Muscle Architecture and Eccentric Versus Concentric Remodeling

Muscle architecture is the arrangement of fibers relative to the line of force generation. With B-mode ultrasound aligned to the fascicle plane, you can measure muscle thickness, pennation angle and fascicle length. These feed into physiological cross-sectional area, which cuts all fibers at right angles and relates to maximal force. A larger PCSA gives more force, while longer fibers widen the force-length range and may allow faster contraction. Eccentric and concentric contractions generate force differently; in eccentric work, titin may bind to actin and add passive tension. On a leg press, fascicles shorten and pennation rises in the concentric phase, but they lengthen when lowering the load. After 10 weeks of each type of training, muscle volume increased similarly, but concentric training raised pennation angle more and eccentric training increased fascicle length more. Martino stresses that muscle is not just contractile tissue. The extracellular matrix transmits force actively and passively, so an eccentric contraction stretches a system more like a rope than an elastic band, and connective tissue adapts too.