EXSC-510: Advanced Exercise Physiology Article Review
Metabolic response of type I and II muscle fibers during repeated bouts of maximal
exercise in humans
Understanding how physiology of the body adapts to exercise can help us
develop more effective exercise programs suitable for our specific needs. Genetics
determines how much of each muscle-fiber type we possess; however, identifying
whether we are fast- or slow-twitch dominant would require an invasive muscle biopsy.
This is the reason why we need to understand the metabolic response to the muscle type
fibers and thus will enables us to identify an exercise program that applies the right
training strategies for the muscle fibers.
The main aim of this study was to identify the deference in utilization of PCr by
the two muscle fiber by measuring the changes in ATP, PCr and Glucose 6-phosphate
after two bout of maximal intensity training so as to relate the changes during exercise
and during recovery. They did find that type II fiber fatigued after the first bout while
type I never changed. Although it was not possible to relate the observed decline in the
rate of type II fiber PCr utilization directly to the loss of muscle force, the decline in force
production during contraction may have been a consequence of the rapid loss of PCr
stores in this fiber type.
This study is of a great significance in that it enables us to understand how
these muscle fibers generate their energy /ATP to power their performance. Also, it
provides explanations of what might cause muscle fatigue during the exercise as well as
identifying which muscle type fiber tend to utilize PCr more. According to the
experiment, muscle type II utilized PCr more than type I which indicated that it is
conditioned for bigger and more powerful forces for shorter durations but fatigue quickly.
We see this as it depleted its PCr quickly as well as failed to replicate its force in the
second bout. Muscle fiber type I on the other hand, had no reduction in force compared to
