Bio 252 Laboratory Report

BIO 252 LABORATORY REPORT Activity 3: Recruitment and Contractions Name: Instructor: Date: PREDICTIONS 1. When the arm goes from resting to flexing, the amplitude and frequency of sEMG spikes will: increase 2. During flexion, the amplitude and frequency of sEMG spikes will _be more_ during extension. 3. Recruitment of motor units will be greatest when the load is: 20 MATERIALS AND METHODS Comparison of motor unit activation during muscle tone and concentric and eccentric isotonic contractions 1. Dependent Variable amplitude 2. Independent Variable muscle movement 3. Controlled Variables total motor units present in muscle, subjects physical condition Recruitment during isometric contractions 1. Dependent Variable amplitude and frequency of sEMG spike 2. Independent Variable muscle load 3. Controlled Variables total number of motor units present in a muscle, muscle movement, and subjects physical condition 4. What does the acronym sEMG stand for? Surface Electromyography 5. During a muscle contraction, what is recorded on a sEMG? Amplitude in mV and frequency of sEMG spikes 6. Spike numbers were measured during a 200 msec period. RESULTS See Table 3: Muscle Tone (Resting) and Isotonic Contractions See Graph 1: sEMG Amplitudes and Frequencies at Rest and During Isotonic Contractions 1. When the biceps brachii was at rest, were motor units activated as indicated by amplitude and frequency of sEMG spikes? Motor units were activated at a low rate. This happens because normal resting muscles exhibit muscle tone due to the stimulation of a small number of motor units. The activation of them keeps the motor units and the muscle strong. 2. What was the change, if any, of motor unit stimulation (reflected in amplitude and frequency of sEMG spikes) during concentric contraction against a 5 pound load? There was a change from 0.12 mV to 0.43mV when a five pound load was lifted. 3. Did motor unit stimulation, (reflected in amplitude and number of spikes per 0.2 sec time period) increase, decrease, or not change when biceps brachii went from concentric to eccentric contraction with a 5 pound load? Motor units decrease with amplitude. 0.43 to 0.32mV in an eccentric contraction with a five pound load. sEMG goes up and did not change or move from concentric to eccentric contraction with a 5lb load. 4. Did the arm flex or extend during the eccentric contraction of the biceps brachii? Extends during eccentric contraction See Table 4: Isometric Contractions See Graph 2: sEMG Amplitudes and Frequencies at Rest and During Isometric Contractions under Different Loads 5. Describe how amplitude of sEMG spikes changed with increasing muscle load. First there was a gradual increase in amplitude with increasing the muscle load. Then there was a decrease in amplitude by a little (0.12 mV to 0.087 mV). 6. Describe how frequency of sEMG spikes changed with increasing muscle load. The load started increasing and so did the frequency of sEMG until it reached an optimal level (21 per 0.2 sec) at the 10 lb threshold.