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Background: Many factors contribute to control the contractile properties of a muscle. One of these factors is muscle length,
which is inversely related to the relaxation phase of the muscle. When the muscle is lengthened the relaxation phase of the
muscle twitch is prolonged and when muscle is shortened, the relaxation phase is shorter in duration. As a result, a motor unit
discharge varies with the muscle length during voluntary contractions. During electrical stimulations, the order of contraction
of muscle fibers is reversed.
Purpose: In order to determine, if motor neuron discharges accommodates the changes imposed by changing muscle length
during electrically fatiguing protocol and motor unit action potentials were recorded from medial gastrocnemius muscle at
different muscle lengths.
Material & Methods: Sixty healthy male subjects were involved, aged between 18�60 years. They were divided into 2 equal
groups. Subjects in the first group underwent 40 Hz frequency stimulation with the muscle in lengthen position while subjects
in the second group underwent 40 Hz frequency stimulation with the muscle in shortened position. Subjects were required to
tolerate a fatiguing protocol for 20 minutes. The amplitude CMAP were measured pre-test and immediately post-test.
Results: There was significant decrease in the amplitude of CMAP in both groups.
Conclusion: Decline in the amplitude of CMAP do exist between individuals before and after low frequency stimulation
(fatiguing protocol) in both groups, but the decline is more pronounced with the muscle in stretched position.