Lab Arm stuff

Laboratory Report LABORATORY REPORT Activity: Recruitment and Isotonic and Isometric Contractions Name: Uwagboi Divine Instructor: Catherine Hart Date: 03.10.2023 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 ___ during extension. be greater than 3. Recruitment of motor units will be greatest when the load is 20 pounds Materials and Methods Comparison of motor unit activation during muscle tone and concentric and eccentric isotonic contractions 1. Dependent Variable amplitude and frequency of sEMG spikes 2. Independent Variable muscle movement 3. Controlled Variables total number of motor units present in muscle, muscle load, subject's physical condition Recruitment during isometric contractions 1. Dependent Variable amplitude and frequency of sEMG spikes 2. Independent Variable muscle load 3. Controlled Variables total number of motor units present in muscle, muscle movement, subject's physical condition 4. What does the acronym sEMG stand for? Surface Electromyography 5. During a muscle contraction, what is recorded on a sEMG? Amplitude (mV) and frequency of sEMG spikes (motor unit action potentials). 6. Spike numbers were measured during a ____msec period. 200 Results Table 3. Muscle Tone (Resting) and Isotonic Contractions Amplitude (mV) Frequency of Spikes (number per 0.2 msec sampling period) Rest Concentric Eccentric Rest Concentric Eccentric Subject 1 0.12 0.45 0.32 1 20 19 Laboratory Report/ Uwagboi Divine/ Recruitment and Isotonic and Isometric Contractions/ Catherine Hart/ 03.10.2023/ Page [1] of [4]

Laboratory Report Amplitude (mV) Frequency of Spikes (number per 0.2 msec sampling period) Rest Concentric Eccentric Rest Concentric Eccentric Subject 2 0.11 0.44 0.39 1 20 20 Subject 3 0.12 0.47 0.32 1 19 19 average 0.12 0.45 0.34 1 20 19 Graph 1. sEMG Amplitudes and Frequencies at Rest and During Isotonic Contractions Amplitude (mV) 0 0.1 0.2 0.3 0.4 0.5 1 2 3 1. Rest 2. Concentric 3. Eccentric Frequency (spikes number per 0.2 sec time period) 0 5 10 15 20 25 1 2 3 1. Rest 2. Concentric 3. Eccentric 1. When the biceps brachii was at rest, were motor units activated as indicated by amplitude and frequency of sEMG spikes? Yes, at a very low rate (0.12 mV) normal resting muscles exhibit muscle tone due to the stimulation of a small number of motor units. This activation keeps all the motor units. 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? it changed from 0.12 mV at resting to 0.45 mV during a concentric contraction against a 5-pound load. For the frequency of sEMG spikes, there was an increase from 1 (rest) to 20 for the 5-pound load. 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? it decreased. it went from 0.45 mV in a concentric contraction to 0.34 mV in an eccentric contraction with a 5-pound load. for the frequency, it went from 20 to 19. 4. Did the arm flex or extend during the eccentric contraction of the biceps brachii? The arm kind of extended during the eccentric contraction. Table 4. Isometric Contractions Isometric Contraction (Amplitudes (mV)) Rest 0 lb 2 lb 5 lb 10 lb 20 lb Subject 1 0.12 0.084 0.185 0.220 0.470 1.270 Subject 2 0.11 0.082 0.170 0.220 0.450 1.270 Subject 3 0.12 0.091 0.162 0.240 0.430 1.240 average 0.12 0.086 0.172 0.227 0.450 1.260 Frequency of Spikes (number per 0.2 msec sampling period) Rest 0 lb 2 lb 5 lb 10 lb 20 lb Subject 1 1 16 16 20 19 19 Subject 2 1 16 17 20 20 21 Laboratory Report/ Uwagboi Divine/ Recruitment and Isotonic and Isometric Contractions/ Catherine Hart/ 03.10.2023/ Page [2] of [4]

Laboratory Report 3. Discuss how increasing the number of motor units stimulated affects force. Depending on the physical activity that needs to be performed, different types of motor units in a muscle are recruited in a specific order. The slow oxidative fibres are activated when weak contractions are required to perform a task. In order to provide more force, fast oxidative– glycolytic fibres are stimulated. Maximum force occurs when all motor units of muscle are stimulated and all muscle fibres are contracting. 4. Discuss how increasing frequency of motor unit stimulation affects force. muscle tension developed by a contracting muscle is determined by the frequency of stimulation of motor units and the number of motor units stimulated. An increase in the frequency of muscle stimulation increases force production. Muscle tension depends upon the frequency of stimulation of the motor unit and the number of motor units stimulated 5. During arm flexion, what type of contraction would the triceps brachii be exhibiting: concentric isotonic contraction, eccentric isotonic contraction, isometric contraction. eccentric isotonic contraction 6. During arm extension, what type of contraction would the triceps brachii be exhibiting: concentric isotonic contraction, eccentric isotonic contraction, isometric contraction. concentric isotonic contraction 7. As muscle load is increased, which muscle fiber type is recruited first, second, and last? The first muscle fibre type is the slow oxidative, the second type is the fast oxidative-glycolytic, and the last type is the fast glycolytic fibres. 8. Describe the importance of this order. Include affect on force of contraction and fatigue. The force generated increases as the number of motor units contracts at the same time. After long periods of muscle contraction muscle fatigue sets in. The muscle cannot maintain the force of contraction. Fatigue results mainly from changes within the muscle fibres 9. Restate your predictions that were correct and give data from your experiment that support them. Restate your predictions that were not correct and correct them, giving with supporting data from your experiment that supports your corrections. My predictions were correct. When the arm goes from resting to flexing, the amplitude and frequency of sEMG spikes will: increase. It went from 0.12 to 0.45 mV and from 1 to 20 per 0.2 msec. for my second prediction during flexion, the amplitude and frequency of sEMG spikes will be greater than during extension. It went from 0.45 to 0.34mV, but the frequency of spikes stayed the same (20 per 0.2 msec) Application 1. Flaccid muscles do not exhibit muscle tone. Explain how muscles become flaccid. Muscles become flaccid as a result of damaging the motor neurons that serve the skeletal muscle. motor neurons are damaged or cut, then a state of limpness occurs and the muscle loses tone. 2. In the experiment "Muscle Tone and Concentric and Eccentric Isotonic Contractionsa", the muscle contracts isometrically prior to the concentric isotonic contraction. A muscle that contracts isometrically maintains the same length, but its tension increases. Its length remains fixed, but its tension increases. If movement occurs, then the muscle shortens and we get a concentric isotonic contraction 3. Explain why the muscle contracts isometrically before it shortens. The nerve that innervates the biceps brachii muscle is the musculocutaneous nerve. Explain what effect damage to this muscle would have on contractile force and recruitment of motor units in the biceps brachii muscle. If the musculocutaneous nerve is damaged, it will affect the ability of the biceps brachii muscle to perform different functions, resulting in muscle weakness, poor muscle tone, sensory loss, or a weak or absent biceps tendon reflex. Laboratory Report/ Uwagboi Divine/ Recruitment and Isotonic and Isometric Contractions/ Catherine Hart/ 03.10.2023/ Page [4] of [4]