adipose tissue, decreased activity of brown adipose tissue, and reduced levels of physical activity. Regular exercise may counteract the effects of estrogen deficiency.
In extreme instances, over-exercising induces serious performance loss. Unaccustomed overexertion of muscles leads to rhabdomyolysis (damage to muscle) most often seen in new army recruits. Another danger is overtraining, in which the intensity or volume of training exceeds the body's capacity to recover between bouts. One result of detrimental overtraining is suppressed immune function, with an increased incidence of upper respiratory tract infection (URTI). An increased incidence of URTIs is also associated with high volume/intensity training, as well as with excessive exercise (EE), such as in a marathon. Marathon training requires the runner to build their intensity week to week which makes them more susceptible to injury the more they increase their mileage. A study shows that in the last 10–15 years up to 90% of marathon runners have suffered a physical injury from their training.
Thus, little is known about the effects of monitored vigorous exercise in elderly people. While significant benefits for basic motor tasks (such as balance and gait) can be achieved through different kinds of physical activity (i.e., stretching exercises, treadmill, Pilates, and strength and balance training), no conclusive relationship has been proven between its intensity and such improvements. Recently, Pau et al.  reported that spatiotemporal gait parameters and sit-to-stand performance significantly improve through vigorous (but not light) exercises, thus suggesting that higher levels of intensity might be more suitable in generally improving static and dynamic daily motor tasks.