Roles of Motor-Unit Recruitment in Producing Force Variability of Simulated Muscle Contractions

Motor Control ◽  
2004 ◽  
Vol 8 (1) ◽  
pp. 64-75 ◽  
Author(s):  
Wan X. Yao
Keyword(s):  
Motor Unit ◽  
Muscle Contractions ◽  
Motor Unit Recruitment ◽  
Force Variability

scholarly journals Motor unit recruitment strategies and muscle properties determine the influence of synaptic noise on force steadiness

2012 ◽  
Vol 107 (12) ◽  
pp. 3357-3369 ◽  
Author(s):  
Jakob L. Dideriksen ◽  
Francesco Negro ◽  
Roger M. Enoka ◽  
Dario Farina
Keyword(s):  
Motor Unit ◽  
Low Frequency ◽  
Spike Trains ◽  
Motor Unit Recruitment ◽  
Force Variability ◽  
Muscle Properties ◽  
Single Motor Unit ◽  
Force Steadiness ◽  
Low Frequency Oscillations ◽  
Synaptic Noise

Motoneurons receive synaptic inputs from tens of thousands of connections that cause membrane potential to fluctuate continuously (synaptic noise), which introduces variability in discharge times of action potentials. We hypothesized that the influence of synaptic noise on force steadiness during voluntary contractions is limited to low muscle forces. The hypothesis was examined with an analytical description of transduction of motor unit spike trains into muscle force, a computational model of motor unit recruitment and rate coding, and experimental analysis of interspike interval variability during steady contractions with the abductor digiti minimi muscle. Simulations varied contraction force, level of synaptic noise, size of motor unit population, recruitment range, twitch contraction times, and level of motor unit short-term synchronization. Consistent with the analytical derivations, simulations and experimental data showed that force variability at target forces above a threshold was primarily due to low-frequency oscillations in neural drive, whereas the influence of synaptic noise was almost completely attenuated by two low-pass filters, one related to convolution of motoneuron spike trains with motor unit twitches (temporal summation) and the other attributable to summation of single motor unit forces (spatial summation). The threshold force above which synaptic noise ceased to influence force steadiness depended on recruitment range, size of motor unit population, and muscle contractile properties. This threshold was low (<10% of maximal force) for typical values of these parameters. Results indicate that motor unit recruitment and muscle properties of a typical muscle are tuned to limit the influence of synaptic noise on force steadiness to low forces and that the inability to produce a constant force during stronger contractions is mainly attributable to the common low-frequency oscillations in motoneuron discharge rates.

scholarly journals Recruitment and derecruitment characteristics of motor units in a hand muscle of young and old adults

2010 ◽  
Vol 108 (6) ◽  
pp. 1659-1667 ◽  
Author(s):  
Mark Jesunathadas ◽  
Adam R. Marmon ◽  
James M. Gibb ◽  
Roger M. Enoka
Keyword(s):  
Motor Unit ◽  
Discharge Rate ◽  
Age Groups ◽  
Motor Units ◽  
Motor Unit Recruitment ◽  
Force Variability ◽  
Old Adults ◽  
Hand Muscle ◽  
The Difference ◽  
Ramp Contractions

The significant decline in motor neuron number after ∼60 yr of age is accompanied by a remodeling of the neuromuscular system so that average motor unit force increases and the ability of old adults to produce an intended force declines. One possible explanation for the loss of movement precision is that the remodeling increases the difference in recruitment forces between successively recruited motor units in old adults and this augments force variability at motor unit recruitment. The purpose of the study was to compare the forces and discharge characteristics of motor units in a hand muscle of young and old adults at motor unit recruitment and derecruitment. The difference in recruitment force between pairs of motor units did not differ between young ( n = 54) and old adults ( n = 56; P = 0.702). However, old adults had a greater proportion of contractions in which motor units discharged action potentials transiently before discharging continuously during the ramp increase in force (young: 0.32; old: 0.41; P = 0.045). Force variability at motor unit recruitment was greater for old adults compared with young adults ( P ≤ 0.010), but discharge rate and discharge variability did not differ between age groups ( P ≥ 0.729). These results suggest that the difference in force between the recruitment of successive motor units does not differ between age groups, but that motor unit recruitment may be more transient and could contribute to the greater variability in force observed in old adults during graded ramp contractions.

Motor-Unit Pool Model of Continuous and Discrete Force Variability

Motor Control ◽  
2011 ◽  
Vol 15 (4) ◽  
pp. 439-455 ◽  
Author(s):  
Xiaogang Hu ◽  
Karl M. Newell
Keyword(s):  
Motor Unit ◽  
Force Variability ◽  
Pool Model

PS-1-4 Quantitative EMG and motor unit recruitment threshold — using concentric needle with quadrifilar electrode —

1995 ◽  
Vol 97 (4) ◽  
pp. S83-S84
Author(s):  
Kazuto Akaboshi ◽  
Masaaki Nagata ◽  
Masaru Sakil ◽  
Yoshihisa Masakado ◽  
Akio Kimura ◽  
...  
Keyword(s):  
Motor Unit ◽  
Motor Unit Recruitment ◽  
Recruitment Threshold ◽  
Quantitative Emg

Determining patterns of motor recruitment during locomotion

2002 ◽  
Vol 205 (3) ◽  
pp. 359-369 ◽  
Author(s):  
James M. Wakeling ◽  
Motoshi Kaya ◽  
Genevieve K. Temple ◽  
Ian A. Johnston ◽  
Walter Herzog
Keyword(s):  
Motor Unit ◽  
Frequency Band ◽  
Fibre Type ◽  
Low Frequency ◽  
Motor Units ◽  
Motor Unit Recruitment ◽  
Medial Gastrocnemius ◽  
Fibre Types ◽  
Myoelectric Signals ◽  
Frequency Bands

SUMMARY Motor units are the functional units of muscle contraction in vertebrates. Each motor unit comprises muscle fibres of a particular fibre type and can be considered as fast or slow depending on its fibre-type composition. Motor units are typically recruited in a set order, from slow to fast, in response to the force requirements from the muscle. The anatomical separation of fast and slow muscle in fish permits direct recordings from these two fibre types. The frequency spectra from different slow and fast myotomal muscles were measured in the rainbow trout Oncorhynchus mykiss. These two muscle fibre types generated distinct low and high myoelectric frequency bands. The cat paw-shake is an activity that recruits mainly fast muscle. This study showed that the myoelectric signal from the medial gastrocnemius of the cat was concentrated in a high frequency band during paw-shake behaviour. During slow walking, the slow motor units of the medial gastrocnemius are also recruited, and this appeared as increased muscle activity within a low frequency band. Therefore, high and low frequency bands could be distinguished in the myoelectric signals from the cat medial gastrocnemius and probably corresponded, respectively, to fast and slow motor unit recruitment. Myoelectric signals are resolved into time/frequency space using wavelets to demonstrate how patterns of motor unit recruitment can be determined for a range of locomotor activities.

The effect of rate of torque development on motor unit recruitment and firing rates during isometric voluntary trapezoidal contractions

2019 ◽  
Vol 237 (10) ◽  
pp. 2653-2664 ◽  
Author(s):  
Jonathan D. Miller ◽  
C. J. Lund ◽  
Marissa D. Gingrich ◽  
Kyle L. Schtul ◽  
Mandy E. Wray ◽  
...  
Keyword(s):  
Motor Unit ◽  
Motor Unit Recruitment ◽  
Firing Rates ◽  
Rate Of Torque Development ◽  
Torque Development
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