Zipping along on skis delivers a better heart-pounding workout than running at about the same pace.
Because the sport requires you to push with your lower-body and pull with your upper, recruiting a greater number of muscles.
In fact, a good cross-country ski session can burn more than 12 calories a minute, according to the Compendium of Physical Activities.
That explains why Nordic Skiers consistently collapse in exhaustion at the finish line of Olympic races.
No fresh snow? Look for the new Concept2 SkiErg machine at your gym.