Fiber orientation, or the direction that a muscle fiber runs, is underrated. People like to mention internal movement, arm length, and leverage, but they will completely neglect that as if fiber orientation doesn’t contribute to internal moment arm length. The internal moment arm length is the perpendicular distance between the joint a muscle acts on and the muscle’s line of pull. So the orientation of the fibers affects the muscle line of pull.
People overlook fiber orientation due to its inconvenience and complexity. Advice given in the gym is to do a certain exercise for this muscle, but two exercises that are similar can target the same muscle, but stress completely different fibers depending on the movement path and joint angles. Fiber orientation also contributes to the amount of leverage that a muscle has; an example of this would be incline vs flat bench. While people like to flat bench, its to mention that the pectoralis major has 3 different sections, such as upper, middle, and lower. When doing a flat bench, the sternal fibers are targeted and pull the arm across the body with an up and down motion, which means the mid chest is the strongest and can do or move more weight. If you move the bench to a 15-30 degree angle, it would target more of your upper chest, and now the press is upward and forward. It matches the downward-angled pull of upper fibbers. The incline bench is better because it targets all three regions, and the shoulders assist less, and it has better fiber alignment.
Progress can still be made without thinking about the contribution of fiber orientation, so people assume that it’s unnecessary, often ignoring or overlooking it, which often leads to uneven development, also known as muscle imbalance, joint pain, stalled progression, or plateauing, or thinking that certain exercises do not work for you. Fiber orientation or muscle fibers are supposed to produce much more force in a specific direction, favor strength over speed, and they typically respond better to certain angles and arm paths.
