Muscle fatigue alters neuromuscular responses. This may lead to increased sensitivity to perturbations and possibly to subsequent injury risk. We studied the effects of muscle fatigue on movement stability during a repetitive upper extremity task. Twenty healthy young subjects performed a repetitive work task, similar to sawing, synchronized with a metronome before and after performing each of ...

When the resistance to a forceful isometric bite is suddenly removed in unloading experiments, the bite force drops to zero and the mandible reaches a constant velocity. This occurs at an initial bite force of 100 N after approximately 12 ms when the incisors have moved 4.5 mm. Reflex activity is far too slow to limit the velocity at impact. To explore the influence of other factors (cocontract...

BACKGROUND Peripheral sensation is the most important sensory system in the maintenance of upright posture in all age groups. With aging, visual and somatosensory processing change their prospective contribution to the maintenance of quiet standing, at debated percentages. Aging is associated with a decrease in balance abilities that, in turn, increases the risk of falling. We used force plate ...

OBJECTIVE This study investigates changes in the neuromuscular activation pattern of the lower limb muscles in stroke survivors when crossing obstacles of three different heights. METHODS Eight stroke survivors and eight age-, height-, and gender-matched healthy controls were recruited and instructed to cross over obstacles with heights of 10, 20, and 30% leg length. Surface electromyography ...

[3] or is moving an exercise machine or an orthotic device. In systems of this nature, the human arm dynamics are integrated with the machine dynamics, resulting in behavior specific to the total system. The performance and stability of the system taken as a whole are both functions of not only the machine dynamics, but also the human arm dynamics. Evideoce for instability in a human-machine sy...

Clinical and experimental results are reviewed concerning muscle weakness in patients with hemiparesis after a stroke. The discussion includes the important role that alterations in the physiology of motor units, notably changes in firing rates and muscle fiber atrophy, play in the manifestation of muscle weakness. This role is compared with the lesser role that spasticity (defined as hyperacti...