ch5 - adaptations to anaerobic training programs Flashcards
what kind of anaerobic adaptations exist?
changes to the nervous, muscular, connective tissue, endocrine, and cardiovascular systems.
what is the most common kind of anaerobic adaptation study?
in the early to intermediate stages of training (i.e. 4 to 24 weeks)
how is augmented neural drive thought to occur?
via increased agonist muscle recruitment, improved neuronal firing rates, and greater synchronization in the timing of neural discharge during high-intensity muscular contractions; a reduction in inhibitory mechanisms (i.e. from Golgi tendon organs) is also thought to occur with long-term training
where does increased motor unit adaptation begin?
in the higher brain centers, where the intent to produce maximal levels of muscular force and power causes motor cortex activity to increase; as force developed rises, or whenb a new exercise or movement is being learned, primary motor cortex activity elevates in an effort to support the enhanced need for neuromuscular function
where/how are adaptation to anaerobic training methods reflected?
by substantial neural changes in the spinal cord, particularly along the descending corticospinal tracts
how do we know that recruitment of fibers is a limiting factor in strength?
in untrained individuals or in those rehabilitating from injury, electrical stimulation has been shown to be more effective than voluntary activations in eliciting beneficial gains. research has shown that only 71% of muscle tissue is activated during maximal efforts in untrained populations.
what does a motor unit consist of?
the alpha motor neuron and the muscle fibers that it activates; a motor unit may innervate <10 muscle fibers for small, intricate muscles or >100 fibers for large, powerful trunk and limb muscles.
Increased force with greater firing rates reflects what?
the summation of successive muscle contractions, whereby action potentials temporarily overlap
how does summation influence force production?
With increased motor unit firing rates, the muscle fibers are continually activated by subsequent action potentials before they have time to completely relax following a prior action potential. The summation of overlapping action potentials is expressed as augmented contractile strength. These firing rates represent an adaptive mechanism shown to improve following heavy resistance training.
in terms of motor units, what are gains in strength and power of agonist muscles generally associated with?
(a) an increase in recruitment; (b) an increased rate of firing; (c) greater synchronization of neural discharge, which acts to coordinate the activity of multiple muscles in synergy; or (d) a combination of all these factors.
what are motor units high in the recruitment order primarily used for?
high force, speed, or power production
do some muscle fiber types (e.g. type I, II) get larger with resistance training, or all?
all muscle fibers get larger because for the most part they are all recruited to some extent in order to produce the higher levels of force required to lift progressively heavier loads
once a motor unit is recruited, less activation is needed in order for it to be rerecruited. why might this have implications for strength and power training?
the high-threshold motor units may be more readily reactivated subsequent to prior recruitment.
under what circumstances do exceptions to the size principle exist – i.e. an athlete is able to inhibit the lower-threshold motor units and in their place activate higher-threshold motor units?
when force production is required at very high speeds for the expression of muscular power (e.g. olympic weightlifting, plyometrics, agility/interval training)
what is the reasoning behind the selective recruitment principle?
it would be very difficult for athletes to generate enough angular velocity and power to attain maximal height for the vertical jump if they had to recruit the entire slow-twitch motor unit pool before activation of the fast-twitch units (there simply is insufficient time to recruit all of the motor units in order and still perform an explosive jump)
is selective recruitment learned?
selective recruitment appears to be an intrinsic neural mechanism favoring explosive exercise, but using specific training methods may enhance selective recruitment
how does size affect muscle activation?
as muscle size increases it does not require as much neural activation to lift a given load; this shows the importance of progressive overloading to promote the continual recruitment of an optimal amount of muscle tissue
is rate of firing important for muscle adaptation?
yes, high firing rates from the onset of ballistic muscle contraction are especially critical to increased rates of force development, and the increase in firing rate (vs. recruitment) appears to be dependent on muscle size, such that smaller muscles rely more on an increased firing rate to enhance force production whereas larger muscles depend more on recruitment. anaerobic training can play a role in enhancing firing rates of recruited motor units.
how might training improve firing rates?
resistance training may result in a more synchronized pattern (i.e., the firing of two or more motor units at a fixed interval) of activation during the exertion of large forces, rather than the customary asynchronous pattern usually common to motor function; synchronization is potentially more critical to the timing of force production and less significant with regard to the overall level of force developed.
why is the NMJ significant?
it represents another potential site for neural adaptation following anaerobic training – following both high- and low-intensity running, the NMJ was found to increase in its total area. High-intensity training, however, resulted in more dispersed, irregular-shaped synapses and a greater total length of nerve terminal branching compared to low-intensity training. In another study, greater end-plate perimeter length and area, as well as greater dispersion of acetylcholine receptors within the end-plate region, were also found after seven weeks of resistance training. anaerobic training appears to induce beneficial morphological changes in the NMJ that are conducive to enhanced neural transmission capabilities.
how does anaerobic training affect reflex?
causes positive changes in the reflex (i.e., muscle spindle or stretch reflex) response of the neuromuscular system and enhances the magnitude and rate of force development via this reflex. resistance training in particular has been shown to increase reflex potentiation by between 19% and 55%. resistance-trained athletes (weightlifters, bodybuilders) are found to have greater reflex potentiation in the soleus muscle compared to untrained individuals.
what are the types of EMG used and why?
surface EMG and intramuscular (needle or fine wire) EMG
what are the pros/cons of surface EMG?
surface EMG requires placement of adhesive electrodes on the surface of the skin where they are able to monitor a large area of underlying muscle. Surface EMG is often more effective for monitoring superficial muscle, as it is unable to bypass the action potentials of superficial muscles and detect deeper muscle activity. however, the more body fat an individual has, the weaker the EMG signal is likely to be with use of this methodology.
what are the pros/cons of intramuscular EMG?
the skin surface is numbed, and a needle electrode, or a needle containing two fine-wire electrodes, is inserted through the skin and positioned into the belly of the muscle itself. Fine-wire electrodes emphasize a specificity of assessment in that they are located in a muscle of interest and accurately record localized motor unit action potentials (85). Because of its invasiveness, intramuscular EMG is primarily adopted in research settings or under clinical conditions.
what factors confound EMG readings?
not sure if e.g. increased recruitment, discharge rate, or synchronization, or golgi tendon organ inhibition
during what portion of a training program do neural adaptations dominate?
6 to 10 weeks.
do neural adaptations stop if the athlete ‘gets used to’ hypertrophy gains?
no, neural adaptations will contribute to the performance improvements through progressive overload
for what kinds of activities are neural factors most important?
very high training intensities (>85% of 1-repetition maximum [1RM]) and training programs designed to elicit muscular power..
what do EMG studies say about cross-education and how do we know?
strength in the untrained limb may increase up to 22%, with an average strength increase of approximately 8%; the increase in strength of the untrained limb is accompanied by greater EMG activity in that limb, thereby suggesting that a central neural adaptation accounts for the majority of strength gains.
what is the opposite of cross-education?
a bilateral deficit in untrained lifters; force produced when both limbs contract together is lower than the sum of the forces they produce when contracting unilaterally.
what kinds of activities might have neural-limiting cocontraction antagonist muscle group activity?
ballistic movements that require high levels of joint stability, or when people are unfamiliar with a task and require more inherent stability
other than size and fiber type changes, what are the biochemical/ultrastructural components of muscle adaptation?
muscle architecture, enzyme activity, and substrate concentrations
what is the biological process of hypertrophy?
there is an increase in the net accretion (increase in synthesis / reduction in degradation / both) of the contractile proteins actin and myosin within the myofibril, as well as an increase in the number of myofibrils within a muscle fiber. In addition, other structural proteins such as titin and nebulin are synthesized proportionately to the myofilament changes. The new myofilaments are added to the periphery of the myofibril and result in an increase in its diameter. The cumulative effect of these additions is an enlargement of the fiber and, collectively, the size of the muscle group itself.
what pathways does mechanical deformation activate?
the protein kinase B-mammalian target of rapamycin (mTOR) pathway, the adenosine monophosphate activated protein kinase pathway, and the mitogen-activated protein kinase pathway
how does the akt/mTOR pathway directly regulating adaptations to resistance training?
when muscle fibers contract, akt/mTOR signaling increases dramatically, and this response is critical for increasing muscle protein synthesis and subsequent growth (a process known as myogenesis)
what factors influence protein synthetic rates?
carbohydrate and protein intake, amino acid availability, timing of nutrient intake, mechanical stress of the weight training workout, muscle cell hydration levels, and the anabolic hormonal and subsequent receptor response
what is the sequence of protein synthesis?
(a) water uptake, (b) noncontractile protein synthesis, and (c) contractile protein synthesis – and concurrently, reduced degradation acts to maintain the size of fibers by reducing net protein loss
lifting of heavy loads, the inclusion of eccentric muscle actions, and low to moderate training volumes are examples of what?
mechanical factors for hypertrophy
what is the order of most oxidative to least oxidative fibers?
I, Ic, IIc, IIac, IIa, IIax, and IIx, with a concomitant myosin heavy chain (MHC) expression (i.e., MHC I, IIa, and IIx)
how do type IIx change to IIa?
by changing their myosin adenosine triphosphatase (ATPase) isoform content, which then goes to an intermediate fiber Type IIax and then to a IIa
detraining is likely to have what effect on type II fibers?
an increase in Type IIx fibers and a reduction in Type IIa fibers, with a possible overshoot of Type IIx fibers (i.e., higher IIx percentages than observed pretraining)
why is transformation from type II to I probably not possible?
differing MHC isoforms and relative oxidative enzyme content
what effect do larger pennation angles have on protein/CSA?
larger pennation angles can accommodate greater protein deposition and allow for greater increases in CSA
how does anaerobic exercise affect blood pH?
reduces it substantially / acidizes it
how might adaptation affect pH?
more exposure to increased H+ concentration –> buffering capacity can improve –> increased capacity then allows an athlete to better tolerate the accumulation of H+ within the working muscle, resulting in delayed fatigue and greater muscular endurance (HIIT performed above the lactate threshold has been shown to increase buffering capacity by 16% to 38%)
how does CP, ATP, and glycogen content change following resistance training?
study reported 28% increase in resting CP, 18% increase in ATP concentrations and 112% glycogent content after five months of resistance training
axial skeleton is what?
skull-cranium, vertebral column, ribs, and sternum
appendicular skeleton is what?
shoulder girdle, pelvis, and bones of the upper and lower extremities
why is the rate of bone adaptation different in axial vs appendicular skeleton?
differing amounts of trabecular (spongy) bone and cortical (compact) bone
why is trabecular bone able to respond more rapidly to stimuli than cortical?
less dense, greater surface area-to-mass ratio, softer, weaker, more flexible and therefore more inclined to adaptive change
what is the MES for bone adaptation?
approximately 1/10 of the force required to fracture bone.
how does high intensity anaerobics affect collagen?
increase in collagen fibril diameter + number of covalent cross-links within hypertrophied fiber + increase in the number of collagen fibrils + increase in packing density of collagen fibrils
