In reply to ffati: load carries = walking uphill with a heavy back.
it was 6 months training - the first 3 was the runs, plus some bike, plus the cross fit, plus some hill walking.
the last 3 months was all about converting the base fitness to specific fitness, hence moving to load carries and building the weight up gradually and doing less bike.
The crossfit was great because it strengthens your back, core and legs which makes load carrying easier. it anaerobic as well as aerobic so helps push your anaerobic threshold up, and they reckon the interval style training increases your number of red blood cells.
I did the Welsh 3000's in 13 hours about 6 weeks before I went. Legs didn't even ache the following day. and They never ached on Denali.