PMID- 11081826
OWN - NLM
STAT- MEDLINE
DCOM- 20010222
LR  - 20190721
IS  - 0014-4819 (Print)
IS  - 0014-4819 (Linking)
VI  - 134
IP  - 4
DP  - 2000 Oct
TI  - EMG activation patterns during force production in precision grip. III. 
      Synchronisation of single motor units.
PG  - 441-55
AB  - Motor unit (MU) synchronisation during isometric force production in the 
      precision grip was analysed in five subjects performing a visually guided 
      steptracking motor task with three different force levels. With this aim 
      multi-unit electromyographic (EMG) activity of 14 intrinsic and extrinsic finger 
      muscles from 15 experimental sessions was decomposed into the potentials of 
      single MUs. The behaviour of 62 intrinsic and 30 extrinsic MUs in the motor task 
      was quantified. Most MUs displayed a positive correlation between firing rate and 
      grip force. Compared to MUs in extrinsic muscles, intrinsic MUs had steeper 
      regression lines with negative intercepts indicating higher force sensitivity and 
      higher recruitment thresholds. A cross-correlation analysis was performed for 69 
      intra- and 166 intermuscular MU pairs while steady grip force was exerted at the 
      three force levels. Synchronisation, for at least one force level, was found in 
      78% of the intra- and 45% of the intermuscular pairs. The occurrence of 
      synchronisation was not stable over the force range tested. Factors influencing 
      the fluctuations in occurrence and strength of synchronisation were investigated. 
      Force increase was not paralleled by increased synchronisation; in contrast, in 
      most MU pairs, especially intermuscular pairs, synchronisation occurred 
      preferentially at the lower force levels. The recruitment threshold appeared to 
      play a determining role in synchronisation: the more similar the thresholds of 
      two MUs, the greater the probability of them being synchronised at this force 
      level. Synchronised MUs fired on average at a lower frequency than 
      non-synchronised ones. Finally, synchronisation at the multi-unit EMG level does 
      not indicate that all underlying MUs are synchronised, nor does the absence of 
      temporal coupling at the multi-unit level indicate that none of the MUs is 
      synchronised.
FAU - Huesler, E J
AU  - Huesler EJ
AD  - Brain Research Institute, University of Zurich, Switzerland.
FAU - Maier, M A
AU  - Maier MA
FAU - Hepp-Reymond, M C
AU  - Hepp-Reymond MC
LA  - eng
PT  - Journal Article
PT  - Research Support, Non-U.S. Gov't
PL  - Germany
TA  - Exp Brain Res
JT  - Experimental brain research
JID - 0043312
SB  - IM
MH  - *Electromyography
MH  - Fingers
MH  - Hand Strength/*physiology
MH  - Humans
MH  - Isometric Contraction/*physiology
MH  - Motor Neurons/*physiology
MH  - Muscle, Skeletal/*innervation
EDAT- 2000/11/18 11:00
MHDA- 2001/03/03 10:01
CRDT- 2000/11/18 11:00
PHST- 2000/11/18 11:00 [pubmed]
PHST- 2001/03/03 10:01 [medline]
PHST- 2000/11/18 11:00 [entrez]
AID - 10.1007/s002210000484 [doi]
PST - ppublish
SO  - Exp Brain Res. 2000 Oct;134(4):441-55. doi: 10.1007/s002210000484.