Neural control of shortening and lengthening contractions: influence of task constraints

Jacques Duchateau; Roger M. Enoka

doi:10.1113/jphysiol.2008.160747

Neural control of shortening and lengthening contractions: influence of task constraints

The Journal of Physiology ◽

10.1113/jphysiol.2008.160747 ◽

2008 ◽

Vol 586 (24) ◽

pp. 5853-5864 ◽

Cited By ~ 98

Author(s):

Jacques Duchateau ◽

Roger M. Enoka

Keyword(s):

Neural Control ◽

Lengthening Contractions ◽

Task Constraints

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Muscle length: A new feature to investigate neural control of lengthening contractions

Experimental Physiology ◽

10.1113/ep088455 ◽

2020 ◽

Vol 105 (6) ◽

pp. 930-931

Author(s):

Marc Jubeau ◽

Valentin Doguet

Keyword(s):

Neural Control ◽

Muscle Length ◽

Lengthening Contractions ◽

New Feature

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Consequences of biomechanically constrained tasks in the design and interpretation of synergy analyses

Journal of Neurophysiology ◽

10.1152/jn.00769.2013 ◽

2015 ◽

Vol 113 (7) ◽

pp. 2102-2113 ◽

Cited By ~ 45

Author(s):

Katherine M. Steele ◽

Matthew C. Tresch ◽

Eric J. Perreault

Keyword(s):

Matrix Factorization ◽

Muscle Activity ◽

Neural Control ◽

Muscle Activation ◽

Neuromuscular Control ◽

Task Constraints ◽

Factorization Algorithms ◽

Low Dimensional ◽

Or Task ◽

And Task

Matrix factorization algorithms are commonly used to analyze muscle activity and provide insight into neuromuscular control. These algorithms identify low-dimensional subspaces, commonly referred to as synergies, which can describe variation in muscle activity during a task. Synergies are often interpreted as reflecting underlying neural control; however, it is unclear how these analyses are influenced by biomechanical and task constraints, which can also lead to low-dimensional patterns of muscle activation. The aim of this study was to evaluate whether commonly used algorithms and experimental methods can accurately identify synergy-based control strategies. This was accomplished by evaluating synergies from five common matrix factorization algorithms using muscle activations calculated from 1) a biomechanically constrained task using a musculoskeletal model and 2) without task constraints using random synergy activations. Algorithm performance was assessed by calculating the similarity between estimated synergies and those imposed during the simulations; similarities ranged from 0 (random chance) to 1 (perfect similarity). Although some of the algorithms could accurately estimate specified synergies without biomechanical or task constraints (similarity >0.7), with these constraints the similarity of estimated synergies decreased significantly (0.3–0.4). The ability of these algorithms to accurately identify synergies was negatively impacted by correlation of synergy activations, which are increased when substantial biomechanical or task constraints are present. Increased variability in synergy activations, which can be captured using robust experimental paradigms that include natural variability in motor activation patterns, improved identification accuracy but did not completely overcome effects of biomechanical and task constraints. These results demonstrate that a biomechanically constrained task can reduce the accuracy of estimated synergies and highlight the importance of using experimental protocols with physiological variability to improve synergy analyses.

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Excitability at the Motoneuron Pool and Motor Cortex Is Specifically Modulated in Lengthening Compared to Isometric Contractions

Journal of Neurophysiology ◽

10.1152/jn.91104.2008 ◽

2009 ◽

Vol 101 (4) ◽

pp. 2030-2040 ◽

Cited By ~ 63

Author(s):

M. Gruber ◽

V. Linnamo ◽

V. Strojnik ◽

T. Rantalainen ◽

J. Avela

Keyword(s):

Motor Cortex ◽

Neural Control ◽

Biceps Brachii ◽

Cortical Excitability ◽

Motor Evoked Potentials ◽

Isometric Contractions ◽

Spinal Level ◽

Lengthening Contractions ◽

Control Of Muscle Contraction ◽

Isometric Muscle

Neural control of muscle contraction seems to be unique during muscle lengthening. The present study aimed to determine the specific sites of modulatory control for lengthening compared with isometric contractions. We used stimulation of the motor cortex and corticospinal tract to observe changes at the spinal and cortical levels. Motor-evoked potentials (MEPs) and cervicomedullary MEPs (CMEPs) were evoked in biceps brachii and brachioradialis during maximal and submaximal lengthening and isometric contractions at the same elbow angle. Sizes of CMEPs and MEPs were lower in lengthening contractions for both muscles (by ∼28 and ∼16%, respectively; P < 0.01), but MEP-to-CMEP ratios increased (by ∼21%; P < 0.05). These results indicate reduced excitability at the spinal level but enhanced motor cortical excitability for lengthening compared with isometric muscle contractions.

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