Human Physiology with Vernier
17 - 1
LabQuest
17
Grip Strength and Muscle Fatigue
Skeletal muscle is composed of bundles of individual muscle fibers (see Figure 1) and has
unique properties which allow it to respond to stimuli by contracting. Individual muscle fibers
respond to a stimulus (e.g., nerve impulse) with an all or none response, meaning the muscle
fiber contracts to its maximum potential or not at all. Once a muscle has contracted, relaxation
must occur before it can contract again. There are three basic types of muscle fibers:
slow fibers,
fast fibers,
and
intermediate fibers
. Fast fibers contract quickly but for a relatively short
duration. Slow fibers respond less rapidly, but are capable of a more sustained contraction. The
strength of contraction of a whole muscle is dependent on the number of muscle fibers involved.
Muscle fatigue occurs with prolonged or repetitive use of a muscle group, and is familiar to
anyone who has ever carried a heavy suitcase or walked up a long flight of stairs. With fatigue,
there is a sense of weakness and even discomfort, which eventually leads one to discontinue the
activity that is causing it. The mechanism of fatigue is multifactorial and not fully understood,
but is felt to involve the central nervous system, peripheral nervous system, muscle units and
individual muscle fibers. At the level of muscle cells, depletion of energy stores may be
important.
Regular exercise improves muscular function and delays the onset of fatigue, thus increasing the
amount and duration of work that can be performed. Exercise is important for optimal athletic
performance, prevention of injury in athletes and non-athletes, and the maintenance of good
general health.
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