The lateral stretch exercise in Lesson No. 17 (SI, Nov. 4) is a necessary preparation for this week's exercise, the shoulder roll. If you have been successful in adding the earlier maneuver to your 15-minute daily exercise period, you should have no trouble with this more advanced one. The shoulder roll is more than a useful exercise. It is a method of avoiding injury when (and if) you trip over something—a hidden log while hiking or a living room rug.

A Rest your weight on your right knee, shoulde and hand. Use your left toe to help with balance and stretch your right arm along the floor.

B Give a shove with your left leg, relax and let your body roll over your shoulders as in a side somersault, keeping hands in place on the floor.

C You should arrive flat on your back, with your hands still in the first position. Repeat the exercise to the right and then to the left again

THREE PHOTOS