Noticed something

Question
Rick
I like to plod along at about 4mph on my treadmill every evening after work.
From a true runners standpoint it might be better to run outside,but you dont know my neighbourhood,and besides I watch the news and sports while on the treadmill before I do the evening chores.
Anyway,this might sound funny,but I switched over to a 30 minute news show from a 60 minute show,
I figured I better run faster to compensate for the shorter running period.
It was tough to go from 4 to 5 mph but I am doing it.
I have noticed that I am gettng some tingling in my calves and thigh muscles after about 20 minutes. No pain,but its almost as if I am stimulating new muscle fibres from the increased speed.
I have heard of fast and slow twitch fubres and have researched a bit online but there is no real agreement.
Is the faster running in fact stimulating the production or at least awakening of my fast twitch muscles?
Also,my weight loss has picked up a bit too.
Thanks,have a good summer.


Answer
A change from 4mph to 5mph does not have a major effect on fast or slow twitch fiber usage.  The tingling you are feeling is perhaps just more increased blood flow, not 'fibers being awakened', as those fibers are already there, they just haven't been placed to higher demands, and really, fast twitch fibers demand a much faster & more powerful demand than just a 5 mph jaunt.  Research on fast & slow twitch fibers is still in the discovery process, from my standpoint.  More is being learned about it each year in the labs & real-world testing by trainers & coaches.  I don't think your 1 mph is increasing any demands on the fast twitch fibers.  
For some ideas on shorter workouts, I would suggest reading my free guide, The Mini-Max Method, found at http://speeddialcoach.com

Rick Karboviak