The Effect of Stimulus Frequency on Skeletal Muscle Contraction

PhysioEx Lab Report Exercise 2: Skeletal Muscle Physiology Activity 3: The Effect of Stimulus Frequency on Skeletal Muscle Contraction Name: Date: 15 September 2020 Pre-lab Quiz Results You scored 100% by answering 4 out of 4 questions correctly. 1 During a single twitch of a skeletal muscle You correctly answered: maximal force is never achieved. 2 When a skeletal muscle is repetitively stimulated, twitches can overlap each other and result in a stronger muscle contraction than a stand-alone twitch. This phenomenon is known as You correctly answered: wave summation. 3 Wave summation is achieved by You correctly answered: increasing the stimulus frequency (the rate of stimulus delivery to the muscle). 4 Wave summation increases the force produced in the muscle. Another way to increase the force produced by a muscle is to You correctly answered: increase the number of activated motor units. Experiment Results Predict Questions 1 Predict Question 1: As the stimulus frequency increases, what will happen to the muscle force generated with each successive stimulus? Will there be a limit to this response? Your answer: As the stimulus frequency increases, the muscle force generated by each successive stimulus will increase. There will be a limit to this increase. 2 Predict Question 2: In order to produce sustained muscle contractions with an active force value of 5.2, do you think you will need to increase the stimulus voltage? Your answer: No. Stop & Think Questions 1 Was there any change in the force generated by the muscle during the second stimulated twitch? You correctly answered: Yes, the second twitch generated more muscle force. 2 Is the total muscle force generated by the higher frequency stimulation greater than the force generated in previous stimulations? You correctly answered: Yes, it is greater than the previous stimulations. 3 Does the force generated by the muscle change with each additional stimulus? You correctly answered: As the stimulus frequency increased, the muscle tension generated by each successive stimulus also increased, and a limiting maximum value was observed. Experiment Data Voltage (v) Length (mm) Stimulus Active Force Passive Force Total Force 8.5 75 Single 1.83 0.0 1.83 8.5 75 Multiple 2.87 0.0 2.87 8.5 75 Multiple 2.90 0.0 2.90 8.5 75 Multiple 4.61 0.0 4.61 10 75 Multiple 4.12 0.0 4.12 8.5 75 Multiple 3.33 0.0 3.33 Voltage = 8.5 V Single Stimulus Active Force = 1.83 Voltage = 8.5 V Multiple Stimulus Active Force = 2.87 Voltage = 8.5 V Multiple Stimulus Active Force = 2.90 Voltage = 8.5 V Multiple Stimulus Active Force = 4.61 Voltage = 10 V Multiple Stimulus Active Force = 4.12 Voltage = 8.5 V Multiple Stimulus Active Force = 3.33 Post-lab Quiz Results You scored 100% by answering 4 out of 4 questions correctly. 1 Which of the following is by a skeletal muscle? not one of the ways that the body can increase the force produced You correctly answered: application of higher voltages to the whole muscle. 2 When a muscle receives a stimulus frequency that causes non-overlapping each other closely in time such that the peak tension of each twitch rises in a stepwise fashion up to a plateau value, the result is known as You correctly answered: treppe. 3 In this experiment the isolated skeletal muscle was repetitively stimulated such that individual twitches overlapped with each other and resulted in a stronger muscle contraction than a standalone twitch. This phenomenon is known as twitches to follow You correctly answered: wave summation. 4 Wave summation is achieved by You correctly answered: increasing the rate of stimulus delivery (frequency) to the muscle. Review Sheet Results 1 What is the difference between stimulus intensity and stimulus frequency? Your answer: Stimulus frequency refers to the amount of times the stimulus intensity (low/moderate/high) is applied to the muscle. 2 In this experiment you observed the effect of stimulating the isolated skeletal muscle multiple times in a short period with complete relaxation between the stimuli. Describe the force of contraction with each subsequent stimulus. Are these results called treppe or wave summation? Your answer: These are called wave summation, because there is a noted increase in frequency, which resulted in an increased in the force produced by the entire muscle. 3 How did the frequency of stimulation affect the amount of force generated by the isolated skeletal muscle when the frequency of stimulation was increased such that the muscle twitches did not fully relax between subsequent stimuli? Are these results called treppe or wave summation? How well did the results compare with your prediction? Your answer: You must increase the frequency of the stimulus stimulus to both to reach. 4 To achieve an active force of 5.2, did you have to increase the stimulus voltage above 8.5 volts? If not, how did you achieve an active force of 5.2? How well did the results compare with your prediction? Your answer: No, the voltage remained the same through my predications. The stimulus had an increased frequency at which it stimulated the muscle fiber. 5 Compare and contrast frequency-dependent wave summation with motor unit recruitment (previously observed by increasing the stimulus voltage). How are they similar? How was each achieved in the experiment? Explain how each is achieved in vivo . Your answer: They are similar and achieved the same way, they both rely on increased frequency to the stimuli for both of them to be reached.