Unit 2 Objectives

Exam 2 – Muscle structure/function; fatigue; muscle damage/repair

1.   Discuss how muscle architecture affects muscle force output, shortening velocity, and distance.  Provide a general description as to the types and primary functions of muscles that are arranged in parallel and in pennation.

2.   Describe the sequence of events during an action potential.

3.   Describe the sequence of events at the neuromuscular junction upon receiving an action potential.

4.   Describe the myosin filament of a skeletal muscle fiber.  Include a detailed description and function of the myosin head.

5.   Describe the thin filament of a skeletal muscle fiber.

6.   Describe the cytoskeleton proteins and their functions in the sarcomere.

7.   Describe the sarcoplasmic reticulum and its role in excitation-contraction.

8.   Discuss the signaling process of the T-tubules that leads to Ca2+ release by the sarcoplasmic reticulum. 

9.   Describe ATP hydrolysis by the myosin filament.  Include discussion of the strong- and weak-binding phases.

10.  Discuss factors that affect the rate of ATP hydrolysis by the myosin head as well as factors that affect tension development.

11.  Describe the force-velocity and length-tension relationships in skeletal muscle.  Provide a physiological explanation for these relationships.

12.  Discuss the effect of series elasticity on force output of an intact muscle.  Describe the effect of a rapid quick-stretch on muscle force output and provide a viable explanation for the effect.

13.  Contrast the physical, performance, and biochemical differences of the three fiber types; I, IIa, and IIx.

14.  Briefly, describe the function of muscle receptors: muscle spindles and Golgi tendon organs.

15.  Discuss the concept of central fatigue and its theorized mechanism.

16.  Describe biochemical changes observed in muscle during high-intensity exercise.

17.  Discuss potential causes of peripheral fatigue during high-intensity exercise.  Develop and defend your hypotheses on the primary causes of fatigue during various intensities and durations of exercise.

18.  Describe the role of eccentric movements in exercise-induced muscular damage.

19.  Discuss the Popping-Sarcomere Hypothesis (Morgan, 1990) that explains the damage to a sarcomere following eccentric muscle actions.

20.  Discuss the effects of muscle damage on intracellular Ca2+ and how the disruption of Ca2+ homeostasis initiates further muscle damage. 

21.  Describe the steps involved with the acute response phase that follows exercise-induced muscle damage.

22.  Provide a brief explanation for the stiffness and delayed-onset muscular soreness that follows unaccustomed eccentric exercise.

23.  Briefly, describe the process of muscle repair following exercise-induced muscle injury.

24. Briefly, discuss the primarily hormones involved in protein synthesis and degradation as to their actions and effects.

Reading Objectives

Westerblad, H., D.G. Allen, and J. Lännergren.  Muscle fatigue:  lactic acid or inorganic phosphate the major cause?  News Physiol. Sci. 17: 17-21, 2001. [available online: http://physiologyonline.physiology.org/cgi/reprint/17/1/17]

1.   Discuss the purported effects of low pH on muscle function and fatigue.  Explain the viewpoint of Westerblad et al. in that low pH is not a cause of muscular fatigue from high-intensity exercise.

2.   Westerblad et al. proposed that elevated [Pi]i is the primary cause of muscular fatigue during high-intensity exercise.  Explain the mechanisms whereby elevated [Pi]i could decrease force output.  Discuss the rationale for their proposal. 

3.   Discuss your reaction to the proposal by Westerblad et al.

Optional

Proske, U. and T.J. Allen.  Damage to skeletal muscle from eccentric exercise.  Exerc. Sport Sci. Rev. 33(2): 98-104, 2005.

1.   Explain the basis for why eccentric, but not concentric, exercise causes the initial muscle damage.  Include discussion of the influence of the length-tension relationship.

2.   Briefly, describe the proposed secondary cause of muscle damage initiated by eccentric exercise.

3.   There is a temporary increase of passive tension (stiffness) following exercise-induced muscle damage.  Provide an explanation for this occurrence.

4.   Repeated bouts of eccentric exercise tend to decrease the magnitude of exercise-induced muscle damage and DOMS.  Describe the mechanisms that has been proposed to by the authors to explain the repeated bout effect.

Take-home Question for Exam 2 (turn in your response at the time of Exam 2)

Discuss your hypothesis for the physiological mechanism(s) responsible for fatigue during high-intensity exercise. Discuss the strengths and weaknesses of your hypothesis. Provide an explanation for why other mechanisms are not likely responsible for fatigue. Answers should be double-spaced.