Muscle Contraction and Properties

Question 1

Isometric

Answer 1

• Joints held in fixed position
• Maintains posture and stabilises joint complexes

Question 2

Concentric

Answer 2

• Muscle shortens during activation to do work and output power

Question 3

Eccentric

Answer 3

• Muscle lengthens during activation due to external force being greater than activation force
• Work done on muscle and energy absorbed

Question 4

• Eccentric immediately followed by concentric power generating phase
• Eccentric phase preserves high force via elastic energy which contributes to concentric power generating phase

Answer 4

Maughan and Gleeson (2004)
(Stretch-Shortening Cycle)

Question 5

• Force generation depends on sarcomere length
• Short = opposite ends of sarcomeres overlap and force is reduced (reduced active tension)
• Optimal = max number of cross bridges so greatest active force
• Long = reduced actin-myosin overlap, less cross bridges formed (increased passive tension)

Answer 5

Sergeant (1999)
(L-T Relationship)

Question 6

• Shortening velocity increase = force generation decrease (hyperbolic)
• Max force at 0 velocity (isometric), but goes higher in lengthening then plateaus

Answer 6

Sargeant (1999)
(F-V relationship)

Question 7

• Max power (optimum velocity) is generated at 30% max shortening velocity
• Power drops outside of this due to force or velocity becoming limiting

Answer 7

Sargeant (1999)
(P-V relationship)

Question 8

Determinants of Max Strength and Power
(Activation)

Answer 8

• Max activation needed for max force
• MVC can be tested via electrical stimulation to muscle or nerve

Question 9

Determinants of Max Strength and Power
(Sarcomere in series or parallel)

Answer 9

Series:
- Contribute to fascicle length and contraction distance/velocity
- Force output = one sarcomere

Parallel:
- Contribute to CSA and force production
- Shortening distance = one sarcomere

Muscle power needs to be normalised to volume to take both into account

Question 10

Determinants of Max Strength and Power
(Fibre type)

Answer 10

Type I:
- More force and power at lower velocities
- Lower optimum and max shortening velocities

Type II is vice versa

Question 11

Determinants of Max Strength and Power
(Plasticity)

Answer 11

• Fatigue can transform fibres towards slower characteristics (Vmax and power is reduced)
• Increase in temperature can increase velocity and power