I did Half Dome about 10 yrs ago before I was really into hiking. I did it with no training and up until 2011, it was still the hardest hike I had ever done.
In 2011 someone convinced me to hike Whitney with them. We trained all summer and I was still surprised at how difficult it was, mainly due to the AMS factor. I didn't really enjoy Half Dome all that much (I didn't like the cables), but some day I would like to do it again just to see how I'd rate it's difficulty now that I have more experience hiking.
Last year I invited two of my 'halfdome buddies' to fly out from the east coast to do Whitney with me. Here is a portion of an email I sent to them in regards to training:
We're less 11 than weeks out from the Whitney hike and it's time to start thinking about training.
Most of the things I've read about training for Whitney have stressed quality of training over quantity. Shorter hikes with more elevation gain seem to be more beneficial than longer hikes without much climbing. That being said, here are a few benchmarks that can help you prepare for a summit attempt:
1. a hike with at least 5000 ft of elevation gain or a workout with 5000 ft of continuous climbing
2. a hike that's at least 15 miles long (20 miles is better)
3. a hike that takes 10+ hours to complete
For those of us that live in Southern California, a hike up San Gorgonio will satisfy all three benchmarks. For those travelling from the east coast, #1 will be very difficult to fulfill. This sounds like a horrible way to spend an afternoon, but here is a suggestion I got from a man that lives in Atlanta, but hikes Whitney at least once per year:
"I hit the gym about a week out and put in 6000 feet of gain on a treadmill set at 15 degrees, just to make sure my legs can handle it in one day. I've been hiking and climbing western mountains for about 10 years, and the biggest problem in training here in the east is the inability to get sustained gains in these low mountains. Your legs always get a downhill break after no more than 2000 feet, which is definitely not the case in the Sierras. The treadmill always tells me how ready I am."
This could also be done on a stair climber (my preference if I were going to torture myself). For reference, some googling shows that 100 flights is roughly equivalent to a 1000 ft of elevation gain.
While #1 is about leg strength/conditioning, numbers 2 and 3 are helpful in preparing your feet for summit day. For those of us that sit at a desk all day, spending an entire day walking can be very painful. On summit day you will need to be prepared to hike ~18 miles, which will likely take 12 hours or more. Another thing to consider during training is pack weight. Overnight packs will probably weigh 30-40 lbs. On summit day, our packs shouldn't weigh more than 20-25 lbs. While training for a big hike, I tend to carry a pack that has a weight greater or equal to what I'll carry on the big hike. With this in mind, I would try get in a 5 mile hike with a 40 lb pack and do the majority of your training while carrying 20+ lbs.
Reaching these benchmarks is not necessary - you may be able to summit without doing them and doing them doesn't guarantee that you'll summit. If you do the training necessary to reach them though, I do believe that your hike will be more enjoyable.
Both the guys from the east coast were able to summit. One of them said it was tougher than any of the marathons he's done. The other said that Half Dome would 'be a cake-walk' compared to Mt. Whitney.
