User:Laurenlacey223/sandbox



Neuromechanical Traits of Different Athletes

Different athletes possess particular neuromechanical traits to assist them to excel in a physical activity. Their neuromechanical attributes can be understood by researching their muscle, neuron, and motor unit traits. An athlete's neuromechanical traits maybe correlated with the athlete's specialized sport, such as sprint or endurance locomotion.

=Muscle=

Fiber Type Composition
Muscles are comprised of three types of muscle fibers Type I, Type IIA, and Type IIB. Type I muscle fibers are known as "slow twitch oxidative", Type IIA are "fast twitch oxidative" and Type IIB are "fast twitch glycolytic".

Type I muscle fibers are more efficient in using oxygen to generate more ATP which helps extend muscle contractions over a long period of time and in return are less susceptible to fatigue. Type I fibers are activated slowly and generate low force and power. Endurance athlete muscles will usually compromise of more Type I muscle fibers than Type II muscle fibers.

Both Type II muscle fibers are activated quickly and generate short bursts of speed and strength. Type IIA muscle fibers are less susceptible to fatigue than Type IIB. Also Type IIB fibers are able to contract faster than Type IIA. Sprint athlete muscles will usually compromise of a larger percentage of Type II muscle fibers than endurance athlete muscles because sprinters need to quickly generate a large quantity of force and power.

Fatigue
Muscular fatigue is highly related to the fiber composition of the muscle. Endurance athletes typically have a high oxidative capacity in their muscles. A high oxidative capacity is linked with a high potential to recover from an exercise. In general endurance athletes have a very good maximal oxygen uptake. On the other hand, sprint athletes have high glycolytic potential and are more susceptible to fatigue.

Endurance athletes maintain a lower blood lactate concentration than sprint athletes during aerobic power tests and anaerobic power tests. This suggests that endurance athletes are able to recover faster than sprint athletes when subjected to the same exercise.

=Neuron=

Motorneuron Excitability and Stretch Reflex Response
Motorneuron excitability is commonly assessed using the H-reflex. The H-reflex is a monosynaptic reflex response analogous to the tendon reflex as the peripheral nerve is excited by electrical stimulation. Power or anaerobic trained athletes have decreased resting H-reflexes relative to endurance or aerobically trained athletes.

Stretch reflex response is normally assessed by measuring the muscle contraction using electromyography signals after a resting tendon tap has been performed. A greater resting reflex response has been observed in elite sprint athletes than elite endurance athletes. Stretch reflexes are either unaffected or increased after sprint activity which indicates an increase in muscle spindle sensitivity to compensate for the decreased motorneuron excitability.

Fatigue
Neural fatigue is defined as the involuntary reduction to voluntary activation. The source of neural fatigue is much debated however some possibilities include: depression of motorneuron excitability, segmental afferent inhibition, and supra-spinal failure. Neural fatigue can occur during and immediately after exercise as well as minutes to days after exercise. Neural fatigue which occurs during and immediately after is known as acute neural fatigue and neural fatigue which occurs minutes to days after is known as long lasting neural fatigue.

Although the cause of acute neural fatigue is not known, research suggests that acute neural fatigue maybe caused by peripheral mechanisms rather than central mechanisms. As an athlete increases running speeds their muscle activity or EMG activity also increases. Therefore, at high speeds the nervous system must recruit more muscle activity which in return is most stressful.

Long lasting neural fatigue is probably due to muscle damage that affects neural function. Muscle damage can occur in any athlete even well training athletes. During sprint activity Type II muscle fibers are the most likely to obtain damage. Muscle damage can affect reflex response and muscle activation due to chemical agents related to muscle pain.

=Motor Unit Recruitment= Muscle fibers are recruited voluntarily and involuntary by nerve impulses sent from descending responses from the brain, sensory feedback reflexes, and the central pattern generator. Muscle fibers are grouped into motor units, which are comprised of the same type of muscle fiber. Nerves are connected to a group of motor units which cause the motor units to activate. Fast twitch motor units are controlled by fast twitch nerves and slow twitch motor units are controlled by slow twitch nerves.

The ability to fully or selectively recruit certain motor units has been studied many times. The body normally restricts the recruitment of muscle fibers, so an individual is not able to recruit all muscle fibers at once. However, with training, athletes have been able to become more efficient at motor unit recruitment. Sprint athletes are able to synchronize their timing of slow and fast twitch neuromuscular recruitment so they are able to output higher force, power, and speed. In a study it was demonstrated that sprint athletes have a significantly greater ability to selectively recruit fast twitch motor units compared with endurance athletes. With training endurance athletes are able to restrict their muscle recruitment to efficiently timing the use of their muscle fibers to sustain long periods of muscle activation.

=See also=
 * Muscle weakness
 * Sprint (running)
 * Long-distance running
 * Motor unit
 * Motor unit recruitment
 * Skeletal striated muscle
 * H-reflex
 * Locomotion

= References =

=External links=
 * Understanding Muscle Fiber Type
 * ‘LOCOMOTION NEUROMECHANICS’ course APPH 6232 at Georgia Institute of Technology
 * Fast and Slow Twitch Muscle Fibers