yup, this isn't new news, but im sure most people don't know that
although I guess some people think it does cause soreness because it damages mitochondria and other systems, which is why overtraining this way is potentially dangerous
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Disclaimer: I am not licensed to give advice in the fields of nutrition (yet). Consult a physician if you are unsure.
That is a very misleading article. Lactic acid doesn't cause the pain associated with exercise, but an accumulation of lactic acid in the muscles and bloodstream is a key indicator that the body is being pushed beyond its capabilities. Because of this, knowing your Lactic Threshold is still very useful in training. The article author just doesn't understand enough about the process to know why.
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Personally, there's not really enough information for me to make any kind of decision about it. The way I see it, from a common sense standpoint, is that anytime your body is using an unconventional energy source, its not running optimally. Yes, you will get better at running on lactic acid if you run on lactic acid routinely. Does that necessarily mean its good for you or ideal? I doubt it. It generates pain, pretty much everything else your body does that generates pain is telling you to stop. In any case, I don't think the impact of knowing the truth about it will impact sports/performance in any way.
Lance Armstrong and his lactic acid levels have been studied extensively. I'm not sure that the findings scientists have made regarding lactic acid and Lance (he produces less than most people) correspond to the findings in the NY Times article (lactic acid is used for fuel).
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Train the body as it truly is: one, flexible piece!