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Psoas major Next Issue: Using Push and Pull in Massage Line of pull Exploring Technique Post-Isometric Stretch for the Tibialis Anterior 3 The vertical line of pull of the psoas major has a stabilizing effect. Muscles that exert a line of pull around a corner act as anatomical pulleys, changing the direction of muscular pull and/or increasing its magnitude of force. The tendon of the tibialis posterior muscle wraps around the medial malleolus of the ankle, shifting its pull from a vertical to a horizontal force that initially lifts the medial arch and eventually plantarflexes the ankle and inverts the foot. STABILIZATION AND JOINT-MOVEMENT PULLS The closer the line of a muscle's pull is to the axis of joint motion, the greater its stabilizing effect. This occurs with many vertically oriented muscles situated along the spine. A light contraction of the psoas major exerts a stabilizing force on the lumbar spine and hip, drawing the vertebral bodies together and pulling the femoral head into its socket (Image 3). The psoas major reaches its maximum joint-movement force at 90 degrees of hip flexion, either pulling the hip into deeper flexion or the lumbar vertebrae into extension. Here are a few more tips for assessing joint actions along lines of muscular pull: This two-step muscle energy technique can be done with any muscle. Begin by figuring out the joint actions of the tibialis anterior, tracing its line of pull from origin to insertion. 1. Since the action of the tibialis anterior is dorsiflexion with inversion, passively move the ankle into this position. Instruct your partner to resist while you lightly pull the ankle in the direction of the antagonist pattern, plantarflexion with eversion. Hold for several seconds. 2. Have your partner relax as you release the hold, then slowly stretch the ankle in the direction of the antagonist pattern— plantarflexion and eversion—until your partner feels the tibialis anterior stretch (make sure to ask). Hold the stretch for several seconds, then release. • Hold the origin and insertion of the target muscle, then shorten the distance between your hands, moving the joint under it. • When assessing a muscle with multiple lines of pull, assess each line one at a time. • When assessing a limb muscle that acts on two or more joints, assess the action at each joint separately. Mary Ann Foster is the author of Therapeutic Kinesiology: Musculoskeletal Systems, Palpation, and Body Mechanics (Pearson Publishing, 2013). She can be contacted at mafoster@somatic-patterning.com. Resisted movement of the tibialis anterior. Images courtesy of Pearson. www.abmp.com. See what benefits await you. 109