--- title: "Peroneus Longus | Anatomy and Physiology I" description: "Peroneus longus is a lateral leg muscle that everts and plantarflexes the foot while helping support the arch in Anatomy and Physiology I." canonical: "https://fiveable.me/anatomy-physiology/key-terms/peroneus-longus" type: "key-term" subject: "Anatomy and Physiology I" unit: "Unit 8" --- # Peroneus Longus | Anatomy and Physiology I ## Definition The peroneus longus is a muscle in the lateral compartment of the leg that everts and plantarflexes the foot. In Anatomy and Physiology I, it comes up when you study lower-limb movement, ankle stability, and foot arches. ## What It Is The peroneus longus is a long muscle on the outside of the lower leg that crosses the ankle and attaches to the foot. In Anatomy and Physiology I, you usually meet it as one of the lateral compartment muscles that moves the foot and helps steady the ankle during walking, running, and balance tasks. It starts on the head and upper part of the fibula, then runs down the leg behind the lateral malleolus area before reaching the base of the first metatarsal and the medial cuneiform. That path matters because the tendon changes direction around the ankle and pulls on the foot from the outer side, which is what makes its movement pattern so useful for both motion and support. Its main actions are eversion and plantarflexion. Eversion turns the sole outward, and plantarflexion points the foot downward. Those actions are easy to memorize as motion terms, but in the body they work together to control how the foot meets the ground, especially when you shift weight or move on uneven surfaces. The peroneus longus also supports the transverse arch of the foot. Since it inserts near the base of the first metatarsal and medial cuneiform, it helps hold the front of the foot in a stable position. That is why this muscle is not just about movement, it also contributes to maintaining foot structure during standing and gait. A useful way to think about it is as a stabilizer and a mover at the same time. If the muscle is weak, irritated, or injured, you may see ankle instability, trouble with side-to-side control, or a foot that does not handle weight smoothly. In lab images or muscle charts, it is the lateral leg muscle to connect with the fibula, the outer ankle, and the first metatarsal on the medial side of the foot. ## Why It Matters Peroneus longus matters because it connects the lower leg to the mechanics of the foot. In Anatomy and Physiology I, that makes it a useful example of how muscle origin, insertion, and line of pull explain real movement instead of just naming anatomy on a list. It also helps you understand why the fibula matters even though it does not bear as much body weight as the tibia. The fibula gives attachment space for muscles like peroneus longus, and those muscles help control the ankle and foot during gait. When you trace this muscle from the fibula to the base of the first metatarsal, you can see how bones and muscles work together to support arches and balance. This term also shows up in injury discussions. Lateral ankle instability, poor foot mechanics, and overuse problems often make more sense when you can identify the peroneus longus and explain what happens if it cannot evert or stabilize effectively. That kind of reasoning shows up in muscle ID quizzes, movement analysis, and clinical-style questions that ask you to connect structure to function. ## Connections ### Fibula The fibula is the main bony attachment point for the peroneus longus at its origin. If you know where the fibula sits in the lateral leg, it becomes easier to trace why this muscle runs along the outside of the lower limb and how it affects the ankle and foot. The bone gives the muscle a stable anchor for movement. ### Eversion Eversion is one of the main actions of the peroneus longus. When the muscle contracts, it pulls the foot so the sole turns outward, which helps with balance and weight shift. This is a good action term to pair with the muscle because the movement is visible in gait and easy to test on a diagram or movement question. ### Plantarflexion Plantarflexion is the downward pointing motion of the foot, and peroneus longus contributes to it along with other lower leg muscles. In lab or class questions, this helps you separate it from muscles that mainly dorsiflex the foot. It is especially useful when you are tracing how the ankle moves during walking, pushing off, or standing on tiptoe. ### [base of the metatarsal bone](/anatomy-physiology/key-terms/base-of-the-metatarsal-bone) The insertion of peroneus longus near the base of the first metatarsal helps explain its role in arch support. That attachment is not random, it gives the muscle leverage to influence the front of the foot. When you connect this structure to function, the muscle makes more sense as a stabilizer, not just a mover. ### [Distal Tibiofibular Joint](/anatomy-physiology/key-terms/distal-tibiofibular-joint) This joint sits near the ankle region where the lower leg bones meet before the foot begins. It helps frame the anatomy around where the peroneus longus tendon passes on its way into the foot. Knowing the joint location helps you orient the muscle on diagrams and understand the crowded anatomy of the ankle area. ## On the AP Exam A quiz image or muscle-labeling question may show the lateral lower leg and ask you to identify the muscle that everts the foot and helps support the arch. You should connect peroneus longus to its fibular origin, its route past the ankle, and its insertion near the first metatarsal and medial cuneiform. If the question asks about movement, pair the name with eversion and plantarflexion. If it asks about function, mention ankle stability and arch support. In a practical or lab check, it may appear in a diagram alongside the fibula and other lateral compartment muscles, where you have to explain how structure matches action rather than just naming the part. ## peroneus longus vs Peroneus brevis These two lateral leg muscles are easy to mix up because they both help with eversion and sit in the same region. Peroneus longus is the larger, longer muscle and reaches farther into the foot to the base of the first metatarsal and medial cuneiform, while peroneus brevis has a shorter insertion. If you remember the longer muscle reaches farther, the name makes more sense. ## Key Takeaways - Peroneus longus is a lateral leg muscle that helps move and stabilize the foot. - Its main actions are eversion and plantarflexion, which affect how the foot meets the ground. - The muscle originates on the fibula and inserts near the base of the first metatarsal and medial cuneiform. - Its tendon path helps support the arch, so it matters for balance as well as movement. - If it is weak or injured, ankle instability and poor foot control can show up in gait. ## FAQs ### What is peroneus longus in Anatomy and Physiology I? Peroneus longus is a muscle in the lateral compartment of the leg. It everts and plantarflexes the foot and helps support the arches of the foot. In A&P I, you usually study it as part of lower-limb anatomy and muscle action. ### Where does the peroneus longus attach? It originates on the head and upper two-thirds of the fibula. It inserts at the base of the first metatarsal and the medial cuneiform. That insertion helps explain why it can influence both movement and arch support. ### What action does the peroneus longus perform? Its main actions are eversion and plantarflexion. Eversion turns the sole outward, while plantarflexion points the foot downward. Those actions matter during walking, balance, and side-to-side foot control. ### How is peroneus longus different from peroneus brevis? Both muscles are in the lateral leg and help with eversion, so they are commonly confused. Peroneus longus runs farther into the foot and inserts near the first metatarsal and medial cuneiform, which ties it more closely to arch support. Peroneus brevis has a different, shorter insertion. ## Related Study Guides - [8.4 Bones of the Lower Limb ](/anatomy-physiology/unit-8/4-bones-limb/study-guide/72cD9wyZ7AuoW1do) ## About This Document Canonical Fiveable pages are available as Markdown at the same path plus `.md`. - [llms.txt](https://fiveable.me/llms.txt): index of Fiveable's sections and URL patterns - [llms-full.txt](https://fiveable.me/llms-full.txt): complete subject and unit listing - [MCP server](https://fiveable.me/mcp): call Fiveable as tools instead of fetching pages (`https://fiveable.me/api/mcp`) - [MCP server for AP teachers](https://fiveable.me/mcp/teachers): a teacher's classes, assignments and AP-rubric grading (`https://fiveable.me/api/mcp/teacher`) ## Structured Data ```json {"@context":"https://schema.org","@graph":[{"@type":"LearningResource","@id":"https://fiveable.me/anatomy-physiology/key-terms/peroneus-longus#resource","name":"Peroneus Longus | Anatomy and Physiology I","url":"https://fiveable.me/anatomy-physiology/key-terms/peroneus-longus","learningResourceType":"Concept explainer","educationalLevel":"AP® / High School","about":{"@id":"https://fiveable.me/anatomy-physiology/key-terms/peroneus-longus#term"},"audience":{"@type":"EducationalAudience","educationalRole":"student"},"dateModified":"2026-07-03T02:20:41.765Z","isPartOf":{"@type":"Collection","name":"Anatomy and Physiology I Key Terms","url":"https://fiveable.me/anatomy-physiology/key-terms"},"author":{"@type":"Organization","@id":"https://fiveable.me/editorial#content-team","name":"Fiveable Content Team","url":"https://fiveable.me/editorial","parentOrganization":{"@id":"https://fiveable.me/#organization"},"member":[{"@type":"Person","name":"Amanda DoAmaral","sameAs":["https://www.linkedin.com/in/adoamaral"]},{"@type":"Person","name":"Becky Bahr","sameAs":["https://www.linkedin.com/in/becky-bahr-b52743132"]}]},"publisher":{"@type":"Organization","name":"Fiveable","url":"https://fiveable.me"}},{"@type":"DefinedTerm","@id":"https://fiveable.me/anatomy-physiology/key-terms/peroneus-longus#term","name":"peroneus longus","description":"The peroneus longus is a muscle in the lateral compartment of the leg that everts and plantarflexes the foot. 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