I have always hated running (or my version of it) and was hoping to do CC5K as my goal this past May. I started trying to mix the elliptical with the treadmill (doing Couch to 5K) and was ok on the elliptical, but having a hard time with my legs on the treadmill. Due to fear of injury, I gave up and just stuck with the elliptical. Anyway, after a few months I worked my way up to about an hour on the elliptical and decided "even if I just jog at 4 MPH or so I should be able to do a 5K in 45 mins." So I got back on the treadmill about 2 weeks before the cruise and was able to do almost 4 miles!!! I was very excited and did the CC5K- Now for that experience (and this is only my own observations)- even with it being completely flat, the CC5K was much harder than running on the treadmill. I think part of that was adrenaline and I didn't pace myself, but after probably 1.5 miles, I needed to stop to walk a bit. I'm sure some of this had to do with the heat/humidity, although I didn't feel like I was feeling that too badly. Also, even with being able to do the elliptical for an hour and run 4 miles on the treadmill, my legs were really hurting for the rest of the cruise- not debilitating, but enough so that every time I sat down I remembered the CC5K. Also, a lot of people said there were a lot of walkers. We had about 40 people my day and I was far and away dead last while not walking all that much. Add to that that I got lost toward the end and added on probably a good quarter mile and I wound up finishing in about 46 minutes (which I didn't think was that bad) but they had already left. I had to get my medal and cert. from guest services All in all though, it was worth it. I still do the elliptical regularly and will start training for our May cruise CC5K in late March or early April.