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technique @WORK | THE SCIENCE OF MOVEMENT | ENERGY WORK | MYOFASCIAL TECHNIQUES Assessing Joint Actions Along Lines of Muscular Pull By Mary Ann Foster A number of massage techniques require Sartorius muscle an understanding of what actions a muscle produces at a given joint. These techniques include passive stretching and resisted movement assessments, as well as muscle energy techniques such as post-isometric stretching. This knowledge is also essential for isolating the contraction of a specific muscle during palpation, when we direct our clients on how to contract that muscle. If you know the origin and insertion of a muscle, you can assess its joint action(s): 1.Draw a line between the origin and insertion of a muscle on the joint it crosses. This is its line of pull— the direction a muscular force exerts on a joint. 2.Bend and/or rotate the joint under the muscle you just traced in the direction of its line of pull. This movement shows the joint action(s) of that muscle. Figuring out a joint action with these two steps is simple with a uniarticular (one joint) muscle crossing the center of a hinge joint. For example, the vastus intermedius crosses the midline of the knee; therefore, its line of pull produces one action: extension. When a muscle crosses the side of a joint, it exerts a rotational pull. The gluteus maximus arises on the posterior and lateral side of the coxofemoral joint, so its line of pull produces hip extension and lateral rotation. DIAGONAL AND MULTIPLE LINES OF PULL Figuring out joint actions becomes somewhat more complex when a muscle has a diagonal line of pull and/or is biarticular (acting on two joints). Take, for example, the sartorius. It runs from the lateral side of the pelvis to the medial side of the knee and produces a diagonal force that simultaneously flexes and laterally rotates the hip (Image 1). Depending on activity in its synergists or antagonists, the sartorius can also abduct the hip. Since the sartorius inserts below the medial side of the knee, it also medially rotates the knee, but only from a flexed-knee position. 108 massage & bodywork november/december 2013 1 2 Diagonal line of pull: the sartorius. Multiple lines of pull: the trapezius. Muscles with broad attachments have multiple lines of pull and multifaceted actions. A classic example is the trapezius, whose upper, middle, and lower parts respectively elevate, retract, and depress the scapula. For instance, during rock-climbing, the lines of pull produced by the trapezius shift like spokes on a turning wheel, progressively moving through its fan of fibers as the climber abducts the arm in an upward or downward arc (Image 2).