It might be surprising that the Sanskrit name Utkatasana is sometimes translated as Fierce Seat or Powerful Pose. The asana looks fairly straightforward and simple—you bend the knees as if preparing to sit on a chair. It looks so much like someone sitting on an imaginary chair that it's commonly called Chair Pose.
But rather than let you relax back into a La-Z-Boy, Utkatasana requires you to support yourself in a standing squat. This action engages the muscles of your legs and back—and is arguably the single best movement for strengthening the thighs, both the quadriceps and the hamstrings, as well as the erector spinae muscles in the back. Leg-strengthening squats are workout staples at the gym, where people often do them while holding weights. Utkatasana is similarly strengthening but should generate less wear and tear on your joints over the long haul.