Generating and Measuring Force and Power Flashcards
1
Q
What are functions of muscle?
A
- Movement
- Contraction/relaxation
- Regulation
- Physical/thermal protection
- Maintains homeostasis
- Blood flow
2
Q
What is concentric contraction?
A
Generating more force than the force against the muscle
(When resistive forces are smaller than the maximal force your muscle can generate)
3
Q
What is eccentric contraction?
A
Doesn’t generate as much force as the force against you
(It can produce more force when being resisted with more force than the muscle can generate to shorten)
4
Q
What is isotonic contraction?
A
The tension/force produced by the muscle remains constant while the muscle length changes
5
Q
What is isokinetic contraction?
A
The velocity of movement remains constant throughout the range of motion
6
Q
What is a motor unit?
A
- The smallest functional unit of force production
- All of its muscle fibres are of the same type
- Its size depends on its movement function
- Units with slow twitch fibres recruited first
7
Q
How can you produce more force?
A
Using more or bigger muscles, activate more motor units in them, at higher frequency (of APs), with moderate muscle length, & optimal angle joint
8
Q
What is skeletal muscle?
A
A highly structured tissue
9
Q
What is the sarcoplasmic reticulum?
A
- Extensive
- Provides support
- Stores, releases & reabsorbs Ca2+
10
Q
What are sarcomeres?
A
Functional unit of fibre, sit end-to-end
11
Q
What is tropomyosin and what does troponin do?
A
- Tropomyosin lies in actin groove & inhibits cross-bridge
- Troponin binds to Ca2+, moving tropomyosin off actin sites for binding to myosin heads
12
Q
What are multiple energy-consuming steps?
A
- Cross-bridge
- Ca2+ re uptake into SR
- Na+/K+ pump on sarcolemma
13
Q
What is required for contraction?
A
- Action potentials arrive at each nerve neuromuscular junction
- Depolarisation of motor end plate (excitation) required to initiate contraction
14
Q
What is excitation-contraction coupling?
A
- Nerve impulse travels down T-tubules and causes release of Ca2+ from sarcoplasmic reticulum
- Ca2+ binds to troponin and causes position change in tropomyosin, exposing active sites on actin
- Permits strong binding state between actin and myosin and contraction occurs
- ATP binding to myosin head weakens its bind to actin
- Each stroke shortens muscle ~1%
15
Q
What is the size principle?
A
Motor neurons recruited progressively by axon size, small to large
15
Q
What are the 2 major benefits of the size principle?
A
- Use fatigue-resistant (type I) units longer
- Finer regulation with low force
16
Q
What happens in motor unit recruitment when frequency increases?
A
- Increase frequency gives big increase in force initially (summation), but diminishing effect with further increased frequency, until tetanus
- To do the same task, it’s about whether its sustainable. You need to recruit more and more motor units which makes the task seem harder and less pleasant
17
Q
Where are muscles activated?
A
- In the CNS
- CNS always receiving feedback from muscles
- “Exercise begins and ends in the brain”
18
Q
What is fatigue?
A
- Reduction in strength
- Can have peripheral and central components
- You will fatigue with no or little ATP depletion and still some glycogen in muscle
19
Q
What is cramp?
A
Generally due to neuromuscular problem, not electrolyte depletion
20
Q
When is force inhibited?
A
Before either ATP or glycogen can become depleted
21
Q
What is the length-tension relationship?
A
- Active tension is a direct function of actin and myosin filament overlap
- Optimal length has most overlap of actin and myosin, so active tension (force production)
- Tension develops rapidly at longer muscle length
22
Q
What is the force-velocity relationship?
A
- Cross bridges between actin and myosin attach/detach at certain rates
- As velocity increases, number of cross bridges decreases and less force generated
23
Q
What is maximal isometric tension?
A
Maximum force it generates just to stay still
24
What is force produced by muscle measured as?
Muscle acts around joints and is measured as torque.
25
Which athletes generate more torque?
Power athletes generate more torque at ALL velocities, compared with endurance athletes, but force drops at similar rates
26
What is the length-tension-velocity relationship?
- If velocity high, force is low, regardless of length
- If velocity low, length is an important force modulator
- At eccentric velocities, muscle velocity dominates length as the determinant of force
27
When is power maximised?
At moderate velocities and moderate force
28
What are the 3 broad ways to classify muscle fibre types?
- Anatomical
- Metabolic
- Physiological/functional
29
What are type I muscle fibres?
- Slow twitch
- Small in size
- High fatigue resistance
- Low force production
- Aerobic
- Duration: hours
30
What are type IIa muscle fibres?
- Moderately fast twitch
- Medium in size
- Fairly high fatigue resistance
- Medium force production
- Long term anaerobic
- Duration: <30mins
31
What are type IIx muscle fibres?
- Fast twitch
- Large in size
- Intermediate fatigue resistance
- High force production
- Short term anaerobic
- Duration: <5min
32
What are type IIb muscle fibres?
- Very fast twitch
- Very large in size
- Low fatigue resistance
- Very high force production
- Short term anaerobic
- Duration: <1min
33
Muscle and strength of children?
- Same muscle quality as adults
- Lack androgenic hormones
34
Muscle and strength of adults?
- Upper body strength: men ~50% > women
- Lower body strength: men ~30% > women
35
Muscle and strength of elderly?
- Strength decreased especially >70years old
- Some loss of Type II fibres
- Decreased precision of force regulation
36
Why loss of muscle and strength with aging?
- Loss of fibre area
- Loss of growth-related hormones
- Decreased IGF-1
- Not just atrophy (=decreased fibre size)
- Also sarcopenia (active loss of muscle mass)
- Accumulate fat and denervated fibres in muscle
- Nerve conduction velocity decreases
37
What is ergometry?
The measurement of mechanical energy production
- Force: resistance to overcome
- Work: volume of exercise
- Power: intensity of exercise
It's fundamental to exercise science and testing at all levels
38
What is an ergometer?
A device from which work and power can be determined. Many types and many modes
39
What are some ergometry applications?
- Measuring fitness, including differences and changes
- Assess which aspects of fitness are well developed or less so.
- Estimate energy used when exercising which depends on: whether its a weight-dependent exercise mode or exercise efficiency
40
What are the main issues in ergometry?
- Make sure you know exactly what you are trying to assess ie. strength, power, endurance, body's response to stress, energy cost of activities
- Are you doing it appropriately ie. is it valid, is it measuring what you want it too, is it reliable
41
Calculation and unit for force?
- Force = mass x acceleration
- Units: N (kg x ms-2)
42
How much Ncm-2 does skeletal muscle generate?
Up to 30Ncm-2 of muscle
43
What is strength?
- The ability to produce force
- Maximum force that can be produced by a muscle group in a single movement
44
What does strength depend on?
- Muscle recruitment
- Muscle size
- FIbre type proportions
- Fibre orientation
- Neural activation
- Metabolic factors
45
What is work?
- The energy imparted into an object when it is moved to a position of higher potential energy
- Work = force x displacement
- Unit: Joule = Nm
46
What does acceleration often relate to in exercise?
- Gravity eg. climbing, jumping, throwing
- Body mass, of you or other eg. sprint, tackle
- Equipment eg. ball, javelin, racquet
47
What is power?
- Rate of doing work
- Power = work/time
- Units: Watts = Js-1
- For most exercise situations, power is the functionally important expression of strength
48
What does power depend on?
- The ability to supply energy fast, on strength, and on resistance not being too high (so that velocity isn't too low)
- Highly trainable
49
What is power often expressed relative to?
- Body mass or lean body mass
- Upper limit attainable
50
What is endurance?
- The ability to maintain force or repeated contractions
- Humans have high endurance capacity
51
What does endurance depend on?
- Energy
- Strength
- Motivation
- Injury
- Thermoreg
- Efficiency
52
How do you measure endurance efficiency?
- Work rate / metabolic rate x 100
- Ranges 0-25%
53
What are air-braked ergometers?
- Concept 2 rowing ergometer, Watt bike and repco cycle ergometers
- Resistance is usually of wind vanes to movement through air
- Resistance and so work rate increases exponentially with cadence (rpm)
54
What are the pros of air-braked ergometer?
Relatively cheap
55
What are the cons of air-braked ergometers?
- Difficult to calibrate (eg. Rely on "physiological calibration")
- Need to know barometric pressure - relies on air pressure (affects resistance)
56
What are friction (mechanically) braked ergometers?
- Eg. Monark Cycle ergometer
- Apply a known mechanical resistance against a flywheel
- As cadence increases, so does work rate; linear relation
- Should take other internal resistances into account
57
What are the pros of friction (mechanically) braked ergometers?
- Easy to use, calibrate and calculate
- Relatively cheap, portable, robust: good for field use
58
What are the cons of friction (mechanically) braked ergometers?
Limited precision of work rate control; reduces reliability
59
What are electromagnetically-braked ergometers?
- eg. velotron & lode cycle ergometers
- Resistance varies inversely with cadence
60
What are the pros of electromagnetically-braked ergometers?
- Wide power range (eg. 0-2000W)
- Fine control of power (eg. change by 1 W every 3s)
- Allows setting of constant power output, or various patterns
- Decrease measurement error by increasing reliability within and between sessions
61
What are the cons of electromagnetically-braked ergometers?
Can be very expensive (>$8000), but some now less so (<$2000)
62
What is treadmill ergometry?
- Usually motorised ie. inclined slope or tethered against a load cell (measures force)
- Work = force x displacement
63
What are some issues with treadmill ergometry?
- Walking on belt can be difficult (clinical more than fitness testing)
- Physiological measures more difficult (BP, bloods, spirometry)
- Increasing slope minimises work of body rise-drop with each stride
64
What are the pros of treadmill ergometry?
- Can be highly specific (eg. runners)
- Encourages central rather than peripheral fatigue
65
What are the cons of treadmill ergometry?
- Cost and size
- Variability in running efficiency. Therefore, less certainty in energy expenditure if it's not measured
66
What is the bench step?
The mechanical work is in raising body. Usually vary work by cadence
67
What is the issue with the bench step?
Need to calculate work, and it ignores negative work (down)
68
What are the 3 types of swim ergometry?
- Tethered swimming
- Swimming power system
- Swim flume (circulating water channel)
69
What is tethered swimming?
- Use load cell or hang weight over pulley
- Limited specificity and little scope for altering power
70
What is swimming power system?
- Swim along pool towing cable attached to generator
- More specific and allows changes in speed to be measured
71
What is swim flume (circulating water channel)
- Specific, versatile and precisely controlled swim ergometer
- Also very good for kinetic and kinematic analyses
72
What are the 6 trends in ergometry: fieldable devices?
- Quantify movement and often couple it with physiology
- GPS, local positioning system and/or accelerometers
- Often linked to physiology
- Valuable info, even if less direct
- Power meters during actual field (and) activity
- Valuable info
