Basics of Motion and force

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Force is defined as the interaction between two entities or bodies that result in either the acceleration or deceleration of an object. Forces are characterized by magnitude (how much) and direction (which way they are moving). The HMS is designed to manipulate variable forces from a multitude of directions to effectively produce movement. As such, the fitness professional must gain an understanding of some of the more pertinent forces that the HMS must deal with and how they affect motion.

When static balance has been upset, the body has been put into MOTION.  Thus, what is implied is a change of place or position involving direction and speed.  There are three major classifications of motion are

  • Linear motion
  • Curvilinear motion
  • Rotary motion

Linear motion (also known as translation or translatory motion).  Meaning, a person is said to move as a whole with all parts moving in the same direction.  If the path is straight, it is linear.  Linear motion is also referred to as rectilinear motion, although it has become customary to use only the word linear.

Muscular and posture analysis

The universally accepted method of describing human movements is in three dimensions and is based on a system of planes and axes. Three imaginary planes are positioned through the body at right angles so they intersect at the center of mass of the body.

They include the sagittal, frontal, and transverse planes. Movement is said to occur more commonly in a specific plane if it is actually along the plane or parallel to it. Although movements can be one-plane dominant, no motion occurs strictly in one plane of motion. Movement in a plane occurs on an axis running perpendicular to that plane, much like the axle that a car wheel revolves around. This is known as joint motion. Joint motions are termed for their action in each of the three planes of motion.

Plane Motion Axis Example
Sagittal Flexion/extension Coronal Biceps curl, Triceps pushdown, Squat, Front lunge, Calf raise, Walking, Running, Vertical jumping, Climbing stairs
Frontal Adduction/abduction, Lateral flexion, Eversion/inversion Anterior-posterior Side lateral raise, Side lunge, Side shuffle
Transverse Internal rotation, External rotation, Left/right rotation, Horizontal adduction, Horizontal abduction Longitudinal Trunk rotation, Throwing, Golfing, Swinging a bat

There are three types of muscle movements: eccentrically (to decelerate force), isometrically (to stabilize), or concentrically (to accelerate force). Each muscle should be studied at length to examine its functions as well as how it moves synergistically with others. In addition, an isokinetic muscle action occurs at a constant speed, requiring expensive and sophisticated equipment.

Muscles produce a force that is transmitted to bones through their connective tissues (tendons). Because muscles are recruited as groups, many muscles will transmit force onto their respective bones, creating movement at the joints (15–18). This synergistic action of muscles to produce movement around a joint is also known as a force-couple.


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