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Firing pattern of type‐identified wrist extensor motor units during wrist extension and hand clenching in humans
Author(s) -
Sturm Hendrik,
Schmied Annie,
Vedel JeanPierre,
Pagni Simone
Publication year - 1997
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.1997.735bd.x
Subject(s) - coactivation , isometric exercise , wrist , motor unit , electromyography , reciprocal inhibition , medicine , physical medicine and rehabilitation , anatomy , physical therapy , inhibitory postsynaptic potential
1 Single motor unit activity was investigated in the extensor carpi radialis muscles during voluntary isometric contraction involving either the coactivation of the wrist agonist extensor muscles (wrist extension) or the coactivation of the wrist and finger antagonist extensor and flexor muscles (hand clenching). 2 The motor units were found to be activated at a similar level of motoneurone pool drive during both wrist extension and hand clenching, as indicated by the fact that the EMG activity at which they were recruited was practically the same in both cases (mean ± s.d. : 20 ± 26 and 21 ± 25 mV, respectively). In addition, the net excitatory drive exerted on the motoneurones, as assessed from the mean interspike intervals, did not differ significantly between the two tasks (mean ± s.d. : 104.57 ± 17.24 and 103.01 ± 16.26 ms, for wrist extension and hand clenching, respectively). 3 However, the discharge variability, in terms of the coefficient of variation of the interspike intervals, was slightly but significantly greater during hand clenching than during wrist extension (0.213 ± 0.049 and 0.198 ± 0.045, respectively). This increase involved all types of motor units, regardless of their contractile force. 4 We suggest that the greater motoneurone discharge variability observed during hand clenching may be attributable to an increase in the synaptic noise. This increase might be due to the activation of numerous afferent pathways mediating reciprocal interactions between antagonist motoneurone pools, as well as to the activation of hand cutaneous receptors that play a major role in the regulation of handling and gripping motor activities.