I think many of the critical people on this thread don't have a basis for criticism unless they are at least 35-40 or more and have experienced their body becoming less resilient, and have had a period of time when they have had to completely stop exercising for at least 3-6 months due to pregnancy while working full-time, major injury/illness, or working 100 hours a week while on business travel. Continuing with exercise is a lot easier if you find something you enjoy doing. For me, those were running, hiking, dancing, and biking. Barring that, have a form of exercise where you noticeably feel better afterwards. Some forms of yoga have that effect on me. One major problem with beginners is that they don't know how to start out at an appropriate training level.When I took up running in my mid-20's, I increased mileage and intensity properly, but I was wearing crosstrainers that I had been wearing daily for a year. I also ran on concrete and did stretches I'd learned in high school sports that didn't include all running-appropriate ones like calf/achillies tendon ones. If you have lower body injuries, that can keep you from doing a lot of the more accessible forms of exercise. I'd go to gyms and ask them if they had arm bicycles. They would tell me that those only existed in physical therapy offices. I wish I had heard about deep water running 10 years earlier.