It’s 6:45 a.m. in the middle of January and not that cold in Tucson, Ariz., where I’ve joined the SaddleBrooke Masters for one of their five weekly workouts from September through May. The 6:45 group is the first of three groups of Masters swimmers. Each workout lasts about 90 minutes and ranges from 1,500 yards for beginners to 3,000 yards for the more experienced swimmers.