Muscle structure & training principles

Question 1

muscle structure

Answer 1

contractile proteins
- myosin: thick filaments with globular heads
- actin: thin filaments
(actin, tropomyosin, troponin)

Question 2

mechanisms of muscle contraction

Answer 2

• Myosin head binds to an active site on actin (‘cross bridge’)
• Myosin head moves pulling actin filaments towards the centre of the sarcomere (‘power stroke’)
• Sacromere shortens, muscle shortens, force is generated
• Cross bridges detach
• Dependent upon sufficient Ca2+ and ATP

Question 3

sliding filament theory

Answer 3

1. ATP is hydrolysed when myosin head is unattached
   - troponin-Ca2+ complex pulls tropomyosin away, exposing myosin binding sites
2. ADP + Pi are bound to myosin as myosin head attaches to actin
3. ADP + Pi release causes head to change position and acting filament to move
4. binding of ATP causes myosin head to return to resting position

Question 4

role of Ca2+ in muscle contraction

Answer 4

• At rest, myosin and actin are unable to bind d/t tropomyosin and troponin
  o Tropomyosin covers the binding sites on actin
  o Troponin holds tropomyosin in place
• Ca2+ binds to troponin moves tropomyosin away to expose myosin binding site on actin

Question 5

role of ATP in muscle contraction

Answer 5

• Myosin head contains a binding site for ATP
• ATP –> ADP + P = cross bridge + power stroke
• A new ATP binds to myosin to release it from actin

Question 6

excitation-contraction coupling

Answer 6

Sequence of events that begin with a neural impulse and end with contraction

• Excitation of a motor nerve
• Propagation of an action potential
• Events at the neuromuscular junction
• Calcium release from sarcoplasmic reticulum
• Sliding Filament Theory
• Muscle contraction

Question 7

muscle fibre types

Answer 7

• Type I fibres (slow twich)
  -Type II fibres (fast twitch)
  o Type IIa
  o Type IIx (IIb)
• Differences in speed of contraction, maximum force production, oxidative capacity, fatigability…
• Power production is the key determinant of recruitment

Question 8

Type I

Answer 8

• Relatively small in diameter
• Slow contractile speed
• Low force production

- High oxidative (aerobic) capacity
o Many mitochondria
o Many capillaries
o Lots of myoglobin
o Great aerobic enzyme activity

• Highly resistant to fatigue
• Dominant muscle fibre during exercise below CP

Question 9

Type II

Answer 9

• Relatively large in diameter
• Fast contractile speed
• High force production
• High glycolytic capacity
  o Lots of glycolytic enzymes
  o Greater glycogen and PCr stores
• Highly fatigable
• Recruited during high-intensity exercise

Question 10

Type IIa

Answer 10

• Moderately well-developed oxidative capacity
  o Many mitochondria
  o Moderate number of capillaries
• Gradually recruited during exercise bouts >CP
  o i.e. High intensity aerobic exercise <40min – 1hr. Typical anaerobic exercise bouts

Question 11

Type IIx(b)

Answer 11

- Largely anaerobic
o High contractile speed, force, power
o Great glycolytic capacity
o High concentration of CP
o Slight oxidative capacity
o Highly fatigable

• Recruited during short (<1min), very high-intensity anaerobic exercise, when requirement for force and/or speed is high

Question 12

distribution of fibre types

Answer 12

• Skeletal muscle contain both type I and type II fibres however the proportion of these fibres differ
• Postural muscles – higher proportion of type I
• Power muscles – higher proportion of type II
• e.g. Gastrocnemius vs. Soleus

Question 13

determinants of fibre type

Answer 13

• Genetics ~50%
• Environment ~50%: Training, physical inactivity
• Significant differences between individuals

Question 14

assessment of fibre types (muscle biopsy)

Answer 14

• Site is anaesthetised
• Small incision is made (1-3cm)
• Needle is inserted into the muscle
• 10-100mg sample is extracted (~grain of rice)
  o Not too big to reduce impact on performance
• Samples from metabolically active sites
  o e.g. deltoids in swimmers
• Sample is stained to identify fibre type

Question 15

purpose of training

Answer 15

- Improvements in health and performance
o Cardiorespiratory fitness
o Muscular strength and endurance
o Body composition
o Flexibility
o Speed
o Agility 
o Power
- Adaptation: Key to training

Question 16

principle of training (3)

Answer 16

• Specificity
• Overload
• Reversibility

Question 17

specificity

Answer 17

Responses to training are specific to the type of exercise, the muscle groups involved and the energy systems used

SAID principles
- Specific Adaptation to Imposed Demands
o Adaptations are specific to the stimulus
o No adaptation = no improvement
o Lack of specificity results in a reduced training stimulus

Question 18

overload

Answer 18

Training load must be at a level beyond which the athlete is accustomed for improvements in performance

• For continued improvements to occur the athlete must be progressively overloaded
  o As fitness increases the body becomes more resilient to stress, recovery is faster, and initial training loads are highly achievable
  o To ensure continued improvement, the stimulus must increase (or vary)
• Progressive overload is the key to achieving improvements without overtraining

Question 19

adaptation

Answer 19

• Improvement is only possible if this sequence is followed:
• Increasing stimulus (load) –> adaptation –> performance improvement
• If the load is always the same adaptation occurs in the initial stages followed by a plateau
• Same stimulus –> plateau –> lack of improvement
• If the stimulus is excessive or overly varied the athlete will be unable to adapt (maladaption)
• Excessive stimulus–> maladaption –> decrease in performance

Question 20

overload and fatigue

Answer 20

A properly designed program will allow for adequate recovery while imposing sufficient stress

Question 21

reversibility

Answer 21

• Training adaptation is not permanent

- Training adaptations will decay once the stimulus has been removed

Question 22

monitoring training loads

Answer 22

• The FITT principle
• Training loads can be monitored (and modified) by assessing:
  o Frequency – how often
  o Intensity – how hard
  o Time – how long
  o Type – training method(s)

Question 23

training intensity

Answer 23

• Energy expenditure or work per unit time
  o The effort invested into a training session
• Often regarded as the most significant component of the training stimulus for applying overload
• Important to monitor

Question 24

determining training intensity

Answer 24

- Methods
o % of VO2max
o % of CP or LT etc
o RPE
o HR (Most common and accessible, Monitoring HR is an indirect estimate of O2 consumption in exercise, Used to indicate the overload placed on the body)

• The maximal heart rate method
• Training heart rate (THR) is calculated from maximal HR only
  o Maximum HR ~220 – age
  o THR = % of maximum HR
• For trained athletes, THR for endurance training should be between 85-95% HR max
• Lower for recreational athletes

Question 25

Karvonen’s HR reverse method (training intensity)

Answer 25

HRR = difference between resting and maximal HR
o HRR = HR max – HR rest
o Training HR (THR) can be determined as a % or HRR plus resting HR (Should be at least 60% HRR + HR rest)

• e.g. HR max = 200 bpm HR rest = 60 bpm
• HRR = 200-60= 140 bpm
• 60% of 140 = 84
• THR = 84+ HR rest (60) = 144bpm
  o For trained athletes: 80-85% HRR + HR rest