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When large fast-twitch motor units are temporarily fatigued, non-fatigue small motor units in the same muscle are impaired for small delicate tasks. Why?

When impulses from the brain comes down, the impulses from interneuron goes to small diameter motor neuron, which are associated with non-fatigue motor units, and large diameter motor neurons, which are associated with fast-twitch motor units. More impulse is necessary to activate the fast twitch-muscles because the larger neurons have higher leak current and capacitance. Thus, we have an ascending activation of muscle units, from least forceful units to most forceful. Now my question is, if the fast-twitch muscle units are fatigued, why cant we perform delicate movement/ task?

Fatigue is mainly caused when the motor unit runs out of ATP. So, is that the bridge between these to things, or is it something else?

Or, is it related to how motor units are used is a fixed ascending order for completing tasks? If so, how?

Thanks for all the help!

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I am finding it difficult to understand what exactly you are trying to ask here. –  WYSIWYG Apr 24 at 3:41
    
When impulses from the brain comes down, the impulses from interneuron goes to small diameter motor neuron, which are associated with non-fatigue motor units, and large diameter motor neurons, which are associated with fast-twitch motor units. More impulse is necessary to activate the fast twitch-muscles because the larger neurons have higher leak current and capacitance. Thus, we have an ascending activation of muscle units, from least forceful units to most forceful. Now my question is, if the fast-twitch muscle units are fatigued, why cant we perform delicate movement/ task? –  WalleXD Apr 24 at 3:55

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