What do you guys think of this:
If you engage in long duration cardio keep it easy so that the slow twitch fiber does the work. There's a big difference between running a 4.5 minute mile and running an 8 minute mile. The former will make you weak and slow as your body calls upon fast twitch fibers which must adapt to accomplish the task. The latter won't have any negative effects because the slow twitch fiber can handle the workload. The development of lactic acid is a sure sign that you're recruiting fast twitch fibers. Make sure the lactic acid stays out of your legs and keep the intensity to 60-70% of maximum heart rate.
From this article:
"And for crying out loud. Don't go into the pain cave. I can't stress this enough. Your Totem Animal won't be in there to help you. You'll be on your own. The Pain Cave is for cowards.
Pain is your companion, don't go hide from it."