Basic Biomechanical Concepts fro Human Movement

Biomechanics is the study of tho our joints in our body move and some forces that contribute to those movements. Learning to understand the Biomechanics of the human body is necessary to fully understand our movement.


Torque is an expression of rotational force and all human movement is rotational in nature. Our Limbs act as levers that rotate around fulcra.

Torque is the product of magnitude of force and the {force arm}

The equation for Torque is T=F X FA [Torque equals Force x Force Arm]

When two for es produce rotation in opposite directions, one is the resistance force (R) and its force arm is called the resistance arm (RA). Force generated by R x RA is called Resistance Torque (TR)

Force Arm- is the perpendicular distance from the axis of rotation of the joint to the direction of the force from its point of application (where the muscle attaches to the bone being moved).

Resistance arm-is the distance from the axis of rotation to the center of gravity of the moving limb.

Torque and Exercise-

While exercising, the force arm is the distance from the axis pint (joint axis of rotation) to the point of attachment of the muscle on the bone being moved. The resistance arm is the distance from the axis of rotation to the center of gravity of the moving limb.

Holding a dumbbell lengthens the resistance arm by moving the center of gravity further away from the fulcrum, the longer the resistance arm, the more torque is needed to produce movement.

Torque varies as a limb a limb moves through the joint’s range of motion due to change in the length of the force arm.

Rotational Inertia-

Rotational Inertia the resistance to change in the rotation of a body segment around a joint axis. It depends on the mass of the segment and its distribution around the joint.

For example a lower limb has more rotational inertia than an upper limb not only because it is heaveier but also because its mass is concentrated a greater distance away from its axis of rotation.

Inertia can be manipulated by changing the joint angle (for example) by flexing the knees during running, we move the mass closer to the axis, decreasing inertia.

Angular Momentum-

Angular momentum is the product of angular inertia x angular velocity. The faster a body segment moves, and the greater its rotational inertia, the greater its angular momentum.

The amount of force needed to change angular momentum is proportional to the magnitude of momentum.

Angular Momentum and Exercise-

A faster movement, a greater mass, or a greater desired decelerate requires grater muscle force to slow down the body segment.

Muscles can be injured if they are not strong enough to decelerate the force generated from ballistic movements.

Ballistic Movement-a high-velocity musculoskeletal movement, such as a tennis serve or boxing punch, requiring reciprocal coordination of agonistic and antagonistic muscles



***disclosure: everything in the article I found in the book Fitness Professional’s Handbook Sixth Edition***


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