Leg Muscles of The Human Body

The human body is an amazing machine, with intricate design and complex functioning. Among its many parts, the leg muscles play a crucial role in our mobility and stability. In this comprehensive article, we will explore the fascinating world of leg muscles, delving into the details of each muscle. Our journey will take us through the origins and insertions of these muscles, revealing their unique starting and ending points that allow them to function effectively.

In this article, we will examine the individual functions of muscles and how they work in conjunction with the rest of the body. We will also explore their innervation, which is the nerve connections that make these muscles work. Whether you are an aspiring anatomist, a fitness enthusiast, or simply curious about how your body functions, this article will provide you with detailed and insightful information about the muscles that power our movements.

Defining Terms

Origin – The fixed attachment point of a muscle. This is typically the end of the muscle that attaches to the more stationary bone in a pair of bones being moved by that muscle. The origin is generally proximal, meaning closer to the center of the body, or on the more stable part of the skeletal structure.

 

Insertion – The insertion point of a muscle is where it attaches to the bone and is the part that moves during muscle contraction. This part of the muscle is usually located far from the center of the body, and moves towards the muscle’s origin when it contracts. Understanding the insertion point is important in determining a muscle’s function in movement and leverage, as it influences the direction and force of the movement produced by the muscle contraction.

 

Isolated Function – The term “isolated function” refers to the specific action a muscle performs when it contracts independently, without the influence of other muscles. Understanding this concept is crucial for comprehending the primary role of each muscle in movement, as it highlights the muscle’s unique ability to produce a particular movement at a joint. The study of isolated functions is often used to understand muscle imbalances, rehabilitation needs, and design targeted exercises for strengthening or stretching a specific muscle.

 

Integrated Function – The coordinated action of muscles is crucial during complex movements and requires them to work in concert with other muscles and body systems. Isolated function, which focuses on a muscle acting alone, is not enough to fully understand bodily movements. Integrated function, on the other hand, emphasizes how muscles function together in groups, providing a more holistic view of bodily movements. This concept is essential to comprehend how muscles contribute to overall body mechanics, stability, and efficiency during everyday activities and sports.

 

Innervation – the supply of nerves to a muscle, which enables the muscle to receive and respond to neural signals. This connection is crucial for muscle activation and control, as it allows the nervous system to regulate muscle contractions, both voluntary and involuntary. Innervation is a key aspect in understanding how muscles function, their responsiveness to stimuli, and their role in movement and sensation.

 

Concentric – refers to a type of muscle contraction in which the muscle fibers shorten as they contract. This occurs when a muscle generates enough force to overcome resistance, resulting in the movement of body parts towards each other. A common example of a concentric contraction is the upward movement during a bicep curl, where the bicep muscle shortens to lift the weight. Concentric contractions are integral to many types of physical activities and exercises, playing a key role in building muscle strength and movement.

 

Eccentric – refers to a type of muscle contraction where the muscle lengthens while under tension. This occurs when a muscle gradually controls or resists the movement caused by an external force, like gravity. Eccentric contractions are often associated with controlled lowering or decelerating actions, such as lowering a weight during a bicep curl or descending stairs. They play a crucial role in activities requiring controlled movements and are significant in muscle strengthening and injury prevention.

 

Isometric – refers to a type of muscle contraction where the muscle generates force without changing its length. During isometric exercises, the muscle neither shortens (as in concentric contractions) nor lengthens (as in eccentric contractions), but tension is still produced. Common examples include holding a plank position or maintaining a squat. Isometric contractions are essential for stabilizing joints and maintaining posture, and they are often used in rehabilitation and strength training programs.

 

Anterior Tibialis

Origin

The lateral condyle and the upper two-thirds of the outer surface of the tibia.

Insertion

The base of the first metatarsal and the medial and plantar aspects of the medial cuneiform.

Isolated Function

Concentric Action – Ankle dorsiflexion and inversion

 

Integrated Function

Eccentric Action – Ankle plantar flexion and eversion

Isometric Action – Stabilizes the arch of the foot

Innervation

Deep fibular (peroneal) nerve

Posterior Tibialis

Origin

Proximal two-thirds of posterior surface of the tibia and fibula

Insertion

Every tarsal bone (navicular, cuneiform, and cuboid) but the talus plus the bases of the second through the fourth metatarsal bones – the main insertion is on the navicular tuberosity and the medial cuneiform bone

Isolated Function

Concentric Action – Ankle plantar flexion and inversion of the foot

Isometric Action – Stabilizes the arch of the foot

Integrated Function

Eccentric Action – Ankle dorsiflexion and eversion

 

Innervation

Tibial nerve

Soleus

Origin

Posterior surface of the fibular head and proximal one-third of its shaft and from the posterior side of the tibia

Insertion

Calcaneus via the Achilles tendon

Isolated Function

Concentric Action – Accelerates plantar flexion

 

Integrated Function

Eccentric Action – Decelerates ankle dorsiflexion

Isometric Action – Stabilizes the foot and ankle

 

Innervation

Tibial nerve

Gastrocnemius

Origin

Posterior aspect of the lateral and medial femoral condyles

Insertion

Calcaneus via the Achilles tendon

 

Isolated Function

Concentric Action – Accelerates plantar flexion

 

Integrated Function

Eccentric Action – Decelerates ankle dorsiflexion

Isometric Action – Isometrically stabilizes the foot and ankle complex

 

Innervation

Tibial nerve

Fibularis (Peroneus) Longus

Origin

Lateral condyle of tibia, head and proximal two-thirds of the lateral surface of the fibula

 

Insertion

Lateral surface of the medial cuneiform and lateral side of the base of the first metatarsal

 

Isolated Function

Concentric Action – Plantar flexes and everts the foot

 

Integrated Function

Eccentric Action – Decelerates ankle dorsiflexion

Isometric Action – Stabilizes the foot and ankle complex

 

Innervation

Superficial fibular (peroneal) nerve

Biceps Femoris (Long Head)

Origin

Ischial tuberosity of the pelvis, part of the sacrotuberous ligament

 

Insertion

Head of the fibula

 

Isolated Function

Concentric Action – Accelerates knee flexion, hip extension, and tibial external rotation

 

Integrated Function

Eccentric Action – Decelerates knee extension, hip flexion, and tibial internal rotation

Innervation

Tibial nerve

Biceps Femoris (Short Head)

Origin

Lower one-third of the posterior aspect of the femur

 

Insertion

Head of the fibula

 

Isolated Function

Concentric Action – Accelerates knee flexion and tibial external rotation

 

Integrated Function

Eccentric Action – Decelerates knee extension and tibia internal rotation

Isometric Action – Stabilizes the knee

 

Innervation

Common fibular (peroneal) nerve

Semimembranosus

Origin

Ischial tuberosity of the pelvis

 

Insertion

Posterior aspect of the medial tibial condyle of the tibia

 

Isolated Function

Concentric Action – Accelerates knee flexion, hip extension, and tibial internal rotation

 

Integrated Function

Eccentric Action – Decelerates knee extension, hip flexion, and tibial external rotation

 

Innervation

Tibial nerve

Semitendinosus

Origin

Ischial tuberosity of the pelvis and part of the sacrotuberous ligament

 

Insertion

Proximal aspect of the medial tibial condyle of the tibia (pes anserine)

 

Isolated Function

Concentric Action – Accelerates knee flexion, hip extension, and tibial internal rotation

 

Integrated Function

Eccentric Action – Decelerates knee extension, hip flexion, and tibial external rotation

Isometric Action – Stabilizes the Lumbo-Pelvic-Hip Complex

 

Innervation

Tibial nerve

Vastus Lateralis

Origin

Anterior and inferior border of the greater trochanter, lateral region of the gluteal tuberosity, and lateral lip of the linea aspera of the femur

 

Insertion

Base of the patella and tibial tuberosity of the tibia

 

Isolated Function

Concentric Action – Accelerates knee extension

 

Integrated Function

Eccentric Action – Decelerates knee flexion

Isometric Action – Stabilizes the knee

 

Innervation

Femoral nerve

Vastus Medialis

Origin

The lower region of intertrochanteric line, the medial lip of linea aspera, and proximal medial supracondylar line of the femur

 

Insertion

The base of the patella and tibial tuberosity of the tibia

 

Isolated Function

Concentric Action – Accelerates knee extension

 

Integrated Function

Eccentric Action – Decelerates knee extension

Isometric Action – Stabilizes the knee

 

Innervation

Femoral nerve

Vastus Intermedius

Origin

Anterior-lateral regions of the upper two-thirds of the femur

 

Insertion

The base of the patella and tibial tuberosity of the tibia

 

Isolated Function

Concentric Action – Accelerates knee extension

 

Integrated Function

Eccentric Action – Decelerates knee flexion

Isometric Action – Stabilizes the knee

 

Innervation

Femoral nerve

Rectus Femoris

Origin

Anterior-inferior iliac spine of the pelvis

 

Insertion

The base of the patella and tibial tuberosity of the tibia

 

Isolated Function

Concentric Action – Accelerates knee extension and hip flexion

 

Integrated Function

Eccentric Action – Decelerates knee flexion and hip extension

Isometric Action – Stabilizes the Lumbo-Pelvic-Hip Complex and knee

 

Innervation

Femoral nerve

Conclusion

References

National Academy of Sports Medicine. NASM Essentials of Personal Training. Jones and Bartlett Publishers; 7th edition (Jan. 4, 2021) 

National Academy of Sports Medicine. NASM Essentials of Corrective Exercise Training. Jones and Bartlett Publishers; 2nd edition (Jan. 13, 2021)