Muscle mechanics

Question 1

How is surface EMG used to measure muscle activity?

Answer 1

Gross patterns of action potentials reported by electrodes, the data from which can be processed.

Question 2

How is amplitude related to force produced?

Answer 2

During isometric contraction, is correlative

Question 3

What internal factors affect surface EMG?

Answer 3

Fibre diameter, conductivity, type and location. Number of fibres and active motor units. Unit firing rate. Muscle blood flow, distance between skin surface and fibre, and tissues surrounding muscles

Question 4

What external factors affect surface EMG?

Answer 4

Skin interface, signal conditioning, electrode spacing

Question 5

What is the limitation of surface EMG?

Answer 5

Only gives an indication, rather than an accurate quantitative measure

Question 6

What is a twitch?

Answer 6

A force response of a muscle to a single stimulus

Question 7

What happens if the stimulation is frequent?

Answer 7

Produces a bigger force, and may become a tetanus, creating a tetanic contraction

Question 8

How is muscle activation calculated?

Answer 8

Measure ratio % of tetanus

Question 9

What is active force affected by?

Answer 9

The length-force relationship; maximum force is generated at L0; force is proportional to the number of x-bridges formed, forming a rise-and-fall pattern

Question 10

What is passive force?

Answer 10

Force independent to activation; originates from connectin filament when muscle is over-stretched, developing beyond muscle’s natural length

Question 11

What is the force-velocity relationship?

Answer 11

During muscle shortening, the contractile force is depressed. During muscle lengthening, the contractile force is enhanced.

Question 12

When does muscle become stronger?

Answer 12

When resisting a movement

Question 13

What is the formula for work?

Answer 13

Work = Force*displacement = J

Question 14

What is the formula for power?

Answer 14

Power = F*v = W

Question 15

What happens to velocity when force is increased in concentric contraction?

Answer 15

Is decreased

Question 16

Which type of contraction can develop most force/is most efficient?

Answer 16

Eccentric, as required fewer muscle fibers activated, and fewer motor units, to develop same force output

Question 17

Why does concentric contraction generate lowest output?

Answer 17

Length is decreasing, so x-bridges formed is decreasing, and has to also act against gravity torque

Question 18

When is most power generated?

Answer 18

When muscle is at 1/3 of maximum velocity and 1/3 of maximum force