I've been doing CrossFit- style workouts for the last couple of years. We do a lot of heavy Olympic weight lifting as well as short, high intensity cardio (box jumps, burpies, 100m sprints, etc.).
In addition to general improvements in all-around fitness and strength, I feel like I've also seen an improvement in my hiking fitness. I can hike farther, faster and if necessary, carry heavier loads, all with less effort. In addition to being stronger, the cardio work seems to provide noticeable benefits; my heart rate is lower, breathing stays more regular and I just plain old feel better while pushing a 3.5- 4mph hiking pace.
I've recently begun training for a marathon distance trail run as part of a longer triathlon and with very little of a running base to start from, I'm up to 1/2 marathon distance a couple of weeks into my training and feeling good and strong. I credit the gym workouts.