IFS I: Forces, Vectors, and Levers

Flashcards covering the definitions and principles of biomechanics, kinetics, kinematics, vector resolution, and lever systems as described in the lecture.

Biomechanics

The application of the principles of mechanics in the study of biological systems which helps us improve or optimize human movement and performance.

Kinematics

The science of describing movement through qualitative or quantitative analysis.

Kinetics

The study of the relationship between the motion(s) of a body (object) and the forces acting upon them.

Force

A push or a pull upon an object (body) as the result of an interaction with another object.

Vector

A quantity that has both magnitude and direction.

Resultant Force ($R$)

The algebraic sum of vectors acting along the same line or the vector composition of collinear forces.

Percentage Body Weight (Head)

$$8\%$$

Percentage Body Weight (Trunk)

$$50\%$$

Percentage Body Weight (Arm)

$$5\%$$

Percentage Body Weight (Leg)

$$18\%$$

Vector Resolution

The process of resolving component forces into normal and parallel vectors relative to a line of action.

Mechanical Advantage ($MA$)

The factor by which a mechanism multiplies the force put into it, calculated as: $MA = \frac{\text{output force}}{\text{input force}}$.

Lever System Components

A system consisting of a rigid body, a point of rotation (fulcrum), and two forces (effort/force and resistance/weight).

Fulcrum

The axis or point of rotation in a lever system.

First Class Lever

A lever where the fulcrum is located between the load (weight) and the effort (force), such as the triceps acting on the elbow.

Second Class Lever

A lever where the load (weight) is located between the fulcrum and the effort (force), such as ankle plantar flexors acting at the MTP joints.

Third Class Lever

A lever where the effort (force) is located between the fulcrum and the load (weight); these are the most prevalent levers in the body and put muscles at a mechanical disadvantage.

Torque

The strength of the rotational forces acting around an axis, calculated as the force multiplied by the perpendicular distance from the center of rotation ($\text{Torque} = \text{force} \times \text{perpendicular distance}$).

Static Equilibrium

A state where forces are balanced around an axis, such that the sum of the torques equals zero.

Internal Moment Arm ($IMA$)

The perpendicular distance from the axis of rotation to the internal (muscle) force vector.

External Moment Arm ($EMA$)

The perpendicular distance from the axis of rotation to the external (weight/resistance) force vector.

Rotary Component

The component of muscle force that is perpendicular to the bone and produces torque.

Stabilizing Component

The component of muscle force that is parallel to the bone and acts to pull the joint surfaces together.

Forward Head Posture Strain Rule

With every inch that the head projects forward, the load experienced by the muscles to balance the head approximately doubles.