Fiber direction is the grain of a muscle, which strokes follow to lengthen and cross to loosen.
Along the grain, a slow stroke asks the muscle to take length. Across it, a short stroke asks packed fibers to slide. In 📝Deep Tissue Massage knowing the grain is how the hands choose the stroke, not a diagnosis of a tear along a line. Working against anatomy by accident is how a pass becomes painful without getting deeper.
Clients do not need the anatomy name. They feel the difference as a stroke that makes sense versus a stroke that snags. Sharp or shooting pain is a stop.