M-response latencies changes as a tool for studying neuromuscular conduction during cyclic maximal voluntary contractions.
M-response changes during cyclic maximal isometric voluntary forearm flexions were studied using a new method based on the following: 1) Monopolar stimulation of terminal motor point of the brachial biceps muscle by large surface electrodes; 2) Monopolar leading-off by a surface electrode placed on the middle between motor endplates and muscle fibers end; 3) Arm and forearm immobilization; 4) Averaging of M-response triggered by the stimulus during contraction; and 5) Latencies to the peak of negative (L1) and of final positive phase (L2) and peak-to-peak amplitude (PTPA) were measured, and peak-to-peak time (PTPT), which reflected muscle conduction velocity and leading-off electrode-to-end of fibers distance was calculated. Four cycles of 30-s contraction and 5-min rest were performed. Eight M-responses were evoked with a 1 Hz frequency starting from 5th s of the cycle. No significant changes of PTPA and L1 were found. Nevertheless, L2 significantly decreased in the third cycle by 6.4% and in the fourth-cycle by 7.6% of the first cycle value. PTPT decreased in the fourth cycle reaching 87.6% of the initial value. The advantage of the method and the possible causes of changes were discussed.
Gatev
P
P
Institute of Physiology, Bulgarian Academy of Sciences, Sofia.
Draganova
N
N
Swrakova
L
L
D000328:Adult; D004558:Electric Stimulation; D004576:Electromyography; D005260:Female; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology; D009119:Muscle Contraction / Q000502:physiology*; D009132:Muscles / Q000502:physiology; D009431:Neural Conduction / Q000502:physiology*; D009469:Neuromuscular Junction / Q000502:physiology*