For someone new to exercising or very overweight, don’t try to start out at a superstar level. Not only will you hurt yourself, but you may get turned off and give up on exercising. I can’t tell you how many people I have seen get stress fractures trying to do too much too quick. Now that is a motivational killer!
To get started and without straining to the point of pain, take a sample PT test and see where you are at (this will be your baseline to measure your progress). Secondly, start off doing half your max for each exercise you performed in the PT test for your push-ups and sit-ups and build up from there. For detailed instructions, get a copy of my book, MAX Out the Army, Navy, Marine, and Air Force Physical Fitness and Combat Fitness Tests.
Do exercise on a regular basis! At least 3 days a week, but 5 or 6 days is preferred. Do a combination of aerobic (heart rate 70%-85% for 20 minutes) to burn off fat and anaerobic (strength) to build muscle (the workouts in this book do both).
If you are recovering from an injury, don’t try to start off where you left off before your injury or serious reinjury may occur. If it has been months since exercising, follow the guidance in the preceeding paragraph. If it has only been weeks and you are beginning to feel good, you can be a little more aggressive, but you need to listen to your body. If it says, “no,” don’t push it too hard. In either case, get a doctor’s approval first, especially for major injuries and consider physical therapy. Those therapists can guide you through the process.