Neuromuscular 3 Flashcards
1
Q
Power Task
A
Short explosive movements
2
Q
Power and movement
- Work
A
- Power relates to how quickly force is applied and movement occurs
- To apply force (F) to an object and move the object a given distance (d) is doing Work.
- Work = F x d
- Power is the rate of doing work with respect to time
- Power = F x d /t
3
Q
Force, velocity and power
A
- Power is strength with speed
- Power = Force (N) x Velocity (m/s)
- Force is inversely related to velocity (continuous line in figure below);
- But the relationship between power and velocity (or force) is more complicated!
- Maximum power occurs at an optimum force and velocity.
- These optima are at about 30 % of maximum force and velocity
4
Q
Factors influencing maximum muscle power
A
- Fmax (previous lecture): increasing strength will increase muscle power.
- Vmax (maximum velocity of shortening) and maximum rate of relaxation (important to repetitive actions).
- Motor unit or muscle fibre type.
- Muscle architecture.
- Neural control and motor unit recruitment.
- Rapid stretch (stretch-shortening cycle).
- Muscle temperature.
5
Q
Muscle shortening and cross-bridge cycling
- Active shortening …
A
- Active shortening of sarcomeres and fibres requires cross-bridge ‘cycling’.
- Cross-bridge cycling depends on ‘ATP turnover’.
- Vmax is highly related to the maximum rate of ATP turnover.
6
Q
Rapid shortening during contraction depends on fast cross-bridge cycling
- The speed of myocyte ….
A
- The speed of myocyte shortening is proportional to the rate of cross-bridge cycling.
- Cross-bridge cycling is an energy (ATP)-powered process and, thus, depends on the activity of the enzyme (myosin ATPase) involved in this process
- The faster the activity of the myosin head the faster the cycling will be
7
Q
Rapid relaxation after contraction depends on rapid reversal of contraction events
A
- Fast pumping of Na+ /K+ pumps to repolarise sarcolemma.
- Fast reuptake of Ca++ by sarcoplasmic reticulum
- Both depend on ATP supply
- More energy goes into relaxing than contraction
8
Q
Relaxation and maximum power during repetitive movement
- To generate high power…
A
- To generate high power, contraction and shortening must be followed by rapid relaxation and lengthening.
- Faster motor units relax more quickly. (fast twitch muscle fibres = larger MUs, Slow twitch muscle fibres = smaller motor units
- (slow MU have a slower decay in force & fast MU relax more quickly)
9
Q
Motor unit type, velocity and power
- tension
A
Types of motor units
- Fast twitch fatigable
- Fast twitch fatigue-resistant
- Slow twitch
The speed to which a fast motor unit gets to its maximum tension occurs much faster than the slow motor unit
10
Q
Neural control influence muscle power
A
- Muscle power is influenced by MU recruitment.
- During a brief explosive movement requiring maximum power, it takes time to maximise MU recruitment and power output.
- This time can be shortened with training.
11
Q
Muscle architecture and shortening velocity
A
- Longer muscles, often fusiform, tend to shorten more quickly.
- Increasing the length of muscle – adding sarcomeres in series – increases the ‘displacement potential’ of muscle.
- This translates into a higher velocity of shortening and power output.
12
Q
Stretch-shortening cycle and power
A
- During many movements muscle lengthens quickly before it contracts.
- Brief, rapid lengthening with some muscle activation prior to a contraction can increase muscle power (e.g., countermovement).
- Mechanisms probably include stretch reflex and utilisation of energy stored in elastic tissue within contracting muscle (e.g., tendons)
13
Q
Temperature affects power and velocity
A
- Rates of ATP hydrolysis (breakdown) and cross-bridge cycling are influenced by temperature.
- Vmax and maximum power output are influenced by muscle temperature.
- The maximum peak power increased as the temperature increased
- The optimum velocity shift to the right as the temperatures increased
- The maximum power that can be generated by contracting muscles in cycling task increases as a function of temperature of muscles.
14
Q
Endurance Tasks
A
- Fire fighters
- Pregnant women
- Older people
15
Q
Endurance
A
- Endurance is “the ability to withstand strain or hardship” (The Collins Australian Pocket Dictionary, 1989).
- During exercise, endurance can be viewed as the maximum time that the exercise task can be sustained for.
- And the exercise task might relate to the intensity (e.g., force, velocity, power) of a particular type of exercise .
- The endurance time coincides with the moment of task ‘failure’, an inability to execute the task properly.
