[quote rjregh] I'm not in that good of shape, 63 y/o.
[/quote]
Would be in your best interest to not do it in my opinion, just not worth the chance of spending the balance of your cruise in a cast. The zipline is not necessarily strenuous as they pretty much have you strapped into a harness and you just ride the line, but as an example when you get to the platform you may need to take quick action to position yourself for the landing and if you don't judge right you will have to make some fancy last minute moves, FAST. On our last Mexico trip, granted not Costa Rica, one of our group splatted a tree, broke her foot/ankle, yup spent the rest of the cruise in a cast. And you will have signed a waiver saying that the zipline company is in no way responsible, even if the line were to break and you go to the bottom, it will be your responsibility to crawl out of the canyon yourself.........................