Snowshoeing on unpacked snow, even at a sluggish 3 mph, can expend twice the energy as walking on a treadmill. You'll hit your cardiovascular system a whole new way if you do your shoeing at high altitude, where, over time, your body will produce more red blood cells.
Not only does it demand power from your quads, hams, glutes, and calves, snowshoeing also taxes the stabilizer muscles (the adductors and abductors) on the inside and outside of the thighs as you work to balance yourself on the shifting surface of the snow.
Amp It Up
Ryan Alford, publisher of Snowshoe Magazine, recommends alternating five minutes of shoeing on the more cooperative harder-packed, on-trail snow with five minutes on unpacked off-trail snow. The softer snow is where your body has to work the hardest, especially when you have to negotiate obstacles in your path, while the hard-packed snow offers a chance to recover a bit. Each week tack on an additional on-trail/off-trail interval; if it all feels too easy, challenge yourself whenever possible with off-trail inclines.