Impairment of Weakness

Question 1

What causes weakness?

Answer 1

Either, 1) Decreased voluntary drive (i.e. loss of and/or decreased ability to recruit motor units), or 2) Decreased muscle cross sectional area (CSA) or muscle atrophy

Question 2

What is adequate strength?

Answer 2

This is strength that is appropriate for what you need for your work, recreation, and your age. High performance activities need higher strength than regular activities. We can establish adequate strength in neurological conditions (i.e. stroke) by comparing the unaffected or ‘good side’ to the affected side. We can also compared cross-sectional weakness with normative values (again, based on work, recreation and age)

Question 3

What are the measures on the spectrum of weakness?

Answer 3

0: Paralysed - muscles in which there is no palpable muscle contraction
1-2: Very weak - muscles with a flicker of activity, small palpable contraction or limited movement in a gravity eliminated plane
3: Weak - muscles that can move against gravity, but do not have normal strength
4-5: Strong - muscles that are normal/close to normal strength

Question 4

What causes a muscle contraction?

Answer 4

1. A nerve impulse is sent along a motor nerve
2. The release of acetylcholine from nerve endings cross the synaptic cleft
3. Acetylcholine depolarises the muscle cell
4. The action potential travels to the sarcoplasmic reticulum causing the release of calcium
5. All muscle fibres of the motor unit contract (an all or nothing principle)

Question 5

What regulates the strength (i.e. force) of a contraction?

Answer 5

Either, 1) the number and type of motor units, or 2) the initial length of the muscle

Question 6

What is a concentric contraction?

Answer 6

Occur when a muscle contracts while it is shortened

Question 7

What is an eccentric contraction?

Answer 7

Occurs when a muscle lengthens while it is contracting

Question 8

What is an isometric contraction?

Answer 8

Occurs when a muscle stays at one length when generating force

Question 9

Where do we assess muscle strength in contraction?

Answer 9

We need to standardise the length of a muscle in order to get a reliable measure. Measuring the midlength is a sensible decision, but it is also possible to miss end-of-range conditions of weakness by only measuring midlength size. In terms of training, if someone falls into the very weak to weak categories, we may need to start training in the midrange

Question 10

Define muscle force

Answer 10

Force generated by a muscle contraction

Question 11

Define resistive force

Answer 11

Force generated by external force (e.g. weight) and weight of the body part

Question 12

Define lever/moment arm

Answer 12

Perpendicular distance btw the joint centre and the line of force acting on that joint

Question 13

Define torque (moment)

Answer 13

Degree to which a force tends to cause rotation about a fulcrum (joint) – equation for this is FORCE x PERPENDICULAR DISTANCE (the moment arm)