Background: fatigue has long been attributed to peripheral mechanism within
the motor units, however, the stimulus for muscular contraction is initiated in the
brain and therefore central fatigue may occur.This study aimed to investigate central
and peripheral contributions to muscle fatigue, immediately and 20 minutes after
physical and electrical fatigue in 25 healthy male volunteers.
Methods: physical fatigue was induced by sustained voluntary contraction of
the first dorsal interossus muscle (FDI) lasted 10 minutes or till fatigue developed.
While electrical fatigue was induced by transcutaneous electrical stimulation with
trains of submaximal, 100-µs pulses at 20 Hz for 3 minutes. Resting motor threshold,
input-out put curve, motor evoked potential, cortical silent period duration,
interference pattern of the right FDI and M/F ratio of ulnar nerve, all were recorded
before, immediately and 20 minutes after test of fatigue.
Results: resting motor threshold, cortical silent period were significantly
increased and input output curve was significantly suppressed immediately after
physical fatigue. The reverse was observed after electrical fatigue. The amplitude of
interference pattern and the envelope were significantly reduced immediately after
physical fatigue. The same results were recorded after electrical fatigue. Almost all
these changes returned nearly to baseline value 20 minutes after fatigue.
Conclusion: Central inhibition was recorded after physical fatigue while some
cortical facilitation was proofed after electrical fatigue. However, peripheral
inhibition was observed after physical and electrical fatigue. These changes return
nearly to the base line 20 minutes after rest.