22 Neural Adaptations to Training.docx

Practice

Aimed at improving movement production and information processing used to perform motor skills

• Primarily involves neural adaptations (plasticity)

• Can also induce muscular and metabolic adaptations

Training

Aimed at improving physiological functioning and physical abilities involved in performing motor skills

• Primarily involves muscular and metabolic adaptations 

• Can also induce neural adaptations (plasticity)

Strength training

• Induces myofibril, metabolic, and neural adaptations

  • Neural adaptations account for most early strength gains (first 4 weeks)

Cross-transfer of strength

Refers to the strength gains in an untrained limb following unilateral strength training of the opposite limb

• Early strength gains cannot be explained by myofibril adaptations (hypertrophy)

Distinct time courses of neural and myofibril adaptations to strength training

• Neural adaptations

• Myofibril hypertrophy

• Neural adaptations persist at later times

Neural adaptations

Occur early, within 2 weeks, underlie early strength gains

Myofibril hypertrophy

Occurs later, after 2-4 weeks, underlies later strength gains

Neural adaptations persist at later times

Conflict with traditional views of neural adaptations (used to think these adaptations kind of plateaued), leads to greater specificity of strength gains

Strength training induces adaptations to…

intramuscular coordination (in the muscle itself)

Firing rates of motor units exhibit lower variability

Results in decreased variability of force output, enables better control of movements

Adaptations of intramuscular coordination vary based on type of strength training

Nervous system adapts to the SPECIFIC type of training

Maximal effort strength training

• Uses loads GREATER 80% of 1RM

  • Earlier recruitment of large motor units (still follows size principle)

  • Increased maximal firing rates of most motor units

Submaximal effort strength training

• Delayed recruitment of larger motor units that fatigue quickly 

• Higher firing rates of smaller motor units that are fatigue resistant 

Intermuscular Coordination (between muscles fibers)

Training commonly induces adaptations to intermuscular coordination

Adaptations to the timing of muscle activations

Results in changes to the onset, end, and/or duration of muscle activation

Adaptations to the magnitude of muscle activation

Results in changes to the mean and/or peak amplitude of muscle activations

Agonist and antagonist muscles exhibit less co-contraction

Increases in agonist activation and/or decreases in antagonist activation

Intermuscular coordination adaptations…

Exhibit SPECIFICITY to the motor skills used for training

Training induces specific adaptations to intermuscular coordination

• Changes to onset and duration of muscle activation

• Changes to mean and/or peak magnitude of muscle activations 

• Agonists and antagonist muscles exhibit less co-contraction

Neural adaptations to fatigue

involve both peripheral (muscular) and central (neural)

Peripheral fatigue

Results from changes to contractile properties of muscles 

Central fatigue

Results from changes to neuromuscular mechanisms

High-load strength training

• Training greater than 80% of 1RM, induces altered neuromechanics

  • Large forces from loading induces greater muscle-tendon stiffness

    • Leads to increased power amplification (storing power in tendons and connective tissues to later release it) due to greater force transmission

    • Induces neural adaptations that improve neuromuscular adaptations

Plyometric training

Uses stretch-shorten cycle to alter neuromechanics

• Stretch-shorten cycle creates large forces that increase muscle-tendon stiffness

  • Leads to increased power amplification due to greater force transmission

  • Induces neural adaptations that improve neuromuscular mechanisms

Flexibility training

• uses stretching exercises, can improve musculoskeletal disorders, may prevent muscle-tendon injuries, may help maintain muscle health

  • Flexibility training may alter neuromechanics

    • Can decrease muscle-tendon stiffness 

    • May diminish strength and power by reducing power amplification

    • ***Based on studies of excessive stretching that may not apply to normal stretching

    • Combining flexibility and strength training may prevent decreases in muscle-tendon stiffness

Exercise and Brain Health

• Many studies provide evidence that exercise is associated with better brain health and cognition 

• Lack evidence for a causal relationship --> difficult to design quality of RCTs in humans, evidence is not strong yet

Social interactions

happen during exercise and play, also important to cognition, so it is hard to control for these

Biopsychosocial models

Animal studies indicate…

that exercise induces several adaptations

• Improved neural plasticity 

• Increased neurogenesis (extent to this in humans is unknown in general)

• Increased blood flow

• Increased neurotrophic factors (play a role in plasticity and neuron health)

Other adaptations inhibit factors that negatively affect brain health…

• Decreased neuroinflammation

• Decreased neurodegeneration