Human leg

Key takeaways

Human leg belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Human leg to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Human leg from memory before moving on to harder problems.

Reference excerpt

The human leg is the lower limb of the human body, including the thigh, knee, lower leg, ankle, foot, or sometimes even the hip or buttock region. There are thirty bones in each leg. The major bones are the femur (thigh bone), tibia (shinbone), and adjacent fibula. The part of the leg between the hip and the knee is called the thigh. The part between the knee and the ankle is called the lower leg, shank, crus, or in anatomy simply the leg. The lower leg includes the shin in the front and the calf at the back. Legs are used for standing, many forms of human movement, recreation such as dancing, and constitute a significant portion of a person's mass. Evolution has led to the human leg's development into a mechanism specifically adapted for efficient bipedal gait. While the capacity to walk upright is not unique to humans, other primates can only achieve this for short periods and at a great expenditure of energy. In humans, female legs generally have greater hip anteversion and tibiofemoral angles, while male legs have longer femur and tibial lengths.

Structure

In human anatomy, the lower leg or crus (or shank) is the part of the lower limb that lies between the knee and the ankle. In the lower leg, the calf is the back portion, and the tibia or shinbone together with the smaller fibula make up the shin, the front of the lower leg. Anatomists restrict the term leg to this use, rather than to the entire lower limb. The thigh is between the hip and knee and makes up the rest of the lower limb. The term lower limb or lower extremity is commonly used to describe all of the leg.

Evolution has provided the human body with two distinct features: the specialization of the upper limb for visually guided manipulation and the lower limb's development into a mechanism specifically adapted for an efficient bipedal gait. While the capacity to walk upright is not unique to humans, other primates can only achieve this for short periods and at a great expenditure of energy. The human adaption to bipedalism has also affected the location of the body's center of gravity, the reorganization of internal organs, and the form and biomechanism of the trunk. In humans, the double S-shaped vertebral column acts as a great shock-absorber which shifts the weight from the trunk over the load-bearing surface of the feet. The human legs are exceptionally long and powerful as a result of their exclusive specialization for support and locomotion—in orangutans the leg length is 111% of the trunk; in chimpanzees 128%, and in humans 171%. Many of the leg's muscles are also adapted to bipedalism, most substantially the gluteal muscles, the extensors of the knee joint, and the calf muscles.

Bones

The major bones of the leg are the femur (thigh bone), tibia (shin bone), and adjacent fibula, which are all long bones. The patella (kneecap) is a sesamoid bone (the largest in the body) in front of the knee. Most of the leg skeleton has bony prominences and margins that can be palpated, and some serve as anatomical landmarks that define the extent of the leg. These landmarks are the anterior superior iliac spine, the greater trochanter, the superior margin of the medial condyle of tibia, and the medial malleolus. Notable exceptions to palpation are the hip joint, and the neck and body, or shaft of the femur. Usually, the large joints of the lower limb are aligned in a straight line, which represents the mechanical longitudinal axis of the leg, the Mikulicz line. This line stretches from the hip joint (or more precisely the head of the femur), through the knee joint (the intercondylar eminence of the tibia), and down to the center of the ankle (the ankle mortise, the fork-like grip between the medial and lateral malleoli). In the tibial shaft, the mechanical and anatomical axes coincide, but in the femoral shaft they diverge 6°, resulting in the femorotibial angle of 174° in a leg with normal axial alignment. A leg is considered straight when, with the feet brought together, both the medial malleoli of the ankle and the medial condyles of the knee are touching. Divergence from the normal femorotibial angle is called genu varum if the center of the knee joint is lateral to the mechanical axis (intermalleolar distance exceeds 3 cm), and genu valgum if it is medial to the mechanical axis (intercondylar distance exceeds 5 cm). These conditions impose unbalanced loads on the joints and stretching of either the thigh's adductors and abductors. The angle of inclination formed between the neck and shaft of the femur (collodiaphysial angle) varies with age—about 150° in the newborn, it gradually decreases to 126–128° in adults, to reach 120° in old age. Pathological changes in this angle result in abnormal posture of the leg: a small angle produces coxa vara and a large angle coxa valga; the latter is usually combined with genu varum, and coxa vara leads genu valgum. Additionally, a line drawn through the femoral neck superimposed on a line drawn through the femoral condyles forms an angle, the torsion angle, which makes it possible for flexion movements of the hip joint to be transposed into rotary movements of the femoral head. Abnormally increased torsion angles result in a limb turned inward and a decreased angle in a limb turned outward; both cases resulting in a reduced range of a person's mobility.

Muscles

Hip

There are several ways of classifying the muscles of the hip:

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Human leg

Start with the simplest possible case. Write down what Human leg claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Human leg before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Human leg ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Human leg

In research: Human leg appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Human leg in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Human leg is common in secondary-school and first-year university syllabi. It links to neighbouring topics Animal locomotion, Lower limb anatomy, so understanding it makes those chapters shorter.
In everyday life: Look for Human leg outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Human leg in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Human leg means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Human leg out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Human leg in simple terms?

The human leg is the lower limb of the human body, including the thigh, knee, lower leg, ankle, foot, or sometimes even the hip or buttock region. There are thirty bones in each leg.

Why does Human leg matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Human leg?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Human leg.