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Question : Explain how increasing stimulus frequency affects the amount of force generated by the gastrocnemius muscle during the stimulus train. When the muscle is stimulated at a frequency high enough to cause fused tetinus (15-30 Hz normally), what is occurring constantly, without interruption?

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Sixta Kovacek
Sixta KovacekLv2
28 Sep 2019

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PROBLEM4. (14 points) You have been asked to evaluate the efficacy of a new drug to prevent the onset of clonus in ankle joints of spinal cord injured (SCI) patients. (Clonus is the clinical term referring to the sustained oscillations occurring in spasticity, which is related to hyperreflexia. A video of clonus can be found at: www.youtube.com/watch?v=liE9IVMYZPU). In laboratory animals, the drug has been shown to reduce the gain of the stretch reflex by a factor of 1.6 (i.e., the original gain is divided by 1.6), but it also has the effect of slowing the conduction velocity of neural action potentials from 40 m/s to 30 m/s. You generate a model of clonus which incorporates muscle, spindle, and neuror properties. Your model without the drug produces the Nyquist plot on following page (arrows indicate increasing frequency). See for example, Hidler JM, Rymer WZ. A simulation study of reflex instability in spasticity: origins of clonus. IEEE Trans Rehabil Eng. 1999 Sep:7(3):327-40. Some other additional information youll need: . The distance from the ankle muscle spindles to the innervating motoneurons is 1 m So the time delay due to the neural transmission is the time it takes for action potentials to travel from the spindles to the motoneurons and back. Assume that when the drug is used, the phase of the loop transfer function is equal to -180° at the frequency of 3 Hz. The Nyquist plot is scaled such that both the x and y axes correspond to a scale of 5 cm per 1 unit on both of the axes. . . a) Do you predict that the drug prevents clonus? Show your work on the Nyquist plot. b) Is clonus in SCI patients more of a potential problem in the wrist or the elbow? Justify your answer.

21. Aerobic training would decrease submaximalheart rate, which is beneficial for aerobic performance because

a. it saves energy used by heart beats.

b. it gives longer time for ventricular filling.

c. a and b.

d. None of above.

22. Aerobic training would ________ anaerobicpower during maximal exercise.

a. delay onset of

b. facilitate onset of

c. rely on

23. Compared to untrainedindividuals, trained endurance athletes have

a. higher maximal heartrates.

b. higher resting cardiacoutputs.

c. higher resting heartrates.

d. higher maximal strokevolumes.

24. What is the likely outcome oflow volume, low intensity training?

a. increased aerobiccapacity

b. increased anaerobiccapacity

c. increased aerobic andanaerobic capacity

d. little improvement in eitheraerobic or anaerobic capacity

25. Which of the followingstatements explaining the increase in SV after aerobic training iscorrect?

a. reload, contractility, andafterload increase

b. preload, contractility, andafterload decrease

c. preload and contractilityincrease, afterload decreases

d. preload decreases,contractility and afterload increase


26. When motor units contract moresynchronously,

a. muscles cannot sustainsteady forces anymore

b. muscles increase the rate offorce development

c. the ability to generateforce is impeded

d. a single motor neuron nowinnervates several motor units

27. In general, whole-muscle hypertrophy in humans most likely resultsfrom

a. mostly fiberhyperplasia

b. entirely fiberhyperplasia

c. mostly fiberhypertrophy

d. equal contributions of fiberhypertrophy and fiber hyperplasia

28. Overload can be achieved by

a. increasing intensity.

b. increasing recovery time.

c. a certain type of training.

d. All of above.

29. Resistance training increases forceproduction by

a. neural adaptation followed by intramuscular adaptation.

b. intramuscular adaptation followed by neural adaptation.

c. simultaneous neural and intramuscular adaptation.

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a. increased filling time.

b. increased left ventricular volume.

c. increased cardiac and arterial stiffness.

d. improved intrinsic contractile function.

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d. employ more downhillexercise in the training program

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