title: Control of single-joint movements with a reversal.
abstract: We studied the kinematic and electromyographic (EMG) patterns during single-joint elbow flexion movements with a reversal and tested two hypotheses. First, that the amplitude of the second phase of the movement (M(2)) will be controlled by two different means, a drop in the second flexor burst for a small M(2) and an increase in the integral of the extensor burst for larger M(2). Second, based on the muscle stretch-shortening cycle (SSC), that movements reversing without a delay will show a larger extensor burst, as compared to movements that reverse after a delay. Changes in EMG patterns with M(2) amplitude supported the first hypothesis and could be interpreted within the framework of the equilibrium-point hypothesis. The observations also corroborate a hypothesis that discrete movements represent outcomes of an oscillatory control process stopped at a particular phase. In Experiment-2, even the shortest delay at the target led to a significantly larger extensor burst. However, there were no differences in the peak velocity of M2 with and without the delay. These observations do not support a major role of stretch reflexes in the SSC effects during such movements. However, they are compatible with the idea of peripheral factors, such as peripheral muscle and tendon elasticity, playing a major potentiating role in the SSC.
authors.affiliation: Departamento de Fisiologia e Biofísica, Instituto de Biologia, Universidade de Campinas, Campinas, São Paulo, Brazil.
authors.forename: Rodrigo Gaiga
authors.initials: RG
authors.lastname: Paulino
authors.forename: Marcus Vińicius
authors.initials: MV
authors.lastname: Rezende Dos Santos
authors.forename: Mark L
authors.initials: ML
authors.lastname: Latash
authors.forename: Gil Lúcio
authors.initials: GL
authors.lastname: Almeida
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology; D000328:Adult; D001683:Biological Clocks / Q000502:physiology; D004551:Elbow Joint / Q000502:physiology*; D004576:Electromyography / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009068:Movement / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D004856:Postural Balance / Q000502:physiology*; D016059:Range of Motion, Articular / Q000502:physiology*; D012026:Reflex, Stretch / Q000502:physiology