I have taken up swimming to save my knees and hips; really enjoying the workout. I generally have about 30 minutes twice a week to get the heart rate up and improve the swim technique. I can swim slowly for longer times, more turtle like from end to end for maybe 6 laps and using easy breast stroke. Or i go vigorously for two laps, free style or butterfly, really get the heart pumping then rest for a few minutes and go again. My preferred is the latter, really work hard, then rest a bit, work hard again. Any opinions on aerobic function and these options.