Predictive control of muscle fatigue mechanical effects : implications in the investigation of internal models and posture-movement coordination modes

La fatigue musculaire est un phénomène transitoire communément expérimenté dans la vie quotidienne. Principalement associée à un déficit de production de force, elle s’accompagne également d’une augmentation de l’effort mental à fournir pour déployer un niveau de force particulier. L’augmentation du taux de décharge des afférences nociceptives de petit diamètre (groupes III et IV) lors de contractions fatigantes modifie l’expression des commandes motrices – notamment en raison de processus inhibiteurs associés à leur intégration aux niveaux spinal et supraspinal – ce qui affecte finalement la production motrice. C’est la raison pour laquelle une intention motrice similaire avec et sans fatigue se traduira par des formes gestuelles différentes. Une problématique qui n’a jusque-là jamais été abordée dans la littérature concerne la capacité du Système Nerveux Central (SNC) à anticiper les effets de la fatigue musculaire de façon prédictive. Cette capacité prédictive sera étudiée dans ce travail de thèse au moyen de paradigmes expérimentaux faisant intervenir des processus de contrôle prédictifs de la posture, i.e. les Ajustements Posturaux Anticipés (APAs). Du fait que de nombreux travaux montrent que les APAs sont modulés en fonction des caractéristiques mécaniques du mouvement à venir, l’altération des capacités des muscles focaux grâce à des protocoles de fatigue maîtrisés nous a permis d’apprécier la capacité du SNC à en prédire les effets. Nous verrons que cette capacité est condition-dépendante, à savoir qu’elle dépend de la nature des contractions effectuées (volontaires vs. électro-induites) et du niveau de contraintes cognitives et temporelles imposées lors de la préparation du mouvementMuscle fatigue is a transient and commonly experienced phenomenon. It is mainly associated with loss of force and leads to higher effort to produce a particular force level. The increased discharge rate of the nociceptive afferents (group III and IV) during fatiguing contractions alters motor command expression and finally motor production. An issue that has never been addressed in the literature is the Central Nervous System (CNS) capacity to anticipate muscle fatigue effects in a predictive fashion. This predictive capacity will be investigated thanks to experimental paradigms involving postural predictive processes of control, namely Anticipatory Postural Adjustments (APAs). Because numerous works show that APAs are modulated as a function of the mechanical properties of the upcoming movement, the induction of muscle fatigue at the levels of the focal muscles allowed us to appreciate the CNS capacity to predict muscle fatigue effects. We will demonstrate that this capacity is condition-dependent, i.e. it depends on the nature of the fatiguing contractions performed (voluntary vs. electro-induced) and on the level of cognitive and temporal constraints during movement preparatio

Probing the neuromodulatory gain control system in sports and exercise sciences

The monoaminergic bulbospinal pathways from the brainstem are central to motor functions by regulating the gains of spinal motoneurons and represent, in that respect, probably the primary control system for motoneuron excitability. Yet, the efficiency of this system is few, if not never, assessed in the fields of sports and exercise sciences. In this review paper, we propose a methodological approach intended to assess how this neuromodulatory system affects motoneuron excitability. This approach is based on the use of tendon vibration which can, in certain circumstances, induce the generation of the so-called tonic vibration reflex through the stimulation of muscle spindles. Force and EMG responses to tendon vibration are indeed indicative of how this descending system modulates the gain of the ionotropic inputs from Ia afferents and thus of the strength of the monoaminergic drive. After a brief presentation of the neuromodulatory system and of the mechanisms involved in the generation of the tonic vibration reflex, we address some important methodological considerations regarding the use of the TVR to probe this neuromodulatory gain control system. Hopefully, this paper will encourage sports and exercise scientists to investigate this system

Muscle fatigue effects can be anticipated to reproduce a movement kinematics learned without fatigue

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Muscle spindle thixotropy affects force perception through afferent-induced facilitation of the motor pathways as revealed by the Kohnstamm effect

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What if muscle spindles were also involved in the sense of effort?

International audienceEffort perception is widely acknowledged to originate from central processes within the brain, mediated by the integration of an efference copy of motor commands in sensory areas. However, in this topical review, we aim to challenge this perspective by presenting evidence from neural mechanisms and empirical studies that suggest that reafferent signals from muscle spindles also play a significant role in effort perception. It is now imperative for future research (a) to investigate the precise mechanisms underlying the interactions between the efference copy and reafferent spindle signals in the generation of effort perception, and (b) to explore the potentia

The postural control can be optimized by the first movement initiation condition encountered when submitted to muscle fatigue

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Unexperienced mechanical effects of muscular fatigue can be predicted by the Central Nervous System as revealed by anticipatory postural adjustments

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Fatiguing Neuromuscular Electrical Stimulation Decreases the Sense of Effort During Subsequent Voluntary Contractions in Men

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Muscle fatigue as an investigative tool in motor control: A review with new insights on internal models and posture–movement coordination

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The sensory origin of the sense of effort is context-dependent

The origin of the sense of effort has been debated for several decades and there is still no consensus among researchers regarding the underlying neural mechanisms. Some advocate that effort perception mainly arises from an efference copy originating within the brain while others believe that it is predominantly carried by muscle afferent signals. To move the debate forward, we here tested the hypothesis that there is not one but several senses of effort which depend on the way it is evaluated. For this purpose, we used two different psychophysical tests designed to test effort perception in elbow flexors. One was a bilateral isometric force-matching task in which subjects were asked to direct similar amounts of effort toward their two arms, while the other consisted of a unilateral voluntary isometric contraction in which subjects had to rate their perceived effort using a Borg scale. Throughout two distinct experiments, effort perception was evaluated before and following different tendon vibration protocols intended to differentially desensitize muscle spindles and Golgi tendon organs, and to affect the gain between the central effort and muscle contraction intensity. By putting all the results together, we found that spindle afferents played divergent roles across tasks. Namely, while they only acted as modulators of motor pathway excitability during the bilateral task, they clearly intervened as the predominant psychobiological signal of effort perception during the unilateral task. Therefore, the sensory origin of the sense of effort is not central or peripheral. Rather, it is context-dependent