The most unlikely aid to your leg exercise? Bed pillows--they can make your legs stronger. When men attempted single-leg squats while standing on a cushy surface, their hips and leg muscles worked up to 13 percent harder, report Mayo Clinic researchers.

It's a tricky maneuver, however, because you can easily lose your balance. If you can do three sets of 10 wobble-free single-leg squats while standing on a hard floor, bring on the pillow.