ch5 - adaptations to anaerobic training programs Flashcards
(130 cards)
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.
