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25 Cards in this Set

  • Front
  • Back
After review of the Passive Length-Tension curve in fig 3-5, explain what and
how tension is generated in muscle that is lengthening passively.
A muscle is stretched and once it reaches its critical length tension is generated. Tension is generated because the muscle resisting the stretch.
How do elasticity and viscosity relate to this tension generation?
A steched muscle exhibits elasticity because it can temporarily store part of the energy that created the stretch. Stored energy helps prevent a muscle from being damaged. Viscosity, rate-dependent resistance encountered between the surfaces of adjacent fluid-like tissues. A muscle's internal resistance to elongation increases with the rate of stretch.
After reviewing the Active Length-Tension curve in fig 3-10, explain what
happens to force/tension generation potential in a muscle when that
muscle/muscle fiber/sarcomere is taken out of its ideal resting length? Why?
As the sarcomere is lengthened or shorten from its ideal resting length, the number of potential cross-brige attachments decrease, so the less amount of active force can be generated.
So, describe an active muscle that can produce its greatest force, ie. What is its
length? What does it actin/myosin filament alignment look like?
The ideal resting length of a sarcromere allows for the greatest number of croess-bridge attachments, the greater the amount of active force generated within the sarcomere.
In class demo - Predict grip force production changes as grip spacing varies. (Or
What do you suppose will happen testing grip strength in various amounts of
open grip?)
The more stretched or contracted the less force will be produced. The shorter or longer the muscle, the less grip strength.
Define the terms passive insufficiency and active insufficiency (see your Kendall
text for these terms).
Passive-too long
Active-too short
After reviewing the Total Length-Tension curve in fig 3-11, differentiate when
active vs passive tension components are contributing to the total force
generation of a muscle using muscle length. Explain your answers.
At shortened lengths, all force is generated by actively. As the muscle is stretched beyond its resting length, passive tensioni begins to contribute to the total force. When the muscle is further stretched and passive tension accounts for most of the total force. Both generate forces at resting length.
Using fig 3-12 A & B, discuss what the shape of an internal torque-joint angle
curve indicates about a muscle’s/muscle group’s length or moment arm as
factors in producing force?
Mechanical (Increase or decrease moment arm)
Physiological (Decrease muscle activation or muscle length.) The Longer the moment arm, the more force. Muscle length plays a stronger role than moment arm in producing force
What is the effect on muscle force production from an increased moment arm for
the hip abductors?
The moment arm is the same (given the length stays the same), the length is longest at -10 degrees. Hip abductors are more dependent on length then moment arm.
How do internal torque-joint angle curve shapes relate to functional activities?
(See Special Focus 3-1, p49)
The maximal internal torque potential is greatest in the mid ranges of elbow motion, and least near full extension and full flexion. The hip abductor muscles, the internal torque is greatest near neutral. This joint angle coincides with the approximate angel where the hip abductor muscles aremost needed for frontal plan stability while walking. Large amounts of hip abduction torque are rarely required in a position of maximal hip abduction. Workout to meet optimal conditions.
In reviewing the theoretic Force-Velocity curve in fig 3-15, point to the area of the
graph indicating the amount of force produced during a high speed concentric
muscle contraction?
High speed/low force
Inversely related
In reviewing the theoretic Force-Velocity curve in fig 3-15, point to the area of the
graph indicating the amount of force produced during a high speed eccentric
muscle contraction?
High speed/ High force
Directly related
What do you interpret about muscle accelerator and decelerator functions from a
force-velocity curve?
Eccentric-Deccelator (Slows things down)
Can you predict what is going to happen in the class demonstration of shoulder
flexion in terms force-velocity? (We will have a volunteer move weights into
shoulder flexion concentrically and attempt to control weights against gravity
from a shoulder flexion position.)
The heavier the load the longer it will take.

The lighter the load, the faster.
Which do you think has greater tension capabilites, concentric or eccentric?
Which do you think will have greater EMG activity, concentric or eccentric?
Concentric vs Eccentric
Concentric-active, shortening, contractile
Eccentric-passive, stretching, non-contractile
What is Electromyography (EMG)?
A diagnostic test that assesses the health of the muscles and the nerves controlling the muscles.
Why do PT use EMG?
A tool used by PTs to facilitate or inhibit muscle contraction
How is the EMG performed?
How the test is performed: a needle electrode is inserted through the skin into the muscle or a surface electrode is placed on the skin overlying a muscle. The electrical activity of the muscle detected by this electrode is displayed on an oscilloscope or may be heard through a speaker. After placement of the electrodes, the subject will contract the muscle. The presence, size and shape of the wave form (action potential) produced on the oscilloscope provides information about the ability of the muscle to respond.
Why the test is performed?
EMG is most often used when people have symptoms of weakness and examination (i.e. MMT) shows impaired muscle strength. It can be used to differentiate primary muscle conditions from muscle weakness caused by neurologic disorders
EMGs are also used in kinesiology studies to detect relative muscle activity during functional or sport activities
Muscle Physiology
A muscle cell (fiber), when adequately stimulated by a motor neuron (or an outside stimulus like an electric stim machine), will produce an action potential (bioelectric current) along/through its various membranes
When a muscle is activated via the CNS electrical potentials are generated
These electrical potentials can be picked up by electrodes inserted or placed near activated muscle cells and recorded and amplified using EMG
The magnitude of the EMG signal (visual or auditory) can (better check w/ Dr.Sneed on this) indicate the relative level of muscle force
What is a motor unit?
All the muscle fibers controlled by a single motor neruon.
Needle (indwelling) Electrode
Invasive…needle is inserted through skin and into muscle
Allows greater specificity in terms of muscle region
More reliable for motor unit studies
Allows access to deeper muscles
Requires a high level of technical skill
Surface Electrode
Easy to apply and noninvasive
Detect signals from large area overlying muscle
More reliable for more global studies of muscle function
Does not require a high level of technical skill