Mike Boyle had a great post on this today....I'll quote:
I thought physiologists knew at least something about conditioning. Boy was I wrong. First they tell me anaerobic threshold, then they tell me lactate threshold, then they say ventilatory threshold.
I could have figured out ventilatory threshold on my own. How's this for physiology: If people work really hard they'll pass the ventilatory threshold. In other words they will get out of breath. Wow, people who exercise get out of breath. Unfit people get winded faster than fit people. Thank god I took all those classes.
I'm back to work capacity. Vern Gambetta was and still is right. Forget physiology and energy systems, just figure out the game and train for it.
As for fitness, if you listen to the "accumulate 200 minutes a week" folks, prepare to quit your job. Who has that kind of time? Once you're healthy enough to exercise, exercise hard. Walking is a waste of time, so is jogging. Run intervals if you have no joint issues and reasonable body composition. If you're overweight or have any lower extremity problems, buy a Schwinn Airdyne and ride intervals. Long steady state work is for recovery days only.
If you're an endurance athlete please try to ignore me. I'm not talking to you. When you get hurt, just remember I told you so.