Originally Posted by
Machka
That's normal.
You might try a different saddle, or experimenting with shorts.
Also make sure your front wheel is raised.
And it helps to get off the trainer every 30 minutes to stretch a little bit. Sometimes I ride 30 minutes, then do some stretching and core work, then ride 30 minutes, and repeat.
+1
I dismount and do sit ups and push ups for every 15 or 20 minute interval. This practice extended my trainer endurance considerably.