Muscle Mechanics

Question 1

isometric contractions

• do they have work or power?
• is energy used?
• what are they involved in?

Answer 1

develops tension but stays the same length b/c ends attached to immovable objects

• no external work is performed, so power also equals zero
• ATP hydrolysis is used when muscle exerts tension
• involved in maintaining posture and experiments to investigate muscle properties

Question 2

series elastic elements and contractile elements in isometric twitch

Answer 2

SE (tendon) is springy and lengthens, CE (muscle) shortens, but equally such that the total length remains the same
-reverses during isometric contraction

Question 3

isotonic contractions

• what does the tension curve look like?
• relationship between load, plateau, and time lag between stimuli and start of shortening

Answer 3

force of contraction of muscle is at least equal to load so that muscle shortens (attach muscle to moveable load)

• tension increases as the muscle contracts in preparation to lift (a bit of isometric), but then tension is constant as the muscle shortens and lifts the load (isotonic)
• the greater the load, the higher the plateau, and the greater the time lag between stimuli and start of muscle shortening

Question 4

what kinds of muscle (isotonic/metric) are latissimus dorsi and biceps?

Answer 4

latissimus dorsi: isometric

biceps: isotonic

Question 5

what happens if the load exceeds the amount of force the muscle can generate?

Answer 5

an isometric twitch results, b/c it cannot even lift it to start isotonic

Question 6

4 stages of isotonic twitch

Answer 6

1. isometric tension development (tension develops w/o shortening until force developed equals load)
2. isotonic shortening (shortening of muscle at constant tension)
3. isotonic relaxation (elongation to initial length at constant tension)
4. isometric relaxation (reduction of tension at initial length)

Question 7

curve-wise, what happens for isotonic twitches with heavier loads?

Answer 7

1. longer delay (latency) until shortening occurs
2. initial velocity of shortening decreases
3. distance of shortening decreases and muscle drops weight sooner
   eventually, if it’s too heavy, a point will be reached where muscle cannot lift weight at all (maximal amount of tension for a particular initial length)

Question 8

what is the maximal rate of tension development during isovolumic contraction a measure of?

Answer 8

the strength/health of the heart

Question 9

preload

Answer 9

weight that pulls muscle to a given initial length

Question 10

afterload

Answer 10

equivalent to total tension

Question 11

skeletal contraction cycle for isometric contraction

Answer 11

1. muscle contracts to peak tension

2. muscle relaxes to zero tension