Massage & Bodywork

July/August 2012

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education PATHOLOGY PERSPECTIVES | BODY AWARENESS | FUNCTIONAL ANATOMY | SOMATIC RESEARCH Soleus By Christy Cael The soleus is one of two calf muscles that form the bulk of the posterior leg. It lies deep to the gastrocnemius, a large, two-headed muscle that connects the posterior knee and heel. The soleus also attaches to the heel, but is a bit shorter, beginning just below the knee. Together, the gastrocnemius and the soleus form the triceps surae group (triceps meaning "three head," and surae meaning "calf"). The gastrocnemius provides two of the three heads and the other is from the soleus. As these muscles descend the posterior leg, they converge at the Achilles tendon before inserting on the posterior surface of the calcaneus. Together, the gastrocnemius and the soleus plantarflex the ankle, providing force for movements, including jumping, running, standing, and walking. The drive from both muscles pulls through the Achilles tendon and across the bottom of the foot. Differences in function occur because the muscles have different origins. The gastrocnemius originates on the posterior surface of the femoral condyles, while the soleus originates more distally on the proximal tibia and fibula. Both origins are very broad, but the gastrocnemius crosses and is able to act on the knee, while the soleus does not. Functional differences between these muscles are also observed in their physiology. Muscles contain varying ratios of fast-acting and long-lasting muscle fibers. The soleus is typically composed of a higher percentage of long-lasting, or slow-twitch, fibers. Slow-twitch fibers use oxygen to make energy, and remain functional for long periods of time, but are unable to activate quickly for explosive movements. Greater amounts of slow-twitch fibers indicate the muscle functions as a fatigue-resistant, postural muscle. It also means the muscle requires large amounts of oxygen to function optimally. By contrast, the gastrocnemius typically has a higher percentage of fast-acting, fast-twitch fibers. These fibers quickly activate when rapid force is needed, but are unable to sustain activity for more than a few seconds. The gastrocnemius drives explosive movements like jumping, lifting, and sprinting, while the soleus is more active during less intense activities like jogging, standing, and walking. CAEL: Functional Anatomy: A Guide of Musculoskeletal Anatomy for Profs SOLEUS Lippincott Williams & Wilkins Figure 09.31 Dragonfly Media Group 04/07/09 Attachments • Origin: Soleal line and posterior surface of the tibia and posterior head and proximal surface of the fibula • Insertion: Posterior surface of the calcaneus via the Achilles tendon Actions • Plantarflexes the ankle Innervation • Tibial nerve • L5–S2 Celebrate ABMP's 25th anniversary and you may win a refund on your membership. ABMP.com. 49

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