I also noticed if the game speeds up many times. It actually stops speeding up and sometimes returns to normal speed. Also, I could barely run on the treadmill at 27, but then it went to 41 and I ran on it fine (seemed like 18).
Once I figured this out, it helped encourage me to complete the quests, knowing the game works against itself.
I'm still working for the 50,000 point quest, though I've only gotten to about 47,000 points, I think.
Anything beyond 35k points is completely luck. I had to try around 40 times before I finally didn't get stuck with a ridiculous amount of speed increases.
This is the only game for which I may never try to achieve the quests. It's appropriately named (thanks John). I'm almost done with all of the other current quests, so it'd be nice if more came out so I don't end up grinding Saurus. I'll do it! I'll ...
A bit of advice for everyone having trouble with the 50k calorie quest.
Hold down the jump button when the treadmill isn't moving in a way you like. From that point, all you have to do is watch the spikes and time it so you land in front/behind them and not on them, and the wind speed. Only try for running on the treadmill when the wind helps balance you out, or if it's not pushing you one way or another too fast.
When I first tried this game I couldn't get past 10 000. The next day I played it again and before I knew it I was a 30 000. In the end, I got 55 000 and 3 quests in one run. I still need to get the "Ten Spins, None of the Calories" quest. That one is probably the hardest.