Biomechanics

What are angular forces?

Internal forces. The pull of a muscle on a bone such that it produces movement at the joint. Stabilizing, angular and dislocating can all happen in the same joint

What are stabilizing forces?

Internal forces. The pull of a muscle on a joint brings the ends of joints closer together Stabilizing, angular and dislocating can all happen in the same joint

What are dislocating forces?

Internal forces. The pull of a muscle on bone causes the bones of a joint to move away from each other. Stabilizing/angular/dislocating can all happen in the same joint

gait cycle

Involves a combination of single stance, double stance, open and closed chain movements. There's a lot of torque in our hips. Because of the way the joints of the LE flex and extend during the gait cycle, the COG raises and lowers about 2" during over all cycle

What is Newton's second law?

The acceleration of an object depends on the mass of the object and the amount of force applied. Force = mass x acceleration. The greater the mass, the more force needed to accelerate the mass

What is a first class lever?

The axis is located between the force and the resistance Ex: Triceps causing extension at the elbow (when throwing a ball). Axis = elbow, resistance = arm/ball and force = triceps

Open kinematic chain

- The distal segment is moveable - The proximal segment is fixed - The limb can move in many directions - Ex: knee flexion (kicking a ball). Tibia (concave) on femur (convex) = posterior swing, roll and slide

Describe how a lever changes the amount of force needed for a motion?

- The longer the force arm, the easier it is to move the part - The shorter the force arm, the harder it is to move the part

Active insufficiency

- The point at which a muscle can't be shortened any further - Occurs to agonist - Myosin filaments are contracting the z-lines and the sarcomere can't get any shorter - Muscle has run out of ability to shorten, but still ROM

eccentric contraction

- Joint motion occurs but muscle attachments separate and return to normal resting position - Can produce greater force than concentric - Usually with gravity; muscle contraction used to decelerate movement - Muscle lengthens

concentric contraction

- Joint movement, muscle shortens, and muscle attachments (origin and insertion) move toward each other - Usually against gravity - Acceleration activity

What can make a person more stable (in terms or COG and BOS)?

- Lower COG - A wider BOS - Greater friction

What factors affect client stability?

- Mass of object - Area of object's base - Height of object's COG above BOS - Relationship of LOG to edge of BOS

Explain the function or simple machines

- Used to change the magnitude of force (lever/wheel and axel/inclined plane) - Used to allow force to be applied more efficiently

What osteokinematic motions occur in the transverse plane?

- Medial & lateral rotation - Pronation & supination - Protraction & retraction - Horizontal abduction & adduction - Protrusion & retrusion - Circumduction

isometric contraction

- Muscle attachments don't move - Gravity is not a factor - Neither acceleration or deceleration - Muscle length does not change

What is the function of a pulley?

- Pulley is a grooved wheel w/ a rope or cable riding in the groove, turns on an axle. - Purpose is to change direction of force or increase/decrease magnitude. - Considered a 1st class lever

What is the importance of levers in rehabilitation?

- Saves energy - Makes tasks possible when strength is limited

Transverse plane

- Separate superior and inferior sections - Vertical Axis - Rotational movement

Frontal (coronal plane)

- Separates anterior and posterior sections - Sagittal axis Angular movement

Parallel muscle fibers

- Tend to be longer and thus have a greater potential for shortening and producing more ROM - Strap, Fusiform, Rhomboidal (rectangular) and Triangular

Closed kinematic chain

- The distal segment is fixed - The proximal segment is moveable - Motion is predictable, there's only so many ways that we can move - Ex: Knee flexion (squatting). Femur (convex) on tibia (concave) = posterior swing & roll, anterior slide

Pennate muscle fibers

- AKA oblique muscle fibers tend to be shorter but are more numerous per given area, which means they tend to have greater strength potential but smaller ROM potential

What osteokinematic motions occur in the frontal plane?

- Abduction & adduction - Inversion & eversion - Lateral flexion - Scapula depression & elevation

What is torque?

- Ability of force to produce rotation around an axis - The amount of force needed by a muscle contraction to move in rotary joint movement - Torque = distance x force

Length-tension relationship

- Amount of tension produced by a muscle is a feature of its length - Amount of force a muscle can generate affected by length-tension relationship - Optimal sarcomere length between 80-120%

What are the different parts of a lever?

- Axis or fulcrum (joint) - Resistance or load - Force or effort (muscle)

What is muscle insufficiency?

- Conditions under which a multi-joint muscle cannot be shortened or lengthened far enough to allow all the joints the muscle crosses to move through their full ROM. - Only occurs at two joint muscles

What does a vector quantity describe?

- Describe both magnitude and direction - Size of force is the sum of all forces action on object - If force acts in same direction, magnitude increase - If forces act in different directions, magnitude decrease

Examples of pulleys in the body

- Fibularis longus and the lateral malleolus - Quadriceps and patella

What osteokinematic motions occur in the sagittal plane?

- Flexion & extension - Dorsiflexion & plantar flexion (ankle

What is force?

- Force gives us power - Created when one object acts on another. Can either push or pull - Force = mass x acceleration

Define moment arm

- How much torque is needed depends on force + length of the moment arm, which is the perpendicular distance between the center of joint (axis) and muscle's line of pull - MA length is greatest when angle is 90 degrees; decreases force needed - MA length shortens as joint angle increase/decrease; increases force needed

Passive insufficiency

- When a multi-joint muscle can't be lengthened any longer - Occurs to antagonist - Trying to lengthen a muscle over two joints impacts POM. - Can't flex hips to touch toes and extend knees because that would be lengthening hamstring along both joints. Generally need to flex to touch toes

How does COG change?

- When mass is added, COG moves towards mass - When mass is subtracted, COG away from lost mass - Makes it's biggest change typically either anteriorly or posteriorly

What is the function of a wheel and axle?

- it is a large wheel connected to a smaller wheel and typically is used to increase the force exerted. - Turning a larger wheel or handle around an axle requires less force, where as turning just axle requires more force. - Occurs at ball and socket joints

Sagittal Plane

- separates right and left portions - Frontal axis - Angular movement

Why is biomechanics, kinesiology and anatomy important for OT?

1. Common language with other medical professionals 2. Safety for me and patient 3. understand principles that govern muscle movement Movement analysis Adaptive equipment

What's the importance of the LOG and it's relationship to BOS?

A client is most stable when their LOG is w/in the confines of the BOS. If the LOG shifts outside the BOS, that person is unstable and more likely to fall

Agonist

AKA "prime mover", directly performs specific movements, contraction

What is a reactive force?

External force that arises in response to active force and disappears the instant active force is gone. Ex: Person pushes off arm rests on a wheel chair and the chair moves backwards

Why is it important to place an object at intermediate heights during a lift?

Allows for re-positioning trunk and BOS; gives body a rest

Irritability

Ability to respond to a stimulus. A muscle contracts when stimulated

What is Newton's first law?

An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

What is angular (rotary) motion?

Body part moves along a plane of motion and around an axis of motion

What is curvilinear motion?

Body part moves along a plane of motion but not around an axis of motion. Ex: Scapular elevation or depression

What is rotational motion?

Body part moves around an axis of motion but does not appear to move along a plane of motion Ex: touching your belly by rotating the humerus in the transverse plane around a longitudinal axis

Double stance (standing)

Both feet are down and the weight is equally distributed between them. The two potential axis of motion, the right and left hips, have equal force going through them. There's no torque on the system.

What is resistive force?

External force. Another active force that opposes the force of something trying to move. Ex: a boat moving through water experiences water resistance.

What is kinetic friction?

External force. Drag between two surface when moving. Ex: Chair actively being pushed on ground

What is static friction?

External force. Drag between two surfaces but not moving. Ex: A chair on the ground

What is center of gravity?

COG is the point where all the planes meet in the human body. Point where body's total mass is concentrated

Neutral equilibrium

COG stays the same as an object moves. Ex: ball rolling on horizontal surface or person rolling in a wheel chair

What is shear force?

External force. Two forces moving in opposite directions. Ex: Moving patient on a bed by shifting them along surface or rubbing hands together

How does a muscle shorten?

Contracts concentrically so that origin and insertion move closer together

How does a muscle lengthen?

Contracts eccentrically so that origin and insertion move farther apart

Why is it important to keep back vertical during lifts, while carrying?

Decreases the gravitational torque on the back and neck. Torque at hips is greater, therefore force on back increases

Why is it important to never lift or carry with a twisted/rotated back?

Decreases torsion on vertebrae, keeps them straight, carrying position. If you keep everything stacked up, decreases shear and torsion forces (internal forces)

What is osteokinematics?

Describes the movement of bones during an action

What is arthrokinematics?

Describes the movement of the joint surfaces during an action

Explain the concept of equilibrium

Equilibrium is when an object is balanced and all forces acting on it are even. No unbalanced forces or torques acting on an object. Object either motionless or in a state of constant velocity

What is pressure force?

External force applied over a given area (of tissue). Ex: pressure sores

What is Newton's third law?

For every action there is an equal and opposite reaction

What are the components of a force?

Force is a vector quantity because it has 4 components 1. Magnitude 2. Direction 3. Point of application 4. Nature (either compressive or tensile)

Fixator

Function is to stabilize joint during motion

Unstable equilibrium

If COG/LOG is slightly off or BOS is more narrow. Requires much less force to disturb stability

What is a biaxial joint?

Move around 2 axes, in 2 planes. Condyloid and saddle

Close-packed position

Joint congruent and surfaces have max contact with each other. Joint tightly compressed, difficult to distract. Ligaments and capsule holding it together taut. Usually occurs in one extreme ROM. Point of greatest stress of joint. Ex: extension of wrist/hip/knee

Open-packed position

Joint incongruent and surfaces have less contact with each other. Joint more easily distracted (passive separation). Ligaments and capsule holding joint together looser. AKA resting position. Joint can roll, spin and slide.

What is a multiaxial joint?

Moves around 3 axes, in 3 planes. Plane and ball and socket

What is a uniaxial joint?

Moves around one axis, in one plane. Hinge and pivot

Why is it important to flex at hips and knees, not back, to reach for a lift?

Lowers the COG toward the floor and keeps the back vertical. Decreases over all torque. LOG stayed over BOS. When mass moves forward, so does COG. When LOG starts to go over the edge, you have to use more force because there's more torque

Why is it important to keep feet shoulder width apart, staggered anteriorly/posteriorly when lifting over the shoulder?

Maintain an increased BOS in the direction of the anticipated force

What is translatory motion?

Motion in a straight line, all points of a body part move at the same velocity

Antagonist

Muscle located opposite of the agonist

Synergist

Muscles that assist agonist in an action

Static equilibrium

Object is motionless. All forces and torque = zero. Nothing is affecting BOS, COG or LOG

What are parallel forces?

Occur in the same plane. They may be in the same direction or opposing each other. Can be perpendicular forces, as long as it's on the same plane.

Examples of wheel and axle

Occurs at ball and socket joints. Wheel = forearm and hand Axle = humerus

Spinning joint

One joint surface rotates on a fixed joint surface. A single point contacts a single point. ALWAYS occurs about a central longitudinal axis of rotation. Ex: Rotation toy top spinning on one spot on the floor

Sliding/gliding joint

One surface glides along the other. A single point contacts multiple other points. Ex: stationary tires skidding across an icy patch of pavement

Why is it important to use smooth motions with lifting?

Prevents strain on small vertebral muscles

Convex-Concave Rule

Roll and slide occurs in OPPOSITE direction. Ex: Femur (convex) articulates with tibia (concave). Roll and slide occur in opposite directions because we want to maintain joint congruency

concave-convex rule

Roll and slide occurs in the SAME direction. Ex: Tibiofemoral joint flexion in open kinematic chain. Roll = posterior, slide = posterior

rolling joint movement

Round end of long bone rolls along the curved side of another. Multiple points contact multiple points. It is a rotary movement. Ex: Tire rolling along pavement

Why is it important to delay lifting by sliding objects as long as you can?

Reduces the amount of time maximal torque must be produced

Why is it important to lift and carry loads as close to the body as possible?

Shorter gravitational moment arm reduces gravitation torque. Decreases torque and keeps mass consolidated over BOS

Summarization of muscle properties

Stretch a muscle, and it will lengthen (extensibility). Remove the stretch, and it will return to it's normal resting position (elasticity). Stimulate a muscle and it will respond (irritability) by generating force (contractility); then remove the stimulus and it will return to its normal resting position.

What is a third class lever?

The force/effort is in the middle. Most common lever in the body, prioritized speed over strength. Advantage: speed and ROM. Ex: Bicep causing flexion at the elbow. Axis = elbow joint, force/effort = biceps and load/resistance = arm/weight

What is a second class lever?

The load/resistance is in the middle. Advantage: power. Ex: Gastrocnemius causing plantar flexion at the ankle. Axis = ankle/toe joints, load/resistance = weight or the body and force/effort = gastrocnemius

Contractility

The muscles ability to contract and generate force when it receives adequate stimulation. This may result in the muscle shortening, staying the same or lengthening.

Elasticity

The muscles ability to recoil or return to a normal resting length when the stretching or shortening force is removed

Extensibility

The muscles ability to stretch or lengthen when a force is applied

Why is it important to try and use your elbow on your knee as a crane when possible?

Transmits weight of object through the leg and not through the back. Decreases some torque

What are concurrent forces?

Two or more forces act on a common point, but push/pull from different directions. Overall effect called a resultant force

Why is it important to lift with the legs, not with the back?

Use the stronger, larger hip muscles to decrease torque

Dynamic equilibrium

When a body or object is moving with no change in speed or direction

Double stance (walking)

When walking, even when in a position of double stance, torque on both of the hips isn't going to be the same because the moment arms will be different due to the varying position of the limbs.

Single stance

With one leg not supporting any of its own weight, the system becomes unbalanced. The side in the air generate torque on the hip of the side in single stance. The hip abductors on the leg in stance need to generate an amount of torque on the hip equal to the amount of torque on the hip being generated by gravity pulling on the leg in the air, otherwise you'll see the hip of the leg in stance move in the frontal plane until the ligaments of the joint capsule create enough force to counteract the torque