Muscle Lab EMG Seminar Notes Electromyography EMG EMG

Muscle Lab: EMG Seminar Notes

Electromyography (EMG) • EMG - the electrical activity of the many muscle cells (fibers) controlling the gross anatomical muscle • Recorded by placing electrode on surface of skin

Voluntary Change in Force Increasing the load (# of books) would increase the electrical activity in the muscle, therefore, increase the EMG amplitude

Alternating Activity and Coactivation • Recorded from the triceps and biceps • Note that when the biceps muscle is forcefully activated, there is a minor increase in activity of the triceps co-activation • The effect is to stabilize the joint as the biceps produces the major force of commanded movement

Coactivation

Evoked EMG • Evoked EMG by stimulation of the median nerve • Increased amplitude of EMG as a function of increased stimulus • Also observed latency between stimulus and contraction • Latency = time between the start of the stimulus & start of the evoked response

Evoked EMG and latency

Conduction Velocity • Calculating the conduction velocity requires two bits of information • Distance and time (latency) • Distance between stimulating electrodes to recording electrodes • Time it takes to travel from the stimulus site to the recording site

Stimulation of Median Nerve at Elbow to Determine Conduction Velocity

Conduction Velocity • Range = 1 – 120 m/s • Normally 50 – 60 m/s • Influenced by: Diameter of fiber Temperature Myelinated vs. non-myelinated