What is the difference between running fast for a short distance and slow for a long distance?

Sometimes I go running with my sister, and she runs pretty slow but for up to 7 or 8 miles. It usually take over an hour (and if we walk or rest, up to two). I always complain that it takes too long and would rather run two or three timed miles (in, let's say, about 20 minutes). What are the physical... show more Sometimes I go running with my sister, and she runs pretty slow but for up to 7 or 8 miles. It usually take over an hour (and if we walk or rest, up to two). I always complain that it takes too long and would rather run two or three timed miles (in, let's say, about 20 minutes). What are the physical differences between the two different styles of running?
8 answers 8