A simple exercise that works up to 75% of your muscle at the same time, strengthens back and stomach, trains balance, heart & lungs and gives you a cardio workout, no equipment required... you can do it anywhere anytime... how cool is that?
As cool as squat.
Simple knee bends, where you align feet shoulder-width apart, keep back straight, bend knees over toes, go down gently as deep as you're comfortable with - but never more than to a 90 degree angle.
Do it right. Follow these guidelines.
Squats are not just for weightlifters, and they don't need to be very advanced. Be careful to warm up your knees gently first, and start at a level that feels right for you; don't go too deep but try to get your thighs working. It's a perfect exercise to start with at home, you can do 15 repetitions waiting for the kettle to boil, another 15 while the tea is steeping. Max effect for minimum time!