It depends on the ride. On woodies, hands up all the way all of the time except at certain times. Sometimes on a mega helix, I hold on. On all drops on steel or woodies, OSTR's or lap bars, I also have my hands up. On launch coasters, I usually keep my arms down because of the intense forces on my body at launch. On Hypersonic XLC, I kept my hands up though on the launch, it was great. On loops I usually keep my hands down because there is no point of keeping them up on the loop in my opinion. I hate fighting with OSTR's. I can put one hand up usually but I can not seem to get both hands up at once. Basically on drops, hands always up. On loops and launchs, hands down, and hands up sometimes and hands down other times on helices... (usually up though) The biggest mistake I made was putting my hands up on the Jack Rabbit at Kennywood. On the double dip, I had my hands up and I went literally out of my seat and basically was standing up. There basically is no lap bar and I went flying out of my seat. The person next to me was pushed out of his seat also but literally grabbed my shirt and had to pull me back into my seat because he was afriad I would fall out. The next ride, I put my hands down on the lap bar but I still got pulled way out of my seat.... it was intense and great.
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Dave