MUSCLES ENGAGED Shoulders The shoulder is the most movable joint in the body. However, it is an unstable joint because of the range of motion allowed. This instability increases the likelihood of joint injury, often leading to a degenerative process in which tissues break down and no longer function well. Triceps Triceps are an often forgotten muscle group. Triceps are located on the opposite side of the biceps at the back of the upper arm. Well strengthened and defined triceps make the arm look bigger and sleeker (reducing the "flabby arm" look). Exercise Instructions Step 1 Hold a light band in both hands. Have your feet approx. shoulder width apart. Step 2 Pull the band up and other your head and touch your backside. Step 3 Pull the band back over to the starting position.