Vol. 93, Issue 5, 1744-1752, November 2002
Characteristics of surface mechanomyogram are dependent on
development of fusion of motor units in humans
Yasuhide
Yoshitake1,
Minoru
Shinohara2,
Hidetoshi
Ue1, and
Toshio
Moritani1
1 Laboratory of Applied Physiology, Graduate School
of Human and Environmental Studies, Kyoto University, Sakyo-ku,
Kyoto 606-8501, Japan; and 2 Department of
Kinesiology, The Pennsylvania State University, University Park,
Pennsylvania 16802
The purpose of this study
was to test whether surface mechanomyogram (MMG) recorded on the skin
reflects the contractile properties of individual motor units in
humans. Eight motor units in the medial gastrocnemius muscle were
identified, and trains of stimulation at 5, 10, 15, and 20 Hz were
delivered to each isolated motor unit. There was a significant positive
correlation between the duration of MMG and twitch duration. MMG
amplitude decreased with increasing stimulation frequency. Reductions
in MMG amplitude were in parallel with the reductions in force
fluctuations, and the rate of change in both was positively correlated
across the motor units. Rate of change in MMG amplitude against force
was negatively correlated to half relaxation time and twitch duration. Similar negative correlations were found between force fluctuations and
contractile properties. These results provide evidence supporting a
direct relation between MMG and contractile properties of individual motor units within the gastrocnemius muscle, indicating that surface MMG is dependent on the contractile properties of the activated motor
units in humans.
intramuscular microstimulation; force fluctuation; contractile
property
