Final answer:
Muscles with fascicles aligned along the long axis have a parallel arrangement, permitting significant extension and flexion.
Step-by-step explanation:
A muscle with a pattern of fascicles running along the long axis of the muscle is described as having a parallel fascicle arrangement. In this configuration, the muscle fibers and fascicles extend in the same direction as the long axis of the muscle, which allows for a high degree of extensibility and flexibility during muscle contraction and trunk flexion, such as seen in muscles like the rectus abdominis. This arrangement contrasts with others like the transversus abdominis, which has fascicles arranged transversely around the abdomen, and the trapezius, which helps to stabilize the upper part of the back with a different fascicle arrangement.