Adaptations to Resistance Training

What are some examples of sports that resistance trained was initially confined to?

football and track and field

What has research over the last 30 years demonstrated in regards to resistance training?

-the value of it for overall health, fitness, and in rehab settings

-everyone should do some resistance training unless contraindicated

After 3-6 months of resistance training how will untrained individuals benefit?

-may achieve 25%-100% of strength gains

-both neurological and skeletal muscular adaptations

What can account for up to 50% of early strength gains in untrained individuals?

learning effect (synchronicity of firing)

In resistance training, what do early and later strength gains result from?

-early = more neuromuscular adaptations

-later = more hypertrophy

What population has greater absolute gains?

young men than for young women, older men, or children

What does it mean for muscle to have great plasticity?

can adapt very rapidly and has a lot of potential to train

How are increases in strength related to hypertophy?

increase in strength can occur independently of increases in hypertrophy

What explains the phenomenon that increase in strength can occur independently of increases in hypertrophy?

neuromuscular adaptations

What results in strength gains? (2)

• increase in muscle size (hypertrophy)

• altered neural control

What can strength gains not occur without?

neural adaptations

Can strength gains occur without hypertrophy?

yes; strength is a property of the motor system (CNS & PNS) not just of muscle

What neural adaptations can contribute to strength gains?

-motor unit recruitment

-stimulation frequency (rate coding)

-autogenic inhibition

-altered co-activation

How are motor units typically recruited without training?

-motor units typically recruited asynchronously

-limited number of working fibers during muscle contraction

What is the purpose of a limited number of working motor units in fibers during muscle contraction?

prevent fatigue in untrained muscles

What is the synchronous recruitment mechanism of muscle strength gain that occurs with resistance training?

-synchronous recruitment of motor units results in strength gains

-facilitates a stronger contraction by recruiting more fibers at the same time (increases cross-bridge formation leading to stronger power stroke)

How does synchronicity of motor units result in strength gains?

produces more forceful contraction and improves rate of force development

How are motor units typically recruited?

small (type 1) recruited first followed by progressively larger (type IIa and type IIx) more forceful but less fatigue-resistant fibers

What must typically occur for higher-threshold motor units to be recruited?

typically to recruit higher-threshold MU, lower-threshold MU must be recruited first

How can resistance training affect the recruitment of motor units?

-strength trained individuals can recruit larger MU earlier resulting in greater force production

-strength gains may also result from greater motor unit recruitment

How does strength training result in greater motor unit recruitment?

-increase neural drive during max contraction (trained muscles generate a given force with less EMG activity

-increase frequency of neural discharge (rate coding)

-decrease in inhibitory impulses from spinal cord

What does less EMG activity at a given force indicate?

since EMG activity increases as more MU are recruited, less activity at a given force indicates an individual can recruit higher threshold MU earlier

Ultimately, what leads to strength gains in resistance training?

combination of improved motor unit synchronization and greater motor unit recruitment

Does rate coding increase specifically via rapid-movement, ballistic-type training?

limited evidence to suggest this

What is responsible for autogenic inhibition in muscles?

GTOs

What is autogenic inhibition?

-normal intrinsic inhibitory reflex

-inhibit muscle contraction if tendon is too high

Why is autogenic inhibition important?

prevent muscle damage

How is autogenic inhibition contribute to strength gains?

-less GTO activity in trained muscle

-muscle can generate more force

What aids in joint stability with resistance training?

co-contraction of antagonist muscles

How does reduced co-activation contribute to strength gains?

-trained individuals display less co-activation (co-contraction) of antagonist muscles)

-results in more forceful contractions

-joints in trained individuals are more stable via stronger ligaments and tendons

How does chronic resistance training affect ACh?

enhances both release and sensitivity to ACh

What neuromuscular junction remodeling occurs in response to resistance training?

-increased branching of presynaptic neurons

-more vesicles

-more ACh receptors

-fewer fibers per motor unit in FG fibers (more oxidative)

What is hypertrophy?

increase in muscle size

What are the two types of hypertrophy that may occur?

transient and chronic

When does transient hypertrophy occur?

-after exercise bout

-gone within hours

What causes transient hypertrophy?

due to edema formation from plasma fluid

What results in chronic hypertrophy (long term)?

structural change in muscle

What maximizes chronic muscle hypertrophy?

-high-velocity eccentric training which disrupts sarcomere Z-lines (protein remodeling)

-concentric training alone may limit muscle hypertrophy and strength gains

What intensities can stimulate chronic muscle hypertrophy?

-intensities as low as 30% 1RM and as high as 90-100% 1RM

-caused by both high-rep (low load) and low-rep (high-load) training

-important to train to volitional fatigue/failure

What are the mechanisms that result in fiber hypertrophy?

-more myofibrils

-more actin, myosin filaments (sarcomeres)

-more sarcoplasm

-more connective tissue

What does more actin and myosin as a result of fiber hypertrophy allow for?

more cross-bride cycling which allows for more force

What does fiber hypertrophy allow for?

more storage of muscle glycogen

How does resistance training impact protein synthesis?

increases it

How does protein synthesis change during and after exercise?

-during: synthesis decreases, degradation increases

-after: synthesis increases, degradation decreases

What facilitates fiber hypertrophy?

testosterone

What is testosterone?

natural anabolic steroid hormone

What can synthetic anabolic steroids result in?

large increases in muscle mass

What hormones play a role in hypertrophy?

-testosterone

-growth hormone

-insulin-like growth factor 1 (IGF-1)

When are hormones specifically related to hypertrophy elevated?

post exercise

Are elevated levels of hormones related to hypertrophy needed for anabolism and strength gains?

no

What is fiber hyperplasia?

increase in number of fibers

What is most muscle hypertrophy due to?

fiber hypertrophy NOT fiber hyperplasia

Can fiber hyperplasia contribute to muscle hypertrophy?

yes but not through cell division, only through satellite cell function

What fiber type hypertrophy does high intensity training mainly cause?

type II fiber hypertrophy

What does fiber type hypertrophy vs. hyperplasia depend on?

resistance training intensity or load

What are satellite cells?

myogenic stem cells involved in skeletal muscle regeneration

What activates satellite cells?

stretch and injury

What is the benefits of satellite cells?

-after activation they proliferate, migrate, and fuse with muscle fiber

-provide additional nuclei for muscle fibers

-added DNA is necessary for additional protein synthesis used in muscle growth and repair

In regards to satellite cells, when will hypertrophy occur?

when they fuse with muscle fibers

In regards to satellite cells, when will hyperplasia occur?

limited evidence suggests satellite cells may fuse with other satellites to form a new muscle fiber (hyperplasia)

What factors are critical in the first 8-10 weeks of strength gains?

neural factors

What occurs in the initial (short-term) strength gains?

substantial increase in 1RM due to increase in voluntary neural activation

What factors are critical in strength gains after 10 weeks?

hypertrophy

What occurs in the long-term strength gains?

-associated with significant fiber hypertrophy

-net increase in protein synthesis requiring time to occur

What results in atrophy?

reduction or cessation of activity that leads to change in muscle structure and function

What studies were used to investigate atrophy?

-limb immobilization

-detraining

-astronaunts

What protein breaks down tissue in atrophy?

proteolysis

In immobilization, how soon can muscle changes be seen?

after 6 hours

What results in atrophy in immoblilization?

lack of muscle use leads to reduced protein synthesis which initiates the process of muscle atrophy

In the first week of immobilization what occurs?

-strength loss of 3-4% per day

-decrease size (atrophy)

-decrease neuromuscular activity

What fiber type is more affected by immobilization and atrophy?

type I

What are the reversible effects of immobilization and atrophy on type I and type II fibers?

-cross-sectional area decreases

-cell contents degenerate

How soon can lost strength from detraining be regained?

6 weeks (new 1RM matches or exceeds old 1RM)

What prevents detraining once a training goal is met?

maintenance resistance program (maintains strength and 1RM but reduces training frequency)

Even though training regimen may not outright change fiber type, what fiber changes can occur with aerobic and anaerobic training?

-type II fibers may become more oxidative with aerobic training

-type I fibers may become more anaerobic with anaerobic training

What conditions is fiber type conversion possible?

-cross-innervation (both directions)

-chronic low-frequency stimulation (type II to I in rat research)

-high intensity treadmill or resistance training (possibly type 1 to type IIa)

What is cross innervation (used in labs)?

using a type 2 MU to innervate type I fibers and vice versa

What fiber type change is common with resistance training?

type IIx to type IIa

What fiber type change may occur with detraining?

transition back to type IIx from IIa

What did a 20-week heavy resistance training program find?

-static strength and cross-sectional area increased

-percent of type IIx decreased and percent of type IIa increased

Although very few, what studies have shown type I to type IIa fiber type transitions?

high intensity resistance work plus short-interval speed work

How much protein is optimal to consume after resistance exercise for muscle growth?

20-25g

What is the affect of resistance training on protein synthesis?

RT increases protein synthesis

What is the optimal timing for consumption of protein after resistance training?

-"golden hour"

-anabolic window 60-90 min is optimal

-may also depend on intensity/duration of exercise

-distributing intake before and after training may give similar results

How much protein should athletes consume per day to increase muscle mass?

1.6-1.7 grams of protein per kg body weight

When are small and large doses of protein intake recommended for protein synthesis?

-small doses (20g) every 2-3 hours

-larger doses (20-25g) recommended immediately after RT

Besides proteins, what else should be consumed post-training?

carbs for glycogen storage

What is the role of histamine in post-exercise hypotension?

helps cause post-exercise vasodilation

What is insulin sensitivity?

how much glucose uptake from blood to muscle per unit of insulin secreted by beta cells

Consumption of what results in better glycogen repletion post-exercise?

carbs AND proteins

How does exercise impact insulin sensitivity and what population may benefit from this?

exercise increases insulin sensitivity; diabetics may benefit from this

What enzyme controls protein synthesis?

enzyme mTOR (mechanistic target of rapamycin)

What activates mTOR?

mainly by muscle stretch (ex. RT), but also insulin and amino acids (leucine)

What amino acid is seen in a lot of supplements and is geared towards increase in muscle mass?

leucine

What type of hormone is insulin?

fed hormone (released to increase storage and growth)

What does the activation of mTOR result in?

-activates transcription of mRNA

-increases synthesis of ribosomes

What was the traditional concern for resistance training in children?

unsafe due to growth plate concerns, especially prior to hormonal changes found in puberty

What is the current general consensus on resistance training in children?

RT can be a safe and effective method of conditioning for children if properly implemented (use ACSM, NSCA, Academy of Pediatrics, NATA guidelines)

What is the minimum age requirement to start resistance training in children?

no minimal age requirement, but if the child is ready for sports, they are ready for some types of RT

What should the primary emphasis with resistance training be for youth?

-enjoyable

-technique

-use principle of specificity