Week 3: Physiology of Strength & Power Training Flashcards
In dynamic concentric exercises:
Muscle length….
Function….
Context…
Decreases
Acceleration
Muscle active, contractile force greater than resistive force
In dynamic eccentric exercises:
Muscle length….
Function….
Context…
Increases
Deceleration
Muscle active, contractile force less than resistive force
In static isometric exercises:
Muscle length….
Function….
Context…
No change
Stabilisation
Muscle active, contractile force equal to resistive force
Resistance types…
What is an isotonic load?
What is a isokinetic load?
What is plyometric?
What is speed?
What is PNF
Isotonic load: constant resistance load but contractile force required varies by joint angle and muscle length eg dumbbell curl or bench press (differences in joint angle change the amount of force required). Variable resistance load to maintain contractile force required throughout range of motion. Eccentric load focusing on contraction during muscle-lengthening phase of exercise.
Isokinetic load: Mechanically braked loading at fixed speed to target/measure specific joint velocities
Plyometric: Focus on force development after sudden eccentric loading using elastic properties of muscles/tendons
Speed: Focus on overcoming resistance as quickly as possible
Proprioceptive neuromuscular facilitation (PNF): Focus on muscular inhibition/relaxation through isometric/concentric loading followed by passive stretching.
What is power?
Power = Work/Time
= Force x Distance/Time
= Force x velocity
What is rate of force development? How is it calculated?
An index of explosive strength
Calculated as the change in force per change in time ie RFD = change in force/change in time.
On a force/time curve, the steepest part indicates…
Peak RFD
The steeper the curve, the more explosive the athlete/action.
True or False - In sport, rate of force development is often more desirable than maximal force production
True
Force-velocity relationship
Less time for actin-myosin cross bridge cycles results in …. contractile force
Greater forces are produced in …. and …. muscle actions
Power can be targeted or RFD close to where the ….. occurs at the intersection with ……
Lower contractile force
Eccentric & isometric
Optimal velocity, maximal power output
Neural activation
- Muscle contractile strength depends on the …., …. and …. of neural activation
- When a motor unit fires, …. the muscle fibres it innervates are activated
- Neural component measured using ….. (iEMG)
- Greater electrical activity indicates …. motor unit recruitment or ….. motor unit firing rate
- Muscle contractile strength depends on the frequency, magnitude and duration of neural activation
- When a motor unit fires, all the muscle fibres it innervates are activated
- Neural component measured using electromyograph (iEMG)
- Greater electrical activity indicates greater motor unit recruitment or increased motor unit firing rate
Motor unit coordination
*Improved MU …. : ability to activate …. number and …. motor units
* Improved MU …..: ability to activate …. motor units … and with minimal latency
* Improved MU … ….: increased …. rate of motor units (discharge rate)
All contribute to increased ….. and …..
- recruitment, greater, size
- synchronisation, multiple, simultaneously
- rate coding, firing
- maximal force production, rate of force development
Integrated EMG analysis show that eccentric loading results in around ….. greater neural activity
7x - develop more force using eccentric training but there are trade-offs with muscle damage and soreness which need to be considered.
Neural disinhibition (preventing the inhibition of muscle contraction)
With long term training we have improvements in our proprioceptive responses to muscle tension. These include:
Muscle spindles: improved sensitivity to muscle fibre stretch deformation, signalling for activation of motor neuron – results in better control of the degree of muscle activation required to overcome resistance.
Golgi tendon organs: Improved ability of motor cortex to override GTO reflexive inhibition of muscle tension – allows muscle to produce greater contractile force
These contribute to increased force production and greater control of contractile force.
Intermuscular coordination components?
These contribute to…..
Synergist coactivation -
Antagonist co-contraction
Cross education
These contribute to improved contraction effectiveness, joint stability, bilateral muscular strength balance and overall force production
What is synergist co-activation
improved ability to activate synergist muscles that contribute to joint stability – particularly relevant in ballistic contractions (eg plyometrics, sprinting)
What is antagonist co-contraction?
ability to coordinate or reduce activation of antagonist muscles resulting in increased force production with same MU recruitment, improved movement control
What is cross education?
Performing unilateral exercise results in increased strength in contralateral muscle, suggesting a central neural adaptation account for a lot of strength improvement.
Significance of adaptations to strength/power training
Increased IEMG activity
Increased maximal force production, RFD
Significance of adaptations to strength/power training
Increased rate of MU activation
Increased RFD
Significance of adaptations to strength/power training
Increased MU synchronisation
Increased RFD and ability to activate high
Significance of adaptations to strength/power training
Increased duration high threshold MU activation
Significance of adaptations to strength/power training
Increased stretch reflex sensitivity facilitating contraction
Increased RFD by assisting elastic components
Significance of adaptations to strength/power training
Decreased activity of golgi tendon organs
Decreased inhibition of maximal muscle contraction
Significance of adaptations to strength/power training
Increased coordination of antagonist muscle groups
Increased maximal force production and contraction effectiveness
Significance of adaptations to strength/power training
Increased contralateral cross training
Increased strength balance between left and right side of body
- The majority of early strength gains during a training program are the result of …. adaptations
- Eventually, myogenic factors begin to contribute to strength development with ….. becoming evident from ~….
- Continued overload can lead to further improvements in strength from neural and muscular adaptations, however total hypertrophy achievable is limited by …..
Neural
Muscle protein accretion, ~6 wks onwards
Genetic factors (myosin)
What is myoplasticity? Is remodelling specific to imposed muscle stimuli? What happens to muscle with reduced use?
Muscle is a highly responsive and adaptive tissue
Remodelling is specific to imposed muscle stimuli
It down regulates
What is hypertrophy? Transient vs chronic
Transient: pumping up of muscle during single exercise bout due to fluid accumulation from blood plasma in interstitial space of muscle
Chronic: increase in muscle size after long-term resistance training due to changes in fibre size
Fibre type changes
- Hypertrophy greater in ….. MHC IIa fibres
- IIa fibres determine maximal force capacity
- Fibre type hypertrophy determined by training intensity – different metabolic stress results in …..
- Resistance training causes acute release of …. …. …. ….
Fast twitch
Fibre type specific hypertrophy
MHC IIx mRNA isoforms
Metabolic signals
- ….. …… mediates the exercise-induced skeletal muscle response to resistance (and endurance) training
- Resistance training induces increased activity in the …… signalling cascade
This modules …… …… ….., leading to muscle hypertrophy - ….., ….. …. play important roles in promoting muscle growth
- Important to note that increased ….. during endurance training signals …. which inhibits/promotes …. activation. This results in …. muscle protein synthesis
Intracellular signalling
PI3-k-Akt-mTOR, muscle protein synthesis rate
Testosterone, IGF-1 and GH
AMPK, TSC 1/2, inhibits MTOR, reduced
Protein synthesis
Feeding and resistance training can modulate MPS and MPB balance
- MPS>MPB = anabolic state
- MPB>MPS = catabolic state
Chronic positive net protein balance results in hypertrophy
anabolic state
catabolic state
Chronic positive net protein balance results in hypertrophy
Contractile components
- The ….. properties of muscle tissue allow it to be ….; absorbing force and enhancing force development
- Divided into …. (SEC) and …. elastic components (PEC)
- Relevant in stretch shortening cycle (SSC) where …. energy is stored in …., ….. (PE) converted to ….. energy (KE) and elastic recoil aids force development
- Elastic components are …., particularly with …. and … exercise
- SSC ….. with fatigue
Viscoelastic, stretched
Series, parallel
Elastic, SEC,
Potential energy, kinetic energy
Trainable - power & plyometric
Decreased
Other structural adaptations to resistance training and their significance
Increased muscle fibre size (CSA)
Increased muscle contractile capacity
Other structural adaptations to resistance training and their significance
Increased Myosin heavy chain (MHC) IIa isoforms
Decreased myosin cycling rate
Other structural adaptations to resistance training and their significance
Increased pennation angle
Increased force production capabilities
Other structural adaptations to resistance training and their significance
Increased type I and II fibre area
Increased strength, reflecting selective recruitment
Metabolic adaptations to strength & power training
Enzyme activity
Metabolism
Substrate storage
Cardiovascular
Metabolic adaptations & their significance
increased fat free mass (increased resting metabolic rate)
Increased PCr, PFK, myokinase content (increased anaerobic work capacity)
Increased ATPase activity (Increased dephosphorlyation rate of ATP for energy)
Increased insulin sensitvity (increased blood glucose control)
Increased intramuscular glycogen storage (increased availability for glycolysis, energy)
Decreased capillary density (increased diffusion distance, anaerobic demand)
Decreased mitochondrial density (decreased relative oxidative metabolic capacity)
Muscle damage and soreness (metabolic)
- Acute soreness:
- ….. accumulation
- Tissue ….. (swelling)
- Delayed onset muscle soreness (DOMS)
- Structural ….. to ….. (tendons, fascia) and ….
- Nerve endings stimulated by potassium/histamine
- Muscle spasm due to decreased …..
- Onset within …. hours of exercise and can last …. days
H+, oedema
Microdamage, connective tissue, cell membrane
02
24hrs, several
Potential mechanism for DOMS
Damage to the muscle due to high tension, particularly during eccentric, intense or prolonged exercise
Injury tends to tissue oedema and inflammation eg increased neutrophils, leukocytes, monocytes, cytokines)
Increased cell tension and strain from oedema and agents, such as prostaglandins and histamine cause pain
Additional muscle tissue breakdown and pain occur due to formation of proteases, phospholipases, and reactive oxygen species.
Cells repair themselves an form protective proteins that prevent muscle soreness during subsequent workouts.
Preventing/Reducing DOMS
- Minimise eccentric work early in training program
- Progressively build volume and intensity
- Warming up, cooling down, and stretching does not prevent soreness
- Suffer early and adapt repeated bout effect
Responses to resistance training
- Adaptations to resistance training are specific to the stimulus
- We can modify the stimulus through load, contraction type, velocity, joint angle, movement pattern
- We can use force-velocity and force-time curves to assess current capabilities and target specific performance improvements
- Adaptations can be neural, myogenic or metabolic
- Early improvements in strength are neural
