I'm 73-1/2 with a 23 year-old graphite heart valve, usually feel really good, so can hunt 4-6 hours without much pain, lo! For some reason I don't require much water during the hunt, maybe a swig it two. Due to obligations, I don't get out near as much as I'd like. But, like Mr. Callihan once said. .."A man's gotta know his limitations".....sometimes I probably exceed mine, lo!