BASIC MECHANICAL CONCEPTS





Physical therapists are human motion experts. They are particularly sensitive to the internal and external forces that create and modify movement. They understand that influencing factors exerted by the muscular and nervous systems in particular, are crucial to normal movement and how motion is changed when these systems are impaired. Physical therapist assistants must possess equivalent sensitivities as they play their role in rehabilitation.









Force is a vector quantity. Vector quantities have magnitude and direction. Velocity, because it includes direction and magnitude is a vector quality.


Scalar quantities are unidimensional. Scalar quantities only have only have magnitude. Examples of scalar quantities include speed, mass, volume, length.



Newton's Laws of Motion







Kinesiology and Applied Anatomy Application


First Law

Internal and external forces work on the human body and cause or alter motion. Joint motion only occurs if gravity or muscles act upon them. When there is no force there is no motion.


Second Law

Physical therapist assistants are mindful of the orientation of muscle fibers. Oblique, vertical, or horizontal fibers determine the line of pull across the joint and thus the direction of movement. Further the nervous system controls the number of muscle fibers that contract as well as the velocity of the motion.


Third Law

Consider the contraction of lower extremity muscles to facilitate a jumping activity. The muscles must contract to overcome the force of gravity. However, muscles must also contract with the equivalent force upon landing.







Lever Systems and Mechanical Advantage













When muscles actively contract, they may act as the force of movement. When moving a limb against gravity, gravity is the resistor of the movement, and the muscle serves as the force of motion. However, when the limb is moved back to the original position, gravity is now the force of motion. The muscle then relaxes in a controlled manner to resist the force of gravity. This results in shifting from motion in a third-class lever system to a second class lever system with enhanced mechanical advantage.







-CHECKPOINT-



This is a good time to pause and assess your knowledge of key concepts. Below are links to a few learning activities that might assist your mastery of the material.

Completing some of the tasks may also earn you class participation credit! However, most importantly it will assist in your learning.


You should attempt to complete the assignments without using your text, notes, etc., as they are designed to test your knowledge—just like taking a test in class—but without the grade consequences.


Tasks include mock exams, games, clinical scenarios, and more. Click/tap on the activities and see how much you know!


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