1. I have never had full blown AMS, but have felt it's effects a couple of times. I have only summitted Whitney once, flew in and spent one night spent at HM and a second night in route at UBSL. No issues for either my son or I on that trip. I have also been over 13k several times, (multiple summits of the Grand Teton and other places in the Rockies and Cascades), with no real AMS.
2. I did not train any specifically for Whitney or most other trips to the mountains, but I do run quite a bit and strength train 3-4 times/wk primarily with my kids in our garage. I don't wear a HRM. Typical week would be 3-4 runs during the work week of usually 8 miles each and a long run on Saturday of 12 to possibly 20+ miles if I have a marathon approaching, (12-15 miles would be average). Most of the runs are done at an easy pace with one speed workout per week or at least one every other week. Speed can be track (example 8x400m), or a 4-5 mile tempo run at something like 6:45-6:50 per mile. My son was a high school lacrosse and basketball athlete at the time of our Whitney trip and cruised it without training for the hike.
3. I live in FL at a whooping 90' above sea level.
I believe that fitness helps a great deal, but there is no substitute for gradual acclimatization if you have the time to do it. I can definitely feel a huge difference in my performance if I am on a trip that has allowed for a couple of days of acclimatization time rather than just fly in and jump right on the mountain. I have done it both ways and feel like if I don't have the time to acclimatize, I try to stack the odds in my favor by being as fit as I can.
I also subscribe to the theory that AMS is very unpredictable and can strike the fit or the unfit. It can also have vastly different effects on the same person following the same program, on the same mountain at different times.
