Hey all, I'm new here.

I recently changed jobs, and, to put off purchasing a $438 parking permit, I decided to ride my bike in to work (and back home), about 12 miles round trip, while the weather is still nice. I just have a cheapo $100 Walmart mountain bike, but it gets the job done.

My question is more related to fitness - I don't generally exercise, so this has been a bit of a startling experience to my legs. They are very much fatigued after riding! Also, I have a good deal of pain (normal muscle building pain) when going up small hills, etc. So, how long can I expect this muscle-building pain to last, if I ride 12+ miles each day 5 days a week? When will hills no longer be a big deal?

It generally takes me about 35 minutes to make the ride one direction, so about 10.3 mph average. I'd like to get that down to 25 minutes travel time, or about 14.4 mph average. Is this a practical goal on a mountain bike?

And finally, will I completely lose all of this taking 9 months off bike riding, and have to "start all over" in July of next year if I want to continue riding? I can't start riding earlier, as I have severe grass allergies, unfortunately.