this is a few years old but is still interesting: https://www.outsideonline.com/health/training-performance/ranking-worlds-toughest-outdoor-sports/?utm_campaign=&utm_content=&utm_medium=organic-social&utm_source=Outside%20Magazine-facebook&fbclid=IwAR2NjYSjBsiP8nf1sn6kh_HCkuKpvJvRSTRRPnNKgW_vEx-rMEd6dLm5eH4
what I find more interesting than an objective assessment of elite athletes in various sports is a more practical examination of what happens in real life: people choose a sport based on a variety of personal reasons, and quite often the reasons have nothing to do with genetics or predisposition to being “good” at a sport. eg. Eliot Kipchoge makes marathon running look easy, but he could make 100m track sprinting look very hard. But he did not choose to be a track sprinter.
I race Nordic and Skimo. my race weight is about 30lbs heavier than my competition. and you better believe this makes the uphill ascents in skimo harder for me. look at “climbing specialists” in the TDF, they don’t look like sprinters. I am built like a sprinter but have chosen endurance sports based on passion. that said, I refuse to admit that I may have a harder time moving my mass around, I simply work harder…but I also know that at a certain point I am genetically blocked from being the most elite. I cannot change the laws of physics, but I can choose to ignore them…
so the way I see it: by comparison to other sports, Nordic racing is more like road running racing: consistent pace and sometimes a hill appears. Skimo is more like a Triathlon: intense uphill, transition, hike, transition, downhill, transition, repeat etc. which is harder? ask a bike racer, a track running sprinter, a marathon runner, a nordic racer and a skimo racer if they think their sport is the hardest, they will all say yes. what I can say is that depending on your genetics, desire and training, “hardest or harder” is highly personal. eg. someone genetically built for track sprinting would find the uphill ascents in skimo exceptionally difficult. my other thought, and I have mulled this over many times: for some races or routes, there is a minimum level of “hard”, and the course cannot be completed “easily”..eg Mt Everest. other courses like a Park Run 5K can be completed easily by walking OR very hard by running a 13.x minute time. and finally, Greg Lemond once said ” it never gets easier, you only go faster”. truth.