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how bones move against one another
center of gravity
the point around which all masses are equally distributed
axis of rotation
a fixed point around which a lever rotates
position and movement in the cardinal planes
A muslce is most flexible when...
when it is the most lax/short
What forces we are concerned with therapeutically?
- Externally applied resistance (splint, cast)
- Friction (hospital socks)
Degree of stability depends on...
Size, Weight, Height, Location
- Size of base of support
- Weight of the body
- Height of COG above BOS (for ex. someone on stilts COG has moved up and is further from BOS)
- Location of COG
The shortest perpendicular distance between an AOR and the action line.
-muscles operate on SHORT moment arms because their insertions are close to the joint axis!
Qualities of a 2nd class lever
Can carry a larger amount of weight for a short distance at a low speed
Qualities of a 3rd class lever
Can carry less weight for a long distance at a fast speed.
using physics to study how forces interact within the body
- non-synovial joint
- Fibrous/Cartilaginous connective tissue
- EX: skull, spinous processses, tibia + fibula, sternocostal joint
- synovial joint
- Articular cartilage
- -joint capsule, synovial membrane, synovial fluid, ligaments, blood vessels, nerves
Periarticular Connective Tissue
- **do not regenerate or have a good blood supply**
- outer layer of joint capsule
- makes up ligaments and tendons
found at the end of the bones that form synovial joints
- tightly woven
- ex: intervertebral disks
- 1 degree of freedom
- Hinge- elbow, PIPs, DIPs (proximal interphalangeal)
- Pivot- skull on the atlas
- 2 degrees of freedom
- Saddle- CMC (carpometacarpal) where you have 'arthritis'
- Condyloid- MCP (metacarpal phalangeal) "no soup for you"
- 3 degrees of freedom
- Ball & Socket- hip, shoulder
2 basic categories of joints, most joints are a version of these:
when Convex moves on Concave...
the joint surface moves in the opposite direction
when Concave moves on Convex...
the joint surface moves in the same direction
Joints can be in 'Action' or in 'Position'. If I were to extend my arm, the action would be extension, but if I paused my arm, the position would be flexion.
Why are joints vulnerable?
- bad blood supply
- -poor recovery potential
- load bearing
- TRAUMA: acute, overuse, inactivity!
- -we need to move to produce synovial fluid, joints depend on motion!
Name the 5 layers within a muscle
- Muscle Fiber
The contractile unit of a muscle/unit of tension is:
What filaments slide past one another int he Sarcomere and how do they interact?
- Actin (thin) & Myosin (think)
- The myosin head attaches to the actin and forms a crossbridge (Oxygen + ATP are required for the motion of the myosin head)
What is a crossbridge
- Necessary for contraction!
- A crossbridge is formed when the myosin head attaches to actin
When a patient has COPD, they are weak, why?
They have low oxygen which is needed for muscle contraction/formation of crossbridges. They are forming fewer crossbridges and are therefore weaker.
What is the ideal resting length of a muscle?
- When the most crossbridges are formed-thus the greatest force with contraction!
- the middle 3rd is where this occurs-most overlap of myosin and actin
A motor unit is made up of:
- neuron, axon, muscle fiber
- Neuromuscular Junction
Motor unit capabilities vary according to:
- Size of cell body
- Type of muscle fiber
- Diameter of axon
- Number of music fibers innervated
Why are the muscle fibers innervated by a single axon not usually located next to one another?
- so that if one axon dies, others can take over it's duties
- smooth muscle movements
The magnitude of a muscle contraction can be altered by:
- --the number of motor units activated
- --frequency of firing
Why are smaller motor units selected first by the nervous system?
- require less energy
- generate less tension
- ALSO, we base it on:
- Previous experience-i know how heavy my book is
- Nature of task-I can SEE that a marble weighs less than a boulder
- Mechanical advantage-of the joint
- Concentric: internal force wins, shortening
- Isometric: no lengthening or shortening
- Eccentric: external force wine, lengthening
- -PICTURE AS ACTIN & MYOSIN
What is an agonist, antagonist, synergist?
- Agonist: prime mover
- Antagonist: opposite direction
- Synergist: assists, stabalizes
What are the characteristics of a Fusiform muscle fiber organization?
- parallel fibers that pull in the same direction
- favor distance!
What are the characteristics of a Pennate muscle fiber organization?
- Fibers run diagonally
- greator force! (less distance)
Compare Fast vs. Slow Twitch fibers
- Fast Twitch
- -fast contraction time
- -fatigue easily (1-5 mins)
- -large motor neuron
- -greater force
- ex: Sprinting
- Slow Twitch
- -slow contraction time
- -resistant to fatigue (hours!)
- -small motor neuron
- -small force generation
- EX: long distance running, posture
MOST MUSCLES ARE A COMBINATION OF SLOW & FAST!
Active tension decreases when...
- the muscle is fully contracted or fully elongated aka sarcomere is too long or short.
- why? It's hard to hold this position for too long,
Passive tension is..
- passive stretch, used in walking (achiles)
- why use passive tension? it does not require energy
Examples of Active & Passive tension in Tenodesis
- Flexion (duck): active are wrist flexors, passive are finger extendors
- Extension: active are wrist extensors, passive are finger flexors
Muscle function is affected by:
- Number + Type of muscle fibers
- Diameter of axon
- Number + Frequency of motor unit firing
What can inactivity and aging do to muscles?
- Inactivity: degradation of proteins, decreased slow-twitch fibers REHAB FOCUS: low intensity, long duration
- Aging: loss of muscle tissue, decreased nerve activation. REHAB FOCUS: balanced, resistive exercise