Biomechanics & Movement Science

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Biomechanics & Movement Science
Medical Rehab Terms
Human Performance Terms
Disability Terms/Concepts & Rehab Research Terminology
Prosthetic-Orthotic-Assistive Techn Terms


Contains Tables H-I


H. Basic Movement Actions 

flexion vs extension (hyperextension) 

movement which brings the limbs or body into a more bend vs straighten position (often in sagittal plane)

abduction vs adduction, leg or arm 

moving extremity away from vs toward the body (often in a frontal plane)


circular movement combining flextion, abduction, extension, and adduction

pronation vs supination, forearm 

axially turning the forarm so the palm faces backdown/downward vs forward/upward 

dorsiflexion vs plantar flextion 

bending the ankle so the foot points upward vs downward

eversion vs inversion, foot 

to rotate outward vs inward (e.g., toes), typically a combination of plantar flextion/supination/adduction vs dorsiflextion/pronation/abduction.


I. Biomechanics and Movement Science Terminology

Active Range Of Motion

The range through which a joint can move (typically angular, in one degree of freedom), without assistance or resistance.


To walk.  

Antagonist Muscle

A muscle whose action is the opposite to that of another muscle.

Concentric action

A muscle that shortens while activated.

Constitutive relation

The governing equation describing the relation between two variables (e.g., force -extension relation for a spring). 

Dynamics (Kinetics)

The study of the forces and motion caused by the forces.  Forward dynamics: forces are inputs, motion evolves due to the dynamical equations of motion.  Inverse dynamics: motions are known, forces are then back-calculated.

Eccentric action (plyometric)

A muscle that lengthens while activated


 An activated muscle "contraction" in which its velocity is constant (specified) and the force can change (e.g., depends on the level of effort).


 An activated muscle "contraction" in which its length does not change (special case of isokinetic in which the velocity is zero).


An activated muscle "contraction" in which the force is constant and the length can change (e.g., shorten)

Line of action

The conceptual center line of the pulling force of a muscle

Motor unit

Motoneuron and the muscle fibers it innervates


A muscle crossing more than one joint.

Muscle fiber composition

The relative composition of "slow" and "fast" muscle fibers in a muscle.

Range Of Motion (Rom) 

The normal range of movement of any body joint. Range of motion also refers to exercises designed to maintain this range and prevent contractures.  The "passive" ROM is the range through which a joint can be moved by an external force (e.g., applied by a therapist).

Redundancy (actuator, kinematic)

Actuator redundancy refers to the concept of there being more muscle actuators that necessary to move in the joint degrees of freedom (e.g., more than two muscles cross the elbow joint).  Kinematic redundancy refers to the there being more joint degrees of freedom that end-point degrees of freedom (e.g., arm).

Rigid Body

A body segment that is assumed not to deform; commonly used assumption for movement biomechanics studies (e.g., limb segment).


The local stiffness of a tissue (such as muscle, ligament, bone) or endpoint (such as at hand) is the change in force divided by the change in length.  In reality the "stiffness" can depend on a range of factors, such as the magnitude of the applied change (if nonlinear) or whether it is measured immediately or in steady-state (if history-dependent).  

Synergist muscle

Muscles working together to cause similar actions.

 Yield point

The point of stress on the load deformation curve that separates the elastic range from the plastic range, at which point increased load causes residual deformation after the load is removed.


Copyright by Jack Winters.
For problems or questions regarding this web contact Jack Winters.
Last updated: February 27, 2001.