22 Neural Adaptations to Training.docx

Neural Adaptations to Training

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

      • Demonstrates that early strength gains are mediated by neural adaptions

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

    • Distinct time courses of neural and myofibril adaptations to strenght training

      • 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

Intramuscular coordination (in the muscle itself)

  • Strength training induces adaptations to intramuscular coordination

    • 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

          • Until you are moving 100% of the weight that you can, your motor units will not fire 100% --> training at max requires CNS to remove the “breaks”, so we can increase firing rates to increase force production

      • Submaximal effort strength training – uses load less than 80% of 1RM

        • 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

      • Reflects improvements in performance of specific motor skills

    • Prior experience is associated with differences in intermuscular coordination --> novice vs elite cyclists

    • 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

      • Different muscles exhibit different adaptations

      • WE WILL SEE THIS DIAGRAM ON THE EXAM!!!

Neural adaptations to fatigue – involve both peripheral (muscular) and central (neural) mechanisms, fatigue is a decrease in force production

  • Peripheral fatigue – results from changes to contractile properties of muscles

  • Central fatigue – results from changes to neuromuscular mechanisms

    • Seen in lower firing rates --> neural drive decreases which leads to lower firing of motor neurons

Adaptations of Neuromechanics

  • 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

    • Jumping off a box --> acceleration due to gravity increases load placed on muscles, which increases the eccentric contraction

  • 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 --> improvements in brain health, but not necessarily cognition

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

    • Better mental health in elderly who exercise

    • Better cognition in children who exercise

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

  • Many factors influence brain health and cognition

    • Social interactions --> happen during exercise and play, also important to cognition, so it is hard to control for these

      • Biopsychosocial models --> better explain the positive effects of exercise

  • Animal studies indicate that exercise induces several adaptations

    • Some adaptations that directly improve brain health

      • 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

        • Exercise in Parkinson’s patients has been a huge treatment to help slow down the progression of Parkinson's disease