“Keep mental stress contained. Mental fatigue is physical fatigue. Work, family, not enough time listening to music or laughing or being with friends will take a toll. Be happy and your running will benefit. Ian Thompson, a famous British marathoner once said, “When I am happy I am running well and when I am running well I am happy.” This quote exemplifies what I have found to be true.”

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Matt Fitzgerald is the author of numerous articles on running at Active.com, Competitor, and elsewhere. 

http://teachtorun.com/2013/03/09/