When I got back into cycling I started with a Semi-recumbent that was pure comfort. I started with 5-mile rides and moved to 10 and finally 25 mile rides. After about 500 miles I bought a MTB. The 500 miles was not wasted because my first dirt ride was 22 miles and other than discovering I needed to adjust the bar up and back I felt pretty good. About 150 miles later I got a road bike. My fitness level is getting better. My rides are now 100 to 140 miles a week. Whatever gets you to ride is what you need to get or maybe you need to just get to your LBS and have your bike adjusted and serviced. Not to take away from Nike but to get in shape, just do it.