Fast twitch muscles

Question
John
I have gone from being a turtle,running at 4 mph on my treadmill for 15 minutes,to where I can now go comfortably at 4.5 mph for 30 minutes.
My next goal is 30 minutes at 5 mph.
Does this mean I am developing more fast twitch muscle fibres,or am I just getting fitter?
Also,I will be playing soccer next week.Sounds like a dumb question I know but will I be faster on the field?
What is a good goal in terms of speed and time to go for? I am 48 years,5'8",about 25 pounds overweight(but losing). Thanks!  

Answer
Hi Barry
Sorry no fast twich,just getting fitter.Yes you will be more effective on the field.Don't worry about the goal barry,just keep ajusting your program as far as duration and speed and it will take care of itself.Just enjoy the process and losing those 251bs and getting healthy.You have many years in front of you,and being consistent and having patience is the key to the future.

To your continued success

John