A Method of Measuring Some Kinetic Properties of Voluntary Muscle Activity

The excitability of resting motoneurons increases following spinal cord injury (SCI). The extent to which motoneuron excitability changes during voluntary muscle activity in humans with SCI, however, remains poorly understood. To address this question, we measured F waves by using supramaximal electrical stimulation of the ulnar nerve at the wrist and cervicomedullary motor-evoked potentials (CMEPs) by using high-current electrical stimulation over the cervicomedullary junction in the first dorsal interosseous muscle at rest and during 5 and 30% of maximal voluntary contraction into index finger abduction in individuals with chronic cervical incomplete SCI and aged-matched control participants. We found higher persistence (number of F waves present in each set) and amplitude of F waves at rest in SCI compared with control participants. With increasing levels of voluntary contraction, the amplitude, but not the persistence, of F waves increased in both groups but to a lesser extent in SCI compared with control participants. Similarly, the CMEP amplitude increased in both groups but to a lesser extent in SCI compared with controls. These results were also found at matched absolutely levels of electromyographic activity, suggesting that these changes were not related to decreases in voluntary motor output after SCI. F-wave and CMEP amplitudes were positively correlated across conditions in both groups. These results support the hypothesis that the responsiveness of the motoneuron pool during voluntary activity decreases following SCI, which could alter the generation and strength of voluntary muscle contractions. NEW & NOTEWORTHY How the excitability of motoneurons changes during voluntary muscle activity in humans with spinal cord injury (SCI) remains poorly understood. We found that F-wave and cervicomedullary motor-evoked potential amplitude, outcomes reflecting motoneuronal excitability, increased during voluntary activity compared with rest in SCI participants but to a lesser extent that in controls. These results suggest that the responsiveness of motoneurons during voluntary activity decreases following SCI, which might affect functionally relevant plasticity after the injury.

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Gravitational and dynamic components of muscle torque underlie tonic and phasic muscle activity during goal-directed reaching

10.1101/138263 ◽

2017 ◽

Author(s):

Erienne Olesh ◽

Bradley Pollard ◽

Valeriya Gritsenko

Keyword(s):

Motion Capture ◽

Muscle Activity ◽

Neural Control ◽

Muscle Activation ◽

Kinetic Properties ◽

Motion Capture Data ◽

Active Muscle ◽

Muscle Torque ◽

Dynamic Components ◽

Muscle Torques

AbstractHuman reaching movements require complex muscle activations to produce the forces necessary to move the limb in a controlled manner. How gravity and the complex kinetic properties of the limb contribute to the generation of the muscle activation pattern by the central nervous system (CNS) is a long-standing question in neuroscience. To address this question, muscle activity is often subdivided into static and phasic components. The former is thought to be related to posture maintenance and transitions between postures. The latter represents the remainder of muscle activity and is thought to be related to active movement production and the compensation for the kinetic properties of the limb. In the present study, we directly addressed how this subdivision of muscle activity into static and phasic components is related to the corresponding components of active muscle torques. Eight healthy subjects pointed in virtual reality to visual targets arranged to create a standard center-out reaching task in three dimensions. Muscle activity and motion capture data were synchronously collected during the movements. The motion capture data were used to calculate gravitational and dynamic components of active muscle torques using a dynamic model of the arm with 5 degrees of freedom. Principal Component Analysis (PCA) was then applied to muscle activity and the torque components, separately, to reduce the dimensionality of the data. Muscle activity was also reconstructed from gravitational and dynamic torque components. Results show that the gravitational and dynamic components of muscle torque represent a significant amount of variance in muscle activity. This method could be used to identify static and phasic components of muscle activity using muscle torques. The contribution of both components to the overall muscle activity was largely equal, unlike their relative contribution to active muscle torques, which may reflect a neural control strategy.

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Lack of Organization or Coordination of Voluntary Muscle Activity

Disorders of Movement ◽

10.1007/978-3-662-48468-5_4 ◽

2015 ◽

pp. 155-205

Author(s):

Davide Martino ◽

Alberto J. Espay ◽

Alfonso Fasano ◽

Francesca Morgante

Keyword(s):

Muscle Activity ◽

Voluntary Muscle

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Non-voluntary muscle activity and myofascial pain syndromes

The Neurobiology of Disease ◽

10.1017/cbo9780511570193.018 ◽

1996 ◽

pp. 169-176

Author(s):

R. H. Westgaard

Keyword(s):

Muscle Activity ◽

Myofascial Pain ◽

Myofascial Pain Syndromes ◽

Voluntary Muscle ◽

Pain Syndromes

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Estimation of maximal muscle electromyographic activity from the relationship between muscle activity and voluntary activation

Journal of Applied Physiology ◽

10.1152/japplphysiol.00557.2020 ◽

2021 ◽

Author(s):

Kenzo C. Kishimoto ◽

Martin E. Heroux ◽

Simon C. Gandevia ◽

Jane E. Butler ◽

Joanna Diong

Keyword(s):

Muscle Activity ◽

Muscle Activation ◽

Medial Gastrocnemius ◽

Voluntary Activation ◽

Emg Activity ◽

Active Movement ◽

Electromyographic Activity ◽

Lateral Gastrocnemius ◽

Voluntary Muscle ◽

The Relationship

Maximal muscle activity recorded with surface electromyography (EMG) is an important neurophysiological measure. It is frequently used to normalize EMG activity recorded during passive or active movement. However, the true maximal muscle activity cannot be determined in people with impaired capacity to voluntarily activate their muscles. Here we determined whether maximal muscle activity can be estimated from muscle activity produced during submaximal voluntary activation. Twenty-five able-bodied adults (18 males, mean age 29 years, range 19-64 years) participated in the study. Participants were seated with the knee flexed 90° and the ankle in 5° of dorsiflexion from neutral. Participants performed isometric voluntary ankle plantarflexion contractions at target torques, in random order: 1, 5, 10, 15, 25, 50, 75, 90, 95, 100% of maximal voluntary torque. Ankle torque, muscle activity in soleus, medial and lateral gastrocnemius muscles, and voluntary muscle activation determined using twitch interpolation were recorded. There was a strong loge-linear relationship between measures of muscle activation and muscle activity in all three muscles tested. Linear mixed models were fitted to muscle activation and loge-transformed EMG data. Each 1% increase in muscle activation increased muscle activity by a mean of 0.027 ln(mV) [95% CI 0.025 to 0.029 ln(mV)] in soleus, 0.025 ln(mV) [0.022 to 0.028 ln(mV)] in medial gastrocnemius, and 0.028 ln(mV) [0.026 to 0.030 ln(mV)] in lateral gastrocnemius. The relationship between voluntary muscle activation and muscle activity can be described with simple mathematical functions. In future, it should be possible to normalize recorded muscle activity using these types of functions.

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