What does it mean to be fit?
Webster's tells us that fitness is "the capacity of an organism to survive and transmit its genotype to reproductive offspring as compared to competing organisms"; Dr. Fred Hatfield, in his book Fitness: The Complete Guide, gives us a more layman's view by defining it as: "Your ability to meet the exigencies of your lifestyle with ease and room to spare for life's little emergencies." Both definitions refer to functioning in the present as the main indicator, meaning that all these studies on heart disease in aging individuals probably aren't even the best bases to use to make conclusions about an individual's state of fitness. Fitness is, in the simplest terms, your ability to perform in the world. We all have different goals and agendas and, in the end, we're all going to die. But there are a few things that we all share, no matter what kind of life we lead. If we consider the eight parameters below, and if we can perform them decently, we can consider ourselves to be fit. And, more than anything else, a fit life is probably a lot more fun than a non-fit one.

This is how efficiently your body transports oxygen. It's a baseline fitness parameter that aids every more intensive fitness effort, from yard work to sex to running a marathon. Indicators of good aerobic fitness are a low resting heart rate and the ability to recover quickly after cardiovascular activity. You help increase this endurance by doing any type of activity but more efficiently when you do continuous low-level activity, like hiking or jogging.