Question: why we are feeling tired when we run for a longtime? 

Answer: because you used a lot of energy . . .\nyour muscles lactate which causes muscle pains . . .\nyou don't have enough energy . . .\nyour body is not used to it . . .\nyou don't exercise regularly . . .\n\netc . . .\n\n:p
This question from the Yahoo Q&A forum is categorized in the topic: Sports