Relationship between electrical and mechanical properties of motor units.

Vogt, Th.; Nix, Wilfred A.; Pfeifer, Bernard A.

doi:10.1136/jnnp.53.4.331

Cited by 29 publications

(21 citation statements)

References 17 publications

(2 reference statements)

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“…In line with most of the previous data obtained on various human muscles (MilnerBrown et al 1973;Milner-Brown and Stein 1975;Stephens and Usherwood 1977;Goldberg and Derfler 1977;Monster and Chan 1977;Vogt et al 1990), the higher the motor unit recruitment threshold, the shorter the twitch rise time, the larger the twitch amplitude and the larger the macro-MUP area turned out to be (Tables 2, 3). The good correlation observed between twitch amplitude and twitch rise time confirms previous data obtained in another extensive study of the same muscle (Schmied et al 1994).…”

Section: Contribution Of the Ia Monosynaptic Inputs To The Motor Unitsupporting

confidence: 89%

The “size principle” and synaptic effectiveness of muscle afferent projections to human extensor carpi radialis motoneurones during wrist extension

Schmied

Morin

et al. 1997

Exp Brain Res

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The question of whether muscle spindle afferents might control human motoneurone activity on the basis of the "size principle" during voluntary contraction was investigated by recording the discharge of single motor units (n = 196) in wrist extensor muscles while stimulating the homonymous muscle spindles by means of tendon taps. The mechanical stimuli were delivered with a constant post-spike delay of 80 ms so that the resulting afferent volleys could be expected to reach the motoneurones towards the end of the inter-spike interval (mean +/- SD duration: 124.7 +/- 11.9 ms). In the six subjects tested, the response probability was found to be significantly correlated with the motor units' functional parameters. Differences in twitch rise times, twitch amplitudes, recruitment thresholds and macro-potential areas were found to account for 18%, 9%, 6% and 2% of the differences in the response probability observed within the whole population of motor units tested. These differences could not be due to differences in firing rate for two reasons: first, the motor units were found to discharge with a similar range of inter-spike intervals whatever their functional characteristics; secondly, the weak positive correlation observed between the response probability and the motor unit firing rate showed parallel regression lines between the late-recruited fast-contracting motor units and the first-recruited slowly contracting motor units, but the y-intercept was significantly higher in the latter case. This confirmed that the responses of the first-recruited slowly contracting motor units tended to be larger whatever the firing rates. In most of the pairs tested in the same experiment, the motor units which had the lowest recruitment thresholds, longest contraction times, smallest contraction forces or smallest motor unit macro-potentials tended to produce the largest responses, which also had the longest latencies. Taking the response latency to be an index of a motoneurone's conduction velocity and therefore of its size, the data obtained with this index and with other functional indices such as the twitch rise times and amplitudes, the macro-potential areas and the recruitment thresholds-can be said to be fully consistent with the "size principle", as previously found in anaesthetized animals. It can be inferred that the presynaptic inhibition which is liable to take action during voluntary contraction does not seem to alter the graded distribution of the muscle afferent projections to human wrist extensor motoneurones.

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Section: Contribution Of the Ia Monosynaptic Inputs To The Motor Unitsupporting

confidence: 89%

The “size principle” and synaptic effectiveness of muscle afferent projections to human extensor carpi radialis motoneurones during wrist extension

Schmied

Morin

et al. 1997

Exp Brain Res

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“…In contrast to our hypothesis of pain-induced inhibition, the number of units recruited during pain was larger compared to baseline, and at a speci®c external force level there was a tendency (P < 0.10) toward a larger amplitude of the concentric MUAPs during pain. These ®ndings could indicate a pain-induced shift toward lower rather than higher MU recruitment levels, since a relationship seems to exist between the MU amplitude obtained from the concentric needle and the size of the MU (Bauermeister and Jabre 1992;Vogt et al 1990). However, this interpretation is not supported since apart from the dierence in number of MUs, only a tendency to a dierence was found in the concentric MUAP apmplitude, and no eect was found on the MUAP area.…”

Section: Discussionmentioning

confidence: 93%

The influence of experimental muscle pain on motor unit activity during low-level contraction

Birch¹,

Christensen²,

Arendt‐Nielsen

et al. 2000

European Journal of Applied Physiology

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In the present study we compared motor unit (MU) activity in a painful extensor carpi ulnaris (ECU) muscle to that of a pain-free control. According to the pain adaptation model the activity of the painful ECU muscle may be inhibited and its antagonist activity increased during wrist extension performed as a pre-defined low-force ramp. The pre-defined low force may then be maintained by increased activity in the pain-free synergist muscles such as the extensor carpi radialis (ECR) muscle. Nine females (31-47 years old) participated in the study. Maximal voluntary contraction (MVC) of the wrist extensors was performed. A catheter was inserted into the ECU muscle to allow the injection of hypertonic saline to evoke muscle pain, and a concentric needle was inserted for the recording of MU activity. Surface electromyograms were recorded from a synergist and an antagonist (ECR and flexor carpi radialis) to the painful ECU muscle. A force ramp of isometric wrist extensions up to 10% MVC, with a force increase of 1% MVC x s(-1), were performed followed by 60 s of sustained contraction at 10% MVC. The number of MUs recruited was almost identical for baseline and with pain, and no effect of experimental muscle pain was found on the properties of the MUs (amplitude, area) or their firing characteristics (mean firing rate, firing variability) during low-force ramp contraction. During the sustained 10% MVC, no effect of pain was found for concentric or surface EMG of the forearm muscles. At low force levels no pain-induced modulations were found in MU activity, when the mechanical condition was similar to that of a control situation.

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“…30 The MacroRep is produced by averaging the macro electromyogram (EMG), triggered by the firing of the SMU. 28 The strong relationship between MacroRep size and the twitch force of SMU in the first dorsal interosseous (FDI) 6,7,34 shows that MacroRep gives a reliable indication of SMU size. Given the shortcomings of other techniques, MacroRep appears to be the procedure of choice for determining SMU size in the jaw muscles.…”

mentioning

confidence: 98%

Recruitment stability in masseter motor units during isometric voluntary contractions

Scutter

Türker

1998

Muscle Nerve

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Relationship between electrical and mechanical properties of motor units.

Cited by 29 publications

References 17 publications

The “size principle” and synaptic effectiveness of muscle afferent projections to human extensor carpi radialis motoneurones during wrist extension

The “size principle” and synaptic effectiveness of muscle afferent projections to human extensor carpi radialis motoneurones during wrist extension

The influence of experimental muscle pain on motor unit activity during low-level contraction

Recruitment stability in masseter motor units during isometric voluntary contractions

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