EMG Lab

KNES 461 – Electromyography

Purpose: The purposes of this lab session are to gain familiarity with EMG equipment and data collection, and to explore the EMG of the biceps brachii under different conditions.

Methods: EMG of the biceps brachii will be recorded during 3 separate tasks. An electrode will be placed at the mid-belly of the biceps brachii after the skin has been cleaned and prepared for EMG recordings.

· Experiment 1: EMG/Length-tension relationship: The subject will contract the biceps isometrically while holding a 10lb weight at 30 degrees, 90 degrees, and 120 degrees of elbow flexion verified using a goniometer. Each position will be sampled for 5 seconds while isometric EMG data are sampled.

· Experiment 2: The subject will flex their elbow from full extension to full flexion, and then extend their elbow from full flexion to full extension while recording biceps brachii EMG.

· Experiment 3: The elbow will be maintained at 90 degrees and the subject will support weights of 2 lbs, 5 lbs, and 10 lbs while isometric EMG data are sampled.

Results:

Experiment 1: Record the peak EMG amplitude for each angle in the table below (6 points)

30 deg	90 deg	120 deg
37%	22%	58%

Experiment 2: Record the peak EMG amplitude for the concentric and eccentric action in the table below (4 points)

Concentric	Eccentric
62%	44%

Experiment 3: Record the peak EMG amplitude for each weight in the table below (6 points)

2 lbs	5 lbs	10 lbs
		46%

· For Experiment 3: No weight = 14% (Just no weight and 10lbs weight)

Discussion Questions:

1. What is the effect of joint angle on EMG for a constant joint load? What does this tell you about the mechanical and neural contributions to muscle force at different joint positions? (8 points)

2. What is the effect of contraction type on EMG amplitude? What does this tell you about the mechanical and neural contributions to muscle force during different types of muscle contraction? (8 points)

3. What is the effect of increasing load on EMG amplitude for a constant joint angle? There should be a linear relationship between EMG amplitude and load under isometric conditions. Why is this true for isometric actions, but not concentric or eccentric actions? Is EMG amplitude synonymous with muscle force? Why or why not? (8 points)