What are three facts about the leg?

September 22, 2025 •

4 min read

The human leg is a marvel of evolutionary biology, enabling upright posture and efficient movement. It is responsible for supporting the body's weight and facilitating numerous forms of locomotion, but what are three facts about the leg that might surprise you?

Quick Summary

The femur is the longest and strongest bone, some leg muscles are crucial for blood circulation, and the structure of the human leg has evolved for highly efficient bipedalism.

Key Points

Femur Strength: The femur, or thigh bone, is the longest and strongest bone in the body and can support more than 30 times the body's weight.
Circulatory Aid: The calf muscles function as a "second heart," helping to pump blood from the lower extremities back up to the heart against gravity.
Bipedal Adaptation: Human legs are exceptionally long and powerful, a key evolutionary adaptation for efficient bipedal walking, distinguishing us from other primates.
Knee Joint Structure: The knee is the largest joint in the body, primarily responsible for bearing the body's weight and enabling movement.
Achilles Tendon Power: The Achilles tendon, which connects the calf muscles to the heel bone, is the body's strongest tendon and is crucial for walking and running.
Supporting Arches: The foot arches within the leg structure provide support, absorb shock, and add flexibility to our gait.

A Marvel of Strength: The Femur

One of the most impressive facts about the leg is the immense strength of its largest bone, the femur. Located in the thigh, the femur is not only the longest bone in the human body but also the strongest. It is capable of withstanding forces of 1,800 to 2,500 pounds of compression per square inch, making it tougher than steel of the same weight. This incredible strength is vital, as the femur bears significant load during everyday activities, from standing and walking to running and jumping. Its durability is a testament to the powerful forces it must endure as it connects the hip to the knee, providing a stable foundation for the rest of the body.

The Importance of the Femur in Mobility

Without the femur's robust structure, bipedal locomotion would be impossible. The ball-and-socket hip joint at the top of the femur provides a wide range of motion, while its articulation with the tibia at the knee forms a hinge joint that allows for flexion and extension. This combination of strength and mobility is a key feature of the leg's design, enabling the dynamic movements that define human physical activity.

The Muscular Pump: Aiding Blood Circulation

While the heart is the primary organ for pumping blood, many don't realize the crucial role the leg muscles play in maintaining healthy circulation, particularly in returning blood to the heart. The muscles in the lower leg, especially the gastrocnemius and soleus (the calf muscles), act as a secondary pump. As you walk, run, and move, these muscles contract and relax, squeezing the deep veins in the legs and pushing blood upwards against gravity toward the heart.

The Significance of the Calf Pump

This mechanism, known as the 'calf muscle pump,' is essential for preventing blood from pooling in the lower extremities and for reducing the risk of conditions like deep vein thrombosis (DVT). Individuals who are sedentary for long periods, such as during long flights or hospital stays, are at a higher risk of developing DVT precisely because this muscular pumping action is inactive. Staying active and performing simple leg exercises can significantly benefit circulatory health.

The Bipedal Advantage: Efficient Walking

The evolution of the human leg for bipedalism is a fascinating fact that distinguishes us from most other primates. While other primates can walk upright for short distances, humans are uniquely adapted for sustained bipedal gait. This is a result of several key anatomical changes, including longer legs relative to the trunk and specialized muscles. This adaptation allows for more efficient locomotion, requiring less energy to walk than a quadrupedal gait would. It has also freed our hands for tasks like carrying objects, using tools, and gesturing.

The Anatomy of Efficient Locomotion

This bipedal efficiency is supported by several anatomical features:

The double S-shaped curve of the spine, which acts as a shock absorber.
The powerful gluteal muscles that stabilize the trunk during walking.
The arches in the foot, which act as a flexible lever and absorb shock.

This intricate system of bones, muscles, and joints has made sustained walking and running possible for our species, contributing significantly to our survival and development.

Leg Health: A Comparative Look

To further understand the importance of leg health, consider this comparison between active and sedentary lifestyles.


Feature	Active Lifestyle	Sedentary Lifestyle
Circulatory Health	Enhanced venous return; efficient blood flow; reduced risk of DVT.	Stagnant blood flow; reduced effectiveness of the calf muscle pump; increased risk of blood clots.
Muscle Strength	Strong quadriceps, hamstrings, and calf muscles; improved stability and endurance.	Muscle atrophy; decreased strength; higher risk of strains and imbalances.
Joint Function	Healthy cartilage and lubricated joints; robust ligaments; lower risk of degenerative conditions.	Stiff, underused joints; potential for cartilage wear and early onset arthritis.
Overall Mobility	High mobility and flexibility; ability to perform complex movements with ease.	Decreased range of motion; limited flexibility; potential for mobility impairments.

Caring for Your Legs

Given these facts, it's clear why taking care of your legs is so important for overall health and mobility. Regular exercise, including walking, cycling, and strength training, is vital for maintaining muscle strength and promoting healthy circulation. Stretching can help maintain flexibility and range of motion, reducing the risk of injury.

For more detailed information on leg health and exercises, consult the Health Encyclopedia on the Hospital for Special Surgery website. This resource provides authoritative guidance on various conditions and treatments related to the musculoskeletal system, including the legs.

Conclusion

From the immense strength of the femur to the circulatory support from the calf muscles and the evolutionary design for bipedal efficiency, the human leg is a complex and highly effective part of our anatomy. Understanding these facts highlights the importance of keeping our legs healthy and active to support our overall well-being throughout our lives.

Frequently Asked Questions

The femur is the strongest bone because it must bear the significant weight of the upper body and withstand the immense forces generated during movement. Its dense composition allows it to support up to 30 times the body's weight.

When you walk or move, the contraction and relaxation of your calf muscles squeeze the deep veins in your legs, acting like a pump. This action helps push deoxygenated blood back up to the heart, assisting the circulatory system.

Human legs are uniquely adapted for highly efficient bipedalism, meaning we can walk upright for long distances with less energy expenditure than other primates. Key adaptations include longer legs relative to our torso and specialized muscles.

The knee joint is the largest joint in the body and connects the femur to the tibia. Its primary functions are to bear weight and to allow for the bending and straightening of the leg, which is essential for walking, running, and jumping.

The Achilles tendon is the body's largest and strongest tendon, connecting your calf muscles to your heel bone. It is critical for ankle movement and for pushing off the ground when walking, running, and jumping.

The arches of the foot are a crucial part of the leg's structure, acting as both a shock absorber and a flexible lever. They help distribute the weight of the body evenly across the foot and provide the springiness needed for an efficient gait.

A sedentary lifestyle can negatively impact leg health by weakening muscles, reducing circulatory function, and increasing the risk of conditions like deep vein thrombosis (DVT). It's important to incorporate regular movement to keep your legs healthy.