Muscle structure & training principles Flashcards
muscle structure
contractile proteins
- myosin: thick filaments with globular heads
- actin: thin filaments
(actin, tropomyosin, troponin)
mechanisms of muscle contraction
- 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
sliding filament theory
- ATP is hydrolysed when myosin head is unattached
- troponin-Ca2+ complex pulls tropomyosin away, exposing myosin binding sites - ADP + Pi are bound to myosin as myosin head attaches to actin
- ADP + Pi release causes head to change position and acting filament to move
- binding of ATP causes myosin head to return to resting position
role of Ca2+ in muscle contraction
- 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
role of ATP in muscle contraction
- 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
excitation-contraction coupling
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
muscle fibre types
- 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
Type I
- 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
Type II
- 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
Type IIa
- 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
Type IIx(b)
- 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
distribution of fibre types
- 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
determinants of fibre type
- Genetics ~50%
- Environment ~50%: Training, physical inactivity
- Significant differences between individuals
assessment of fibre types (muscle biopsy)
- 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
purpose of training
- 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
principle of training (3)
- Specificity
- Overload
- Reversibility
specificity
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
overload
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
adaptation
- 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
overload and fatigue
A properly designed program will allow for adequate recovery while imposing sufficient stress
reversibility
- Training adaptation is not permanent
- Training adaptations will decay once the stimulus has been removed
monitoring training loads
- 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)
training intensity
- 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
determining training intensity
- 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
Karvonen’s HR reverse method (training intensity)
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
