連続的な筋収縮によって低下する単一運動単位の力閾値

概要

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Preliminary evidence suggests that successive isometric muscle contractions lower the force thresholds (FTs) in single motor units (SMUs). The purpose of the present study was to examine further this observation. FTs of 30 biceps brachii SMUs were recorded from 6 male subjects using fine wire coiled copper electrodes. Subjects rested their upper arm horizontally on a table with their elbow angle set at 90 degrees into flexion. With the forearm in supination, subjects gripped a handle attached t6 a force transducer to generate isometric flexion forces. Visual force feedback was provided by an oscilloscope. The initial mean FT for 30 SMUs was 20.8 N (range 1.8-54.5 N). FTs were found to decline from <10% to 100% over the course of 5 additional successive contractions or more. The initial mean FT was significantly higher (p<0.05) than the mean FT values observed during the final 3 contractions of 5 successive contractions. SMUs exhibiting lower initial FTs generally showed larger percent decreases in FT over successive contractions. Intermittent muscle stretch (90 degrees of extension) reset the SMU FT toward the initial value. This suggests that the source of greater excitatory current in lowering SMU FTs during successive contractions may reside in contraction-induced potentiation of stretch reflex pathways.
早稲田大学の論文
1993-03-25