What does isokinetic mean?
constant joint velocity
If there is constant external load, like in lifting free weights, what is the term for that?
Joint torque is a product of what?
muscle force and moment arm
What is muscle force dependent on?
1) muscle structure
2) muscle activation
3) mechanical properties (length/tension, force/velocity)
What are the A and I bands of muscle cell structure?
A = length of only thick filament (stays same) I = length of only thin filament (shortens in contraction)
Name the layers of CT surrounding muscle tissue, most exterior to most interior.
Epimysium -> perimysium -> endomysium -> sarcolemma
What are the myofilaments?
actin and myosin; make up a myofibril, which make up myofiber
Which alignment of sarcomeres is better for force, parallel or in series?
parallel (more CSA)
Are sarcomeres in series better for force or excursion?
What band anchors the thin filament?
How do you find the force for a pinnate muscle?
take the force and multiply it by the cosine of the angle
What does fiber length give you an estimate of?
amount of excursion from the muscle (since fiber length is counting the sarcomeres in series)
What does physiological CSA give you an estimate of?
it’s on an oblique angle, taking into account the pinnation angle, so it gives you an approximate force capacity value
Which has more excursion, soleus or sartorius?
sartorius, b/c it’s longer
What dictates the degree of fiber excursion?
muscle fiber length
What dictates maximal strength of a muscle?
T/F: Muscle length and muscle tension are proportional.
true, after the critical length
What’s the difference between active and passive insufficiency?
- passive = muscle can’t lengthen far enough, since a full stretch at multiple joints can’t occur (filaments too far apart to produce active tension)
• muscle trying to lengthen at 2 joints simultaneously
- active = muscle can’t shorten far enough; excessive overlap of contraction sites
• muscle trying to contract at 2 joints simultaneously
How many degrees of freedom do ellipsoidal joints have? What’s an example of this kind of joint?
- 2 degrees of freedom
- radiocarpal joint
What’s an example of a condyloid joint?
the knuckle, MCP; has 2 degrees of freedom
How many degrees of freedom do plane joints have? What’s an example of a plane joint?
- 3 degrees of freedom
- facet joints, AC joint
What’s the difference between a 2nd class lever and a 3rd class lever?
2nd = resistance at end (better mechanical advantage) 3rd = load at end (better velocity)
What type of joint has irregular joint arranged in a haphazard fashion?
Do ellipsoid joints have flattened concave or convex surfaces?
What’s an example of a condyloid joint?
What is akylosis?
When the joint fuses together; can be due to inflammation or genetics
- ex: akylosing spondylitis = spinal fusion
What’s the difference between arthrodesis and pseudoarthrosis?
arthrodesis = moving joint up surgically pseudoarthrosis = improper healing of a broken bone, resulting in pseudo joint (non-union)
What do synovial plica do?
increase surface area
What type of collagen makes up tendons and ligaments?
What type of collagen is very thick and found in fibrous capsules?
What type of collagen is found in hyaline cartilage and is a little more flexible?
What type of collagen do we transition into more of when we age?
type I: stiffer, not as flexible
What do proteoglycans do?
- imbibe water for disks/menisci via negatively charged sugars
- AAs that branch and bind to core protein
Ligaments and tendons have what kind of dense connective tissue?
What structure contains irregular dense connective tissue?
fibrous joint capsule
T/F: Tissue doesn’t change much after large periods of immobilization.
false; after 6 weeks immobilization, the limbs need a LOT more torque to move them
If a patient is on bedrest for 2 months, how long of physical activity do they need before they regain normalcy?
4 months (double the time of immobilization)
What is on the end of bones to reduce friction and distribute loads?
What is articular cartilage mostly made up of?
1) extracellular matrix (85%): collagen, proteoglycans, water
2) chondrocytes (10%): develop articular cartilage, maintain EM
T/F: If scar tissue builds up, more water is imbibed.
false, less water is taken up
What happens in DJD?
degenerative joint disease = articular cartilage lost, so there’s less lubrication; can have bone on bone
What does articular cartilage do?
lubricate joints for smoother movement; distributes loads so bones don’t get upset
What happens in RA?
RA causes inflammation that breaks down the CT in the body, causing ulnar drift in the hand
What type of cartilage are the labrum, IVDs, and pubic symphysis considered?
fibrocartilage: irregular dense CT
What are the 4 functions of bone?
1) fascilitate body movement, muscle action
2) store minerals
3) provide muscle attachment sites
4) protect internal organs
How long does healthy bone reformation take? What is necessary for this process?
3-4 months; need WB to remodel
What is the most sensitive part of bone that is always remodeling and breaking down?
cancellous, or spongy bone
What types of arteries supply the medullary canal of bones?
What is wolf’s law?
bone remodels according to the stress/load placed upon it
What part of the bone allows it to be strong without being heavy?
trabeculae in cancellous bone (spongy)
At what age are we done building bone? At what age do we decline in bone mass?
- done building at 25
- decline at 70
Describe the bone healing process after a fracture. (We cast to preserve this process.)
1) fracture occurs, blood goes to area
2) fibrocartilaginous callus forms
3) bony callus forms (stronger)
4) bone remodels
T/F: Some bones need more stress than others to stimulate bone reformation.
T/F: Lack of Vit. D and calcium can cause back pain.
true - your bones need it and may be hurting without it
Are load-bearing bones able to get back to BMD baseline after periods of inactivity?
usually still lower than baseline after long inactivity periods (months of bedrest)
Why do we want to encourage patients who are able to, to weight bear after surgery or injury?
- to increase bone remodeling
- to decrease bone mineral density loss from long bouts of inactivity
The velocity of muscle contraction is dependent on what factor?
how heavy the load is that the muscle has to displace
T/F: Lengthening = positive work.
- lengthening = negative work
- shortening = positive work
When considering function, what’s more important: power or strength or velocity?
power (force x velocity)
As length increases, what happens to tension?
T/F: Force decreases with firing frequency.
- false, force increases w/ firing frequency, up to a point
- this is the rate coding: higher firing rates = higher force
What is the order of recruitment for motor unit types?
slow oxidative -> fast oxidative glycolytic -> fast glycolytic
T/F: Fast glycolytic has a high twitch response.
What is rate coding, and what does it do to force?
rate coding = the increasing or decreasing of firing rates of MUs, directly related to the force production
What is the loss of CSA that occurs with old age called?
T/F: The mechanism of transient fatigue is task-specific.
What accounts for a large decrease in muscle strength in the elderly?
T/F: We see increased co-contraction in the elderly.
true, this is a mechanism of weakness for them
What two variables affect EMG values?
the timing of muscle activation and the amplitude
Describe the 3 Newton laws.
1: Law of inertia
2: Law of acceleration
3: Law of action-reaction
How do you use the right hand rule?
align ulnar hand along x, curl fingers towards y
- if thumb goes out of board, “+”
- if thumb goes into board, “-“