Biomechanics
Biomechanics is the study of how the body moves, using the physical laws of force and motion. It views bones as levers, joints as fulcrums, and muscles as engines that generate force, explaining how we walk, run, lift objects, and sit. If you have ever wondered why some movements feel heavy and others feel light, this is the field that offers answers.
What kind of field is it?
The word biomechanics combines “bio,” meaning life, with “mechanics.” Just as an architect calculates how a building withstands loads, biomechanics examines which forces act where when the body moves.
The scientific study of body movement has a long history. In the 17th century, the Italian scholar Borelli wrote a book explaining animal movement through the principles of levers and forces. Today, biomechanics is widely used to improve sports performance, support rehabilitation and orthotic design, improve work environments, and design products such as shoes and chairs. Both filming and analyzing an athlete’s movements and determining the angle of an office chair fall within its scope.
How does it view the body?
Biomechanics looks at the body in the following way.
- Bones are rigid rods that transmit force.
- Joints are the fulcrums around which those rods rotate.
- Muscles are engines that generate force to pull on the rods.
- Gravity and the ground exert forces from outside the body. When you push against the ground, it pushes back with an equal amount of force. This is called ground reaction force.
This perspective makes movements easier to explain. When you bend your elbow to lift an object, the farther your hand is from your elbow, the more force your muscles must generate, even for the same weight. This is because a weight farther from the fulcrum produces a greater turning force (torque). This is the principle behind levers and moment arms. The same principle explains why a heavy load feels much lighter when you hold it close to your body.
Two main branches
Biomechanics can be broadly divided into two questions.
- Kinematics — Examines “how did it move?” It records only changes in position, velocity, and angle, without considering forces. An example is how many degrees the knee bends during walking.
- Kinetics — Examines “why did it move that way?” It deals with the forces and torques that produced the movement. An example is how much force the thigh muscles had to generate as the knee bent.
Looking at both lets us understand the form of a movement and the forces behind it. The field that examines the movement of an individual joint in detail is arthrokinematics.
Where it appears in everyday life
- Walking and running — With each step, the foot contacts the ground, the body moves forward over it, and the foot leaves the ground. The gait cycle breaks this sequence into phases, while running has its own running gait cycle. The forces from the ground are much greater during running than walking, making footwear and stride length important.
- Standing and balance — You are stable when the point where your body’s weight is concentrated (the center of mass) stays within the area supported by your feet; when it moves outside that area, you lose your balance. The same principle explains why the forward shift of the center of mass during pregnancy often leads to lower-back stiffness and aching. See Center of mass.
- Lifting objects — Keeping an object close to your body and using the large muscles of your legs as well reduces the load on your lower back. You can find practical tips in Lifting technique.
- Sitting and desk work — Chair height, monitor position, and armrest angles are all design considerations intended to reduce the forces on the neck and lower back. Ergonomics is the field that applies biomechanics to everyday tools and equipment.
A useful perspective to keep in mind
Knowledge of biomechanics is less a formula for deciding “this is the correct posture” and more a lens for understanding your own movements. Even during the same movement, the forces on the body vary depending on height, limb length, joint range of motion, muscle strength, and familiarity with the movement. So rather than treating one posture as the only correct choice, it is better to alternate between different postures and find a range that feels comfortable for your body. You can read more about this perspective in No single ideal posture.
When your body feels uncomfortable, take a moment to consider “which forces are acting where.” If your knee hurts, understanding that going down stairs places a large load on the knee can help you choose options such as holding the handrail or descending slowly. These small applications are examples of using biomechanics in everyday life.