Evaluation of Muscle Function by Means of a Muscle-Specific and a Global Index

Gait analysis applications in clinics are still uncommon, for three main reasons: (1) the considerable time needed to prepare the subject for the examination; (2) the lack of user-independent tools; (3) the large variability of muscle activation patterns observed in healthy and pathological subjects. Numerical indices quantifying the muscle coordination of a subject could enable clinicians to identify patterns that deviate from those of a reference population and to follow the progress of the subject after surgery or completing a rehabilitation program. In this work, we present two user-independent indices. First, a muscle-specific index (MFI) that quantifies the similarity of the activation pattern of a muscle of a specific subject with that of a reference population. Second, a global index (GFI) that provides a score of the overall activation of a muscle set. These two indices were tested on two groups of healthy and pathological children with encouraging results. Hence, the two indices will allow clinicians to assess the muscle activation, identifying muscles showing an abnormal activation pattern, and associate a functional score to every single muscle as well as to the entire muscle set. These opportunities could contribute to facilitating the diffusion of surface EMG analysis in clinics.

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Organizing principles for voluntary movement: extending single-joint rules

Journal of Neurophysiology ◽

10.1152/jn.1995.74.4.1374 ◽

1995 ◽

Vol 74 (4) ◽

pp. 1374-1381 ◽

Cited By ~ 37

Author(s):

G. L. Almeida ◽

D. A. Hong ◽

D. Corcos ◽

G. L. Gottlieb

Keyword(s):

Muscle Activation ◽

Sagittal Plane ◽

Movement Control ◽

General Rule ◽

Dynamic Interactions ◽

Multijoint Movement ◽

Muscle Activation Patterns ◽

Antagonist Muscles ◽

The Subject ◽

Emg Patterns

1. Four subjects performed fast flexions of the elbow or shoulder over three different distances. Elbow flexions were performed both in a horizontal, single-degree-of-freedom manipulandum and in a sagittal plane with the limb unconstrained. Shoulder flexions were only performed in the sagittal plane by the unconstrained limb. We simultaneously recorded kinematic and electromyographic (EMG) patterns at the “focal” joint, that which the subject intentionally flexed, and at the other, “nonfocal” joint that the subject had been instructed to not flex. 2. Comparisons of the elbow EMG patterns across tasks show that agonist and antagonist muscles were similar in pattern but not size, reflecting the net muscle torque patterns. Comparisons at the shoulder also revealed similar EMG patterns across tasks that reflected net muscle torques. 3. Comparisons of EMG patterns across joints show that elbow and shoulder flexors behaved similarly. This was not true of the extensors. The triceps EMG burst was delayed for longer distances but the posterior deltoid had an early, distance-invariant onset. 4. Similarities in EMG reflect torque demands required at the focal joint to produce flexion and at the nonfocal joint to reduce extension induced by dynamic interactions with the focal, flexing joint. These similarities appear despite very different kinematic intentions and outcomes. This argues against a strong role for length-sensitive reflexes in their generation. 5. These results support the hypothesis that movements are controlled by muscle activation patterns that are planned for the expected torque requirements of the task. This general rule is true whether we are performing single-joint or multiple-joint movements, with or without external constraints. The similarities between single-joint and multijoint movement control may be a consequence of ontogenetic development of multijoint movement strategies that prove useful and are therefore also expressed under the constrained conditions of specialized tasks such as those performed in single-joint manipulanda.

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Identifying the Dynamics of Leg Muscle Activation During Human Gait Using Neural Oscillator and Fuzzy Compensator

International Clinical Neuroscience Journal ◽

10.15171/icnj.2018.21 ◽

2018 ◽

Vol 5 (3) ◽

pp. 106-112

Author(s):

Reihaneh Ravari ◽

Hamid Reza Kobravi

Keyword(s):

Activity Pattern ◽

Muscle Activation ◽

Rectus Femoris ◽

Chaotic Oscillator ◽

Activation Pattern ◽

Activation Patterns ◽

Muscle Activation Patterns ◽

Proposed Model ◽

Activation Dynamics ◽

Fuzzy Compensator

Background: The goal of this study is to design a model in order to predict the muscle activation pattern because the muscle activation patterns contain valuable information about the muscle dynamics and movement patterns. Therefore, the goal of the presentation of this neural model is to identify the desired muscle activation patterns by Hopf chaotic oscillator during walking. Since the knee muscles activation has a significant effect on the movement pattern during walking, the main concentration of this study is to identify the knee muscles activation dynamics using a modeling technique. Methods: The electromyography (EMG) recording obtained from 5 healthy subjects that electrodes positioned on the tibialis-anterior (TA) and rectus femoris muscles on every 2 feet. In the proposed model, along with the chaotic oscillator, a fuzzy compensator was designed to face the unmolded dynamics. In fact, on the condition, the observed difference between the desired and actual activation patterns violate some specific quantitative ranges, the fuzzy compensator based on predefined rules modify the activity pattern produced by the Hopf oscillator. Results: Some quantitative measures used to evaluate the results. According to the achieved results, the proposed model could generate the trajectories, dynamics of which are similar to the muscle activation dynamics of the studied muscles. In this model, the generated activity pattern by the proposed model cannot follow the desired activity of the TA muscle as well as rectus femoris muscle. Conclusion: The similarity between the generated activity pattern by the model and the activation dynamics of Rectus- Femoris muscle was more in comparison with the similarity observed between activation pattern of Tibialis- Anterior and the pattern generated by the model. In other words, based on the recorded human data, the activation pattern of the Rectus- Femoris is more similar to a rhythmic pattern.

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Segmental specificity in belly dance mimics primal trunk locomotor patterns

Journal of Neurophysiology ◽

10.1152/jn.00693.2016 ◽

2017 ◽

Vol 117 (3) ◽

pp. 1100-1111 ◽

Cited By ~ 3

Author(s):

Marilee M. Nugent ◽

Theodore E. Milner

Keyword(s):

Muscle Activation ◽

Erector Spinae ◽

Control Mechanisms ◽

Muscle Coordination ◽

Belly Dance ◽

Activation Patterns ◽

Muscle Activation Patterns ◽

Novel Approach ◽

Locomotor Patterns ◽

Coordination Patterns

Belly dance was used to investigate control of rhythmic undulating trunk movements in humans. Activation patterns in lumbar erector spinae muscles were recorded using surface electromyography at four segmental levels spanning T10 to L4. Muscle activation patterns for movement tempos of 2 Hz, 3 Hz, and as fast as possible (up to 6 Hz) were compared to test the hypothesis that frequency modulates muscle timing, causing pattern changes analogous to gait transitions. Groups of trained and untrained female subjects were compared to test the hypothesis that experience modifies muscle coordination patterns and the capacity for selective motion of spinal segments. Three distinct coordination patterns were observed. An ipsilateral simultaneous pattern (S) and a diagonal synergy (D) dominated at lower frequencies. The S pattern was selected most often by novices and resembled the standing wave of activation underlying the alternating lateral trunk bending in salamander trotting. At 2 Hz, most trained subjects selected the D pattern, suggesting a greater capacity for segmental specificity compared with untrained subjects. At 3–4 Hz, there emerged an asynchronous pattern (A) analogous to the rostral-caudal traveling wave in salamander and lamprey swimming. The neural networks and mechanisms identified in primitive vertebrates, such as chains of coupled oscillators and segmental crossed inhibitory connections, could explain the patterns observed in this study in humans. Training allows modification of these patterns, possibly through improved capacity for selectively exciting or inhibiting segmental pattern generators. NEW & NOTEWORTHY Belly dance provides a novel approach for studying spinal cord neural circuits. New evidence suggests that primitive locomotor circuits may be conserved in humans. Erector spinae activation patterns during the hip shimmy at different tempos are similar to those observed in salamander walking and swimming. As movement frequency increases, a sequential pattern similar to lamprey swimming emerges, suggesting that primal involuntary control mechanisms dominate in fast lateral rhythmic spine undulations even in humans.

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The Effect of External Weight Distribution on Muscle Activation Pattern during Obstacle Negotiation for Male Participants

Proceedings of the Human Factors and Ergonomics Society Annual Meeting ◽

10.1177/1071181319631241 ◽

2019 ◽

Vol 63 (1) ◽

pp. 37-41

Author(s):

Guofu Yi ◽

Xinting Wang ◽

Junxia Zhang ◽

Shuai Hao ◽

Boyi Hu

Keyword(s):

Lower Extremity ◽

Load Distribution ◽

Muscle Activation ◽

Age Groups ◽

External Loading ◽

Activation Pattern ◽

Activation Patterns ◽

Muscle Activation Pattern ◽

Muscle Activation Patterns ◽

Lower Extremity Muscle

Effects of different age groups and different external loading distribution on lower extremity muscle activation during obstacle crossing tasks were tested in this study. Four young participants and five healthy senior participants performed different walking tasks at their own speed carrying multiple different weights while their lower extremity muscle activation patterns were recorded and compared. Older adults showed significantly increased muscle activation patterns in obstacle negotiation. Furthermore, participants showed altered lower extremity muscle activation patterns with different load distribution.

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Effects of spinal cord injury-induced changes in muscle activation on foot drag in a computational rat ankle model

Journal of Neurophysiology ◽

10.1152/jn.00507.2014 ◽

2015 ◽

Vol 113 (7) ◽

pp. 2666-2675 ◽

Cited By ~ 1

Author(s):

Brian K. Hillen ◽

Devin L. Jindrich ◽

James J. Abbas ◽

Gary T. Yamaguchi ◽

Ranu Jung

Keyword(s):

Spinal Cord ◽

Spinal Cord Injury ◽

Tibialis Anterior ◽

Muscle Activation ◽

Swing Phase ◽

Physiological Data ◽

Muscle Coordination ◽

Muscle Activation Patterns ◽

Muscle Dynamics ◽

Cord Injury

Spinal cord injury (SCI) can lead to changes in muscle activation patterns and atrophy of affected muscles. Moderate levels of SCI are typically associated with foot drag during the swing phase of locomotion. Foot drag is often used to assess locomotor recovery, but the causes remain unclear. We hypothesized that foot drag results from inappropriate muscle coordination preventing flexion at the stance-to-swing transition. To test this hypothesis and to assess the relative contributions of neural and muscular changes on foot drag, we developed a two-dimensional, one degree of freedom ankle musculoskeletal model with gastrocnemius and tibialis anterior muscles. Anatomical data collected from sham-injured and incomplete SCI (iSCI) female Long-Evans rats as well as physiological data from the literature were used to implement an open-loop muscle dynamics model. Muscle insertion point motion was calculated with imposed ankle trajectories from kinematic analysis of treadmill walking in sham-injured and iSCI animals. Relative gastrocnemius deactivation and tibialis anterior activation onset times were varied within physiologically relevant ranges based on simplified locomotor electromyogram profiles. No-atrophy and moderate muscle atrophy as well as normal and injured muscle activation profiles were also simulated. Positive moments coinciding with the transition from stance to swing phase were defined as foot swing and negative moments as foot drag. Whereas decreases in activation delay caused by delayed gastrocnemius deactivation promote foot drag, all other changes associated with iSCI facilitate foot swing. Our results suggest that even small changes in the ability to precisely deactivate the gastrocnemius could result in foot drag after iSCI.

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Impaired muscle phasing systematically adapts to varied relative angular relationships during locomotion in people poststroke

Journal of Neurophysiology ◽

10.1152/jn.00290.2010 ◽

2011 ◽

Vol 105 (4) ◽

pp. 1660-1670 ◽

Cited By ~ 7

Author(s):

Laila Alibiglou ◽

David A. Brown

Keyword(s):

Muscle Activity ◽

Muscle Activation ◽

Activity Patterns ◽

Spatial Relationship ◽

Rectus Femoris ◽

Vastus Medialis ◽

Muscle Coordination ◽

Muscle Activation Patterns ◽

Relative Contribution ◽

Muscle Phasing

After stroke, hemiparesis will result in impairments to locomotor control. Specifically, muscle coordination deficits, in the form of inappropriately phased muscle-activity patterns, occur in both the paretic and nonparetic limbs. These dysfunctional paretic muscle-coordination patterns can adapt to somatosensory inputs, and also the sensorimotor state of nonparetic limb can influence paretic limb. However, the relative contribution of interlimb pathways for improving paretic muscle-activation patterns in terms of phasing remains unknown. In this study, we investigated whether the paretic muscle-activity phasing can be influenced by the relative angular-spatial relationship of the nonparetic limb by using a split-crank ergometer, where the cranks could be decoupled. Eighteen participants with chronic stroke were asked to pedal bilaterally during each task while surface electromyogram signals were recorded bilaterally from four lower extremity muscles (vastus medialis, rectus femoris, tibialis anterior, and soleus). During each experiment, the relative angular crank positions were manipulated by increasing or decreasing their difference by randomly ordered increments of 30° over the complete cycle [0° (in phase pedaling), 30°, 60°, 90°, 120°, 150°, 180° (standard pedaling), 210°, 240°, 270°, 300°, 330° (out of phase pedaling)]. We found that the paretic and nonparetic muscle phasing in the cycle systematically adapted to varied relative angular relationships, and this systematic relationship was well modeled by a sinusoidal relationship. Also, the paretic uniarticular muscle (vastus medialis) showed larger phase shifts compared with biarticular muscle (rectus femoris). More importantly, for each stroke subject, we demonstrated an exclusive crank-angular relation that resulted in the generation of more appropriately phased paretic muscle activity. These findings provide new evidence to better understand the capability of impaired nervous system to produce a more normalized muscle-phasing pattern poststroke.

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Structured Variability of Muscle Activations Supports the Minimal Intervention Principle of Motor Control

Journal of Neurophysiology ◽

10.1152/jn.90324.2008 ◽

2009 ◽

Vol 102 (1) ◽

pp. 59-68 ◽

Cited By ~ 124

Author(s):

Francisco J. Valero-Cuevas ◽

Madhusudhan Venkadesan ◽

Emanuel Todorov

Keyword(s):

Neural Control ◽

Muscle Activation ◽

Task Demands ◽

Muscle Coordination ◽

Control Effort ◽

Minimal Intervention ◽

Muscle Activation Patterns ◽

Emg Signal ◽

Physiological Evidence ◽

Task Irrelevant

Numerous observations of structured motor variability indicate that the sensorimotor system preferentially controls task-relevant parameters while allowing task-irrelevant ones to fluctuate. Optimality models show that controlling a redundant musculo-skeletal system in this manner meets task demands while minimizing control effort. Although this line of inquiry has been very productive, the data are mostly behavioral with no direct physiological evidence on the level of muscle or neural activity. Furthermore, biomechanical coupling, signal-dependent noise, and alternative causes of trial-to-trial variability confound behavioral studies. Here we address those confounds and present evidence that the nervous system preferentially controls task-relevant parameters on the muscle level. We asked subjects to produce vertical fingertip force vectors of prescribed constant or time-varying magnitudes while maintaining a constant finger posture. We recorded intramuscular electromyograms (EMGs) simultaneously from all seven index finger muscles during this task. The experiment design and selective fine-wire muscle recordings allowed us to account for a median of 91% of the variance of fingertip forces given the EMG signals. By analyzing muscle coordination in the seven-dimensional EMG signal space, we find that variance-per-dimension is consistently smaller in the task-relevant subspace than in the task-irrelevant subspace. This first direct physiological evidence on the muscle level for preferential control of task-relevant parameters strongly suggest the use of a neural control strategy compatible with the principle of minimal intervention. Additionally, variance is nonnegligible in all seven dimensions, which is at odds with the view that muscle activation patterns are composed from a small number of synergies.

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Merging of Healthy Motor Modules Predicts Reduced Locomotor Performance and Muscle Coordination Complexity Post-Stroke

Journal of Neurophysiology ◽

10.1152/jn.00825.2009 ◽

2010 ◽

Vol 103 (2) ◽

pp. 844-857 ◽

Cited By ~ 394

Author(s):

David J. Clark ◽

Lena H. Ting ◽

Felix E. Zajac ◽

Richard R. Neptune ◽

Steven A. Kautz

Keyword(s):

Nervous System ◽

Neural Control ◽

Muscle Activation ◽

Nonnegative Matrix ◽

Modular Organization ◽

Coordination Pattern ◽

Muscle Coordination ◽

Post Stroke ◽

Muscle Activation Patterns ◽

Flexion Extension

Evidence suggests that the nervous system controls motor tasks using a low-dimensional modular organization of muscle activation. However, it is not clear if such an organization applies to coordination of human walking, nor how nervous system injury may alter the organization of motor modules and their biomechanical outputs. We first tested the hypothesis that muscle activation patterns during walking are produced through the variable activation of a small set of motor modules. In 20 healthy control subjects, EMG signals from eight leg muscles were measured across a range of walking speeds. Four motor modules identified through nonnegative matrix factorization were sufficient to account for variability of muscle activation from step to step and across speeds. Next, consistent with the clinical notion of abnormal limb flexion-extension synergies post-stroke, we tested the hypothesis that subjects with post-stroke hemiparesis would have altered motor modules, leading to impaired walking performance. In post-stroke subjects ( n = 55), a less complex coordination pattern was shown. Fewer modules were needed to account for muscle activation during walking at preferred speed compared with controls. Fewer modules resulted from merging of the modules observed in healthy controls, suggesting reduced independence of neural control signals. The number of modules was correlated to preferred walking speed, speed modulation, step length asymmetry, and propulsive asymmetry. Our results suggest a common modular organization of muscle coordination underlying walking in both healthy and post-stroke subjects. Identification of motor modules may lead to new insight into impaired locomotor coordination and the underlying neural systems.

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Muscle Synergies Characterizing Human Postural Responses

Journal of Neurophysiology ◽

10.1152/jn.01360.2006 ◽

2007 ◽

Vol 98 (4) ◽

pp. 2144-2156 ◽

Cited By ~ 298

Author(s):

Gelsy Torres-Oviedo ◽

Lena H. Ting

Keyword(s):

Postural Control ◽

Muscle Activation ◽

Muscle Synergies ◽

Support Surface ◽

Muscle Coordination ◽

Natural Behavior ◽

Activation Patterns ◽

Muscle Activation Patterns ◽

Postural Responses ◽

Automatic Postural Responses

Postural control is a natural behavior that requires the spatial and temporal coordination of multiple muscles. Complex muscle activation patterns characterizing postural responses suggest the need for independent muscle control. However, our previous work shows that postural responses in cats can be robustly reproduced by the activation of a few muscle synergies. We now investigate whether a similar neural strategy is used for human postural control. We hypothesized that a few muscle synergies could account for the intertrial variability in automatic postural responses from different perturbation directions, as well as different postural strategies. Postural responses to multidirectional support-surface translations in 16 muscles of the lower back and leg were analyzed in nine healthy subjects. Six or fewer muscle synergies were required to reproduce the postural responses of each subject. The composition and temporal activation of several muscle synergies identified across all subjects were consistent with the previously identified “ankle” and “hip” strategies in human postural responses. Moreover, intertrial variability in muscle activation patterns was successfully reproduced by modulating the activity of the various muscle synergies. This suggests that trial-to-trial variations in the activation of individual muscles are correlated and, moreover, represent variations in the amplitude of descending neural commands that activate individual muscle synergies. Finally, composition and temporal activation of most of the muscle synergies were similar across subjects. These results suggest that muscle synergies represent a general neural strategy underlying muscle coordination in postural tasks.

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The cost of being stable: Trade-offs between effort and stability across a landscape of redundant motor solutions

10.1101/477083 ◽

2018 ◽

Author(s):

M. Hongchul Sohn ◽

Lena H. Ting

Keyword(s):

Muscle Activity ◽

Muscle Activation ◽

Activation Pattern ◽

Activation Patterns ◽

Trade Off ◽

Muscle Activation Pattern ◽

Muscle Activation Patterns ◽

Limb Dynamics ◽

Trade Offs ◽

Muscular Effort

AbstractCurrent musculoskeletal modeling approaches cannot account for variability in muscle activation patterns seen across individuals, who may differ in motor experience, motor training, or neurological health. While musculoskeletal simulations typically select muscle activation patterns that minimize muscular effort, and generate unstable limb dynamics, a few studies have shown that maximum-effort solutions can improve limb stability. Although humans and animals likely adopt solutions between these two extremes, we lack principled methods to explore how effort and stability shape how muscle activation patterns differ across individuals. Here we characterized trade-offs between muscular effort and limb stability in selecting muscle activation patterns for an isometric force generation task in a musculoskeletal model of the cat hindlimb. We define effort as the sum of squared activation across all muscles, and limb stability by the maximum real part of the eigenvalues of the linearized musculoskeletal system dynamics, with more negative values being more stable. Surprisingly, stability increased rapidly with only small increases in effort from the minimum-effort solution, suggesting that very small amounts of muscle coactivation are beneficial for postural stability. Further, effort beyond 40% of the maximum possible effort did not confer further increases in stability. We also found multiple muscle activation patterns with equivalent effort and stability, which could underlie variability observed across individuals with similar motor ability. Trade-off between muscle effort and limb stability could underlie diversity in muscle activation patterns observed across individuals, disease, learning, and rehabilitation.Author summaryCurrent computational musculoskeletal models select muscle activation patterns that minimize the amount of muscle activity used to generate a movement, creating unstable limb dynamics. However, experimentally, muscle activation patterns with various level of co-activation are observed for performing the same task both within and across individuals that likely help to stabilize the limb. Here we show that a trade-off between muscular effort and limb stability across the wide range of possible muscle activation patterns for a motor task could explain the diversity of muscle activation patterns seen across individuals, disease, learning and rehabilitation. Increased muscle activity is necessary to stabilize the limb, but could also limit the ability to learn new muscle activation pattern, potentially providing a mechanism to explain individual-specific muscle coordination patterns in health and disease. Finally, we provide a straightforward method for improving the physiological relevance of muscle activation pattern and musculoskeletal stability in simulations.

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