Which Factors Contribute to Force Production? (Part 3 and 4)

3. Neural Factors

3.1. Motor Unit Recruitment

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Motor Units (MUs) are generally recruited in a orderly fashion: Slow MUs to Fast MUs. This is stated by the Henneman Principle. If a task does not require all MUs to be recruited, low threshold MUs will be called into action. However, if slow/low threshold MUs are not enough to complete a task, fast/high threshold MUs need to be recruited. Obviously, this mechanism takes time to be performed, and the time needed to recruit high threshold MUs appears to be modifiable up to a certain point depending on training strategies.

3.2. Firing Frequency

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In order to have a muscle action, electrical impulses need to be sent to muscle fibers. The mechanism behind this process is the ALL OR NOTHING law. It states that a single twitch is always sent at its maximum capacity. What changes the degree or intensity of a muscle action is the frequency of those twitches are sent. When firing frequency is high, a state of tetanus occur, resulting in maximal activation of MUs. Firing Frequency can be increased through strength/power training, resulting is increases in Rate of Force Development (RFD).

3.3. Motor Unit Synchronization

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As we saw before, within the same muscle there are different fiber types. Additionally, there are also dozens to thousands of different MUs within each individual muscle (intramuscular). As we saw with Hennrman Principle, MUs are recruited according to the task demands and MUs threshold. The synchtonization of MUs enables in more coordinated MUs activation for a certain muscle, resulting in more efficient muscle action with greater potential to produce force.

3.4. Intermuscular Coordination

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3.4.1 .Activation of Synergists

As we saw with intramuscular coordination and MUs synchronization, the ability to synchronize synergistic muscles is crucial for performance, and it is a result of motor learning.

3.4.2. Co-Activation of Antagonists

Activation of antagonist muscles have a negative effect over concentric ballistic performance. Untrained subjects show a higher co-activation of antagonists, and one of the most pronounced intermuscular adaptations after ballistic training is its decrease, resulting in performance enhancement.

4. Muscle Environment

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Fatigue, Muscle Temperature and Hormonal Concentrations can negatively affect muscle force production

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