Post 3: Synergistic and Biarticular Muscle Action

          I have often assumed that my compound lower body movements and conditioning provided enough volume for my gastroc development. This had proven to be true as I had never experienced deficiencies in performance of the lower posterior leg. However, I recently did some simple barbell calf raises as an assistance exercise (low volume <50 reps, and relatively low intensity) and felt PAIN in the days to follow. This sparked some conversation in the office and foggy recollection from AT classes. What all this essentially boiled down to was some rambling about synergistic and biarticular muscles, as well as length-tension curves and joint angles.

          The gastroc and soleus are synergistic muscles, meaning they are both used to perform essentially the same joint action. In this case, plantarflexion of the ankle (and partially in knee flexion for the gastroc.) I said essentially because there are mitigating factors such as the velocity and joint angle at which the contraction occurs. The lateral and medial heads of the gastroc originate superficially to the knee joint (at the lateral and medial condyles of the femur respectively,) and insert at the achilles (calcaneal) tendon. The soleus however, originates from below the knee (at the flat tendons and condyles of the  tibia and fibula) and also eventually inserts at the achilles.

          Now that we're brushed up on the anatomy, I'll address the problem. I tried some static and dynamic stretches ranging from simple ankle mobility to passive stretching with resistance bands and everything in between, and got no seemingly lasting benefits. I've decided that the reason for my acute discomfort is that I had finally performed fast twitch isolation movement during the calf raises at a nearly straight knee angle. My previous experiences with lower body exercises had allowed ALL synergistic muscles of the legs to contribute to force development in my squats, deadlifts, olympic lifts, etc. and therefore, the fast-twitch fibers of the gastrocs were never entirely isolated. The soleus, hamstrings, quads, and glutes play a greater role due to the acute knee joint angles and lack of strict Type II activation.

Length-Force Relationship

     

          The length-force relationship graph provides visual representation of individual muscle contribution to force production relative to deviation from resting length. The force-velocity graph illustrates how a muscle's ability to produce force is dependent on the rate at which it is lengthened (or shortened.) In addition, when synergistic muscles are engaged simultaneously, the degree to which they contribute depends highly on the joints they cross and the lengths at which they can perform optimally. As previously mentioned, the gastroc crosses both the knee and ankle joint, while the soleus only crosses at the ankle. Because of this, the gastroc was often at lengths too short to provide any serious independent force production, and the soleus would be doing the most work in the calf department.  In my case, the gastrocs were rarely subject (comparitively) to the velocity of contraction, or that isolated range of motion as they were in the calf raises.

Force-Velocity Relationship

          Acting independently, the gastroc was solely responsible for the force production involved in this exercise. For this reason it was exposed to a peak contraction velocity (illustrated by the pink curve on the force-velocity graph) at a joint angle (muscle length - illustrated by the purple line on the length-force relationship) that basically eliminated synergistic contribution from the soleus and other contributory muscle involvement.

-Alex