I agree with chiffonade. As a former bodybuilder and health nut I've come to believe that that level of building muscle is anything but healthy. In all my years reading various magazines on health and fitness, Runner World offers the reader sound advice. The muscle-mags are full of self-promotion and misleading advertising promising quick fixes in a bottle or little pill. On another note, though, everyone must continue to do weight-bearing exercises 2-3 times per week in addition to aerobic exercise. For one, it's within the muscle tissue that metablism takes place therefore the more muscle a body has the more metabolism or break down of calories can take place even at rest. Secondly and especially for women (although it still applies to men), weight-bearing excersice helps build and maintain bone mass. Women peak on bone formation at the age of 30, so if you're not lifting weight you are losing bone at a rate of 1-2% per year after that age. Too much bone loss and you have osteoporosis which now leads in mortality rate over breast cancer. So pick up your dumbbells!!