Sri Chinmoy: If your legs get tired from standing all day, there are two exercises that are very good to strengthen them. One exercise develops the knee muscles. You sit on the floor with one leg straight, and the other leg bent with the knee up, both hands on your hips. Then you switch, bending the straight leg and straightening the bent leg. Then keep switching.
The other exercise is to do a deep knee bend on one leg, with the other leg out in front of you, then to stand up again, still keeping one leg in front of you. First you do it on your flat foot, then on your toe. If you can do it three or four times, your legs will have tremendous strength from top to bottom.