Waiter’s walks are an exercise where a load is held in a one arm overhead position while walking. They have a variety of benefits, including:
– Working all of the muscles around the shoulder, including the smaller, stabilizing rotator cuff muscles, to hold the head of the humerus in position.
– The body is loaded asymetrically, so it will work on proper trunk alignment and the endurance of those muscles. The walking will also add some variation to the loading.
– It focuses on upward rotation of the scapula to build stability in the overhead position.
When doing these, focus on a keeping the trunk engaged and neutral without slouching to one side or the other. Put some light external rotation on the shoulder and actively push into the bell to achieve the upward scapula rotation.
During these assymetrical carry exercises I put an emphasis on good mechanics overall from the head to feet. Also short and stable steps are better than flowing steps in order to optimally keep the trunk tight.
Read more about a slightly different type of waiter’s walk on Eric Cressey’s site.