SKELETAL MUSCLE FATIGUE: PHYSIOLOGICAL AND BIOCHEMICAL STUDIES (INTRACELLULAR PH, DIAPHRAGM, ACTION POTENTIAL, EXERCISE-TRAINING)
In the context of this dissertation fatigue can be described as a transient decrease in muscle force generating capacity as a result of sufficiently intense or prolonged work. Previous studies of fatigue have typically dealt with limb skeletal muscles. However, the recent observation that the diaphragm muscle can fatigue and lead to respiratory failure in certain individuals has turned attention to this vital skeletal muscle. In this dissertation the diaphragm muscle was utilized as a model to study skeletal muscle physiology and biochemistry during fatiguing work. Initial studies involved a complete physiological and histochemical characterization of the diaphragm. Briefly stated, the diaphragm is heterogeneous in regard to fiber type composition containing 60% fast- and 40% slow twitch muscle fibers. Not surprizingly diaphragmatic contractile properties were determined to be intermediate between those of fast- and slow twitch muscles. To address the question of diaphragm adaptability animals were exercise-trained on a treadmill using a high-intensity running protocol. Following training muscle glycogen content was elevated in the diaphragm. Despite this glycogen supercompensation, the fatiguability of the diaphragm was unchanged post training. During fatigue a high correlation existed between declining force and rising lactate. In order to accurately assess the role of acidosis on contractile function glass microelectrodes were constructed and used to determine pH alterations following fatiguing stimulation. It was demonstrated for the first time in mammalian muscles, using the direct microelectrode technique, that pH declines during intense contractile activity and returns to resting levels in a time course similar to the recovery of peak force. Moreover, it was demonstrated that, in contrast to previous reports, the decline in force during fatigue is not related to perturbation in membrane electrical properties. Finally, it was observed that following high and low frequency stimulation force production recovered faster at low compared to high frequencies. Following stimulation, fusion at low frequencies increased due to fatigue induced prolongation of twitch duration. The net result being a leftward shift in the force-frequency relationship thus augmenting force at low relative to high frequencies.
METZGER, JOSEPH MARK, "SKELETAL MUSCLE FATIGUE: PHYSIOLOGICAL AND BIOCHEMICAL STUDIES (INTRACELLULAR PH, DIAPHRAGM, ACTION POTENTIAL, EXERCISE-TRAINING)" (1985). Dissertations (1962 - 2010) Access via Proquest Digital Dissertations. AAI8604956.