Straight muscle
Musculus rectus
Definition
A straight muscle is a type of skeletal muscle in which the muscle fibres run parallel to each other and in a straight line between the origin and insertion. This arrangement allows the force of contraction to be transmitted efficiently along a single axis, producing direct and controlled linear movement.
Anatomically, straight muscles are often long and strap-like, maintaining a uniform width throughout their length. Their parallel fibre arrangement provides a balance between range of motion and power, making them well-suited for producing precise, coordinated movements.
Examples include rectus abdominis (anterior abdominal wall) and rectus femoris (anterior thigh).
Feature | Fusiform Muscle | Flat Muscle | Straight Muscle |
Shape | Spindle-shaped — thick central belly, tapering at both ends. | Broad, thin, sheet-like with wide attachment areas. | Long and strap-like; uniform width with parallel fibres. |
Fibre arrangement | Long parallel fibres converging toward tendons. | Parallel or oblique fibres spread across a wide surface, often forming aponeuroses. | Parallel fibres that run directly from origin to insertion in a straight line. |
Function | Produces rapid and extensive movement — the long fibres shorten greatly, allowing a large range of motion (e.g., flexion at elbow by biceps brachii). | Generates tension across broad areas — suited for supporting and stabilizing body walls or compressing cavities, rather than producing large joint movements (e.g., abdominal wall compression by external oblique). | Designed for direct, efficient linear movement — fibres act in a straight path, producing controlled flexion or extension with stability (e.g., rectus abdominis flexing the trunk). |
Force generation | Moderate; designed for speed and range, not maximal power. | Moderate; force is spread over a large surface for stability and protection. | Moderate; Force is evenly transmitted along the muscle’s long axis; suited for postural or sustained contractions. |
Range of motion | Wide range, high speed. | Limited range, emphasizes support and protection (greater stability). | Moderate range, more linear and stable. |
Example | Biceps brachii, sartorius | External oblique, pectoralis major, latissimus dorsi. | Rectus abdominis, rectus femoris |
References
Gray, H. (2016) Gray’s anatomy the anatomical basis of clinical practice. 41st edition. Edited by S. Standring. New York: Elsevier.
