Having done both the Battenkill road race and the Lake Placid Loppet multiple times now, I thought comparing them might be interesting. They both entail similar amounts of climbing, around 4000ft. Masters winning times between the two events are comparable, around 2.5hrs. Battenkill covers 55 miles of dirt and paved roads while Lake Placid covers 31 miles on snow. So one would think the suffer factor should be nearly equal between these two events, right? Not even close.
In a ski race like Lake Placid, there is no sitting in. There are only fleeting instances where you might derive some draft benefit. It is pretty much a 2.5-3hr individual time-trial. Battenkill on the other hand, has lengthy flat, open sections where one can reduce their workload sitting in the pack by 40%. Sure, it's each man for himself on the climbs, but more than half the race you have the option to reduce your effort to conversation pace. No such deal skiing.
Skiing is weight bearing, riding is weight supported. Any weight bearing activity automatically drives up your heart rate. More muscle mass is activated to keep your balance. On the bike, coasting really doesn't require any energy expenditure beyond base metabolic rate. I have coasted down long hills on the bike an saw my HR drop into the 50's. I'm lucky if I can see below 110bpm gliding down a long hill on skis.
XC skiing brings all of your major muscle groups into play at once - legs, core, upper body and arms. This places huge demand on your cardio system. While cycling utilizes your biggest muscle groups, a relatively few muscles are used.
When you add all this up, you can hold a much higher HR over three hours skiing than you can three hours cycling. Does HR matter? Not really. Skiing is a sure fire way to achieve maximum endorphin buzz. You will feel it's sedating effects for days afterwards. No expensive controlled substances needed. A fix you can get in 5-6hrs riding can be had in just 3hrs skiing. I used to call XC skiing cross-training. Not anymore. It's all part of the package deal of doing active things you enjoy. It has been quipped that cross-training is for people who hate bicycles. Heading out to one of the many mountain XC ski centers for a three hour ski is really no different than heading over to your favorite riding trails. No cars, few people, lots of challenging terrain, and the sense of being fully satiated when you're done. Skiing is much simpler, really, even than riding a singlespeed. There are very few moving parts to skis. It's just you and Mother Nature. There's been way too much whining lately about the severity of this winter, trainers suck, salt ate my bicycle type crap. Do something that doesn't suck. Take advantage of an epic winter. I may start whining when spring arrives and I can't ski anymore. I don't hate my bicycle either.