Discharge frequency and discharge pattern of human motor units during voluntary contraction of muscle

Person, R. S.; Kudina, Lydia P.

doi:10.1016/0013-4694(72)90058-2

Cited by 374 publications

(220 citation statements)

References 31 publications

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“…Type IIa muscle fibers fire in the range of 20-50 Hz (30), and, albeit small in amplitude relative to the peak signals generated by strenuous activities such as running, these higher-frequency signals are, over time, a predominant component of the mechanical energy in the musculoskeletal system (31). Conditions such as aging reduce these higher-frequency domain signals (32) and suggest that the age- Fig.…”

Section: Discussionmentioning

confidence: 99%

Adipogenesis is inhibited by brief, daily exposure to high-frequency, extremely low-magnitude mechanical signals

Rubin¹,

Capilla²,

Luu³

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

237

198

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Obesity, a global pandemic that debilitates millions of people and burdens society with tens of billions of dollars in health care costs, is deterred by exercise. Although it is presumed that the more strenuous a physical challenge the more effective it will be in the suppression of adiposity, here it is shown that 15 weeks of brief, daily exposure to high-frequency mechanical signals, induced at a magnitude well below that which would arise during walking, inhibited adipogenesis by 27% in C57BL/6J mice. The mechanical signal also reduced key risk factors in the onset of type II diabetes, nonesterified free fatty acid and triglyceride content in the liver, by 43% and 39%, respectively. Over 9 weeks, these same signals suppressed fat production by 22% in the C3H.B6 -6T congenic mouse strain that exhibits accelerated age-related changes in body composition. In an effort to understand the means by which fat production was inhibited, irradiated mice receiving bone marrow transplants from heterozygous GFP ؉ mice revealed that 6 weeks of these low-magnitude mechanical signals reduced the commitment of mesenchymal stem cell differentiation into adipocytes by 19%, indicating that formation of adipose tissue in these models was deterred by a marked reduction in stem cell adipogenesis. Translated to the human, this may represent the basis for the nonpharmacologic prevention of obesity and its sequelae, achieved through developmental, rather than metabolic, pathways. mesenchymal stem cells ͉ obesity ͉ therapeutics ͉ diabetes ͉ vibration

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Section: Discussionmentioning

confidence: 99%

Adipogenesis is inhibited by brief, daily exposure to high-frequency, extremely low-magnitude mechanical signals

Rubin¹,

Capilla²,

Luu³

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

237

198

View full text Add to dashboard Cite

show abstract

“…In general, the lesser EMG during an eccentric contraction when lowering a given load (6,42) is attributed to a lower discharge rate and the recruitment of fewer motor units (6,23,34). The reduction in discharge rate likely includes an increased variability in discharge (12,23,29,30), which can decrease twitch fusion and increase the fluctuations in the forces exerted by individual motor units (12,14). Some evidence indicates that discharge rate variability of the motor units and fluctuations in motor output increase with movement speed for both concentric (40,41) and eccentric contractions (22).…”

Section: Discussionmentioning

confidence: 99%

Fluctuations in acceleration during voluntary contractions lead to greater impairment of movement accuracy in old adults

Christou

Shinohara

Enoka

2003

Journal of Applied Physiology

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Christou, Evangelos A., Minoru Shinohara, and Roger M. Enoka. Fluctuations in acceleration during voluntary contractions lead to greater impairment of movement accuracy in old adults. J Appl Physiol 95: 373-384, 2003. First published March 21, 2003 10.1152/japplphysiol.00060. 2003.-The purpose of the study was to assess the effect of movement velocity on the relation between fluctuations in acceleration and the ability to achieve a target velocity during voluntary contractions performed by young (29.5 Ϯ 4.3 yr) and old (74.9 Ϯ 6.2 yr) adults. Subjects performed concentric and eccentric contractions with the first dorsal interosseus muscle while lifting a submaximal load (15% of maximum) at six movement velocities (0.03-1.16 rad/s). Fluctuations in acceleration, the accuracy of matching the target velocity, and electromyographic (EMG) activity were determined from three trials for each contraction type and movement velocity. The fluctuations in acceleration increased with movement velocity for both concentric and eccentric contractions, but they were greatest during fast eccentric contractions (ϳ135%) when there was stronger modulation of acceleration in the 5-to 10-Hz bandwidth. Nonetheless, EMG amplitude for first dorsal interosseus increased with movement velocity only for concentric and not eccentric contractions. Consistent with the minimum variance theory, movement accuracy was related to the fluctuations in acceleration for both types of contractions in all subjects. For a given level of fluctuations in acceleration, however, old subjects were three times less accurate than young subjects. Although the EMG amplitude at each speed was similar for young and old adults, only the young adults modulated the power in the EMG spectrum with speed. Thus the fluctuations in acceleration during voluntary contractions had a more pronounced effect on movement accuracy for old adults compared with young adults, probably due to factors that influenced the frequency-domain characteristics of the EMG. concentric contraction; eccentric contraction; electromyogram; first dorsal interosseus; frequency spectrum THE FORCE EXERTED BY A MUSCLE during a voluntary contraction is not constant, but rather it fluctuates about an average value (2,15,25,33,36). The neural mechanisms most responsible for the fluctuations in the force exerted by hand muscles appear to be the regularity with which motoneurons discharge action potentials and the common modulation of motor unit discharge in the agonist and antagonist muscles (7,10,13,16,41). Fluctuations in muscle force impose a significant constraint on the ability of the nervous system to control movement by influencing the capacity to exert a desired force and to achieve an intended trajectory (17,18,43).The minimum variance theory postulates that the central nervous system attenuates this constraint during the performance of goal-directed movements by selecting activation strategies that minimize the variance in the trajectory of the movement (18,43). One prediction of this theory is t...

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“…Also, the AHP was reduced in amplitude. The high variance in firing rate during locomotion would be expected with a reduction in AHP (Person and Kudina, 1972;Miles et al, 2005). Another Brownstone et al (1992) finding was that the reduction in AHP amplitude was associated with a change in the f-I relation: either the slope was increased, or more often it became zero.…”

Section: State-dependence Of Motoneuron Properties: Modulation Duringmentioning

confidence: 98%

Beginning at the end: Repetitive firing properties in the final common pathway

Brownstone

2006

Progress in Neurobiology

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Since the early 20th century, it has been recognized that motoneurons must fire repetitive trains of action potentials to produce muscle contraction. In 1932, Sir John Eccles, together with Hebbel Hoff, found that action potential spike trains in motor axons were produced by "rhythmic centres", which were within the motoneurons themselves. Two decades later, Eccles attended a Cold Spring Harbor Symposium in NY, USA entitled "The Neuron". Two of the many notable presentations at this symposium were juxtaposed: one by Eccles from the University of Otago, Dunedin, NZL, and the other by J. Walter Woodbury and Harry Patton from the University of Washington, Seattle, USA. Both presentations included data obtained using sharp microelectrodes to study the intracellularly recorded potentials of cat motoneurons. In this review, I discuss some of the events leading up to and surrounding this jointly accomplished advance and proceed to discussion of subsequent studies over 5+ decades that have made use of intracellular recordings from motoneurons to study their repetitive firing behavior. This begins with early descriptions of primary and secondary range firing, and continues to the discovery of dendritic persistent inward currents and their relation to plateau potentials, synaptic amplification, and motoneuronal firing. Following a brief description of the possible mechanisms underlying spike frequency adaptation, I discuss the modulation of repetitive firing properties during various motor behaviors. It has become increasingly clear that the central nervous system has exquisite control of the repetitive firing of motoneurons. Eccles' work laid the foundation for the present-day study of these processes.

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Discharge frequency and discharge pattern of human motor units during voluntary contraction of muscle

Cited by 374 publications

References 31 publications

Adipogenesis is inhibited by brief, daily exposure to high-frequency, extremely low-magnitude mechanical signals

Adipogenesis is inhibited by brief, daily exposure to high-frequency, extremely low-magnitude mechanical signals

Fluctuations in acceleration during voluntary contractions lead to greater impairment of movement accuracy in old adults

Beginning at the end: Repetitive firing properties in the final common pathway

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