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KINE 3301 Biomechanics of Human Movement. EMG & Motor Neurons. Chapter 18. Motor Unit. A motor unit is one alpha motor neuron and all of the muscle fibers it innervates. EMG Differential Amplifier.
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KINE 3301 Biomechanics of Human Movement EMG & Motor Neurons Chapter 18
Motor Unit A motor unit is one alpha motor neuron and all of the muscle fibers it innervates.
EMG Differential Amplifier The EMG amplifier takes the difference between the muscle fiber action potential from each electrode.
Synchronization Causes Amplification & Cancellation • Synchronization of two muscle fiber action potentials with the same polarity causes amplification. • Synchronization of opposite polarity causes cancellation.
Muscle Twitch Response Stimulation of a motor neuron with a single impulse causes a twitch response.
Stimulation Rate and Tetanic Contractions • Increasing the stimulation rate (firing rate) causes a stair-stepping effect of force. • Maximal stimulation produces a tetanic contraction.
EMG & MU Properties EMG, nerve conduction velocity, firing rate ranges, twitch responses and fatigue curves by motor unit type.
EMG – Force Data Collection Instrumentation used to study muscle force-velocity and force-length relationship.
Ramp Contraction • In a ramp contraction motor units are recruited according to size (ST, INT, FT). • A newly recruited unit fires slower than currently active unit. • Motor Units are recruited and de-recruited at the same force threshold.
Ballistic Contraction The subject is instructed to generate maximum force as rapidly as possible. Theoretically all motor units are recruited simultaneously and each fires at it’s maximal rate at the outset.
Effects of Rate of Force Development on Recruitment & Firing Rate • On the left the subject is instructed to generate a 50% MVC as rapidly as possible. • On the right the subject is instructed to generate a 50% MVC in 2 sec.
