xeon2k

I usually don't have a problem riding Mantis once; but after 2 rides, my calves can't take it any more. I've never had issues with my knees or crotch area (it's not that comfortable, but not much worse than a bike ride). I have had the G-Forces cause my leg muscles to cramp up like a charlie horse. That can definitely ruin your day of walking through the large park. Usually one ride is OK for me, if that. Sometimes, i skip the stand-up coasters all together to avoid possible leg / muscle cramps. Good Luck!