Muscular contractions and their effect on the vertical ground reaction force during quiet stance--Part I: Hypothesis and experimental investigation.
There is no consensus as to the origins of the oscillations of the vertical ground reaction force during quiet stance. The concept of a cardiovascular origin is supported by many ballistocardiographic studies, but its exclusivity has never been proven. A new hypothesis was formulated to explain their genesis: there is a neuromuscular postural control system, possibly different from the well-investigated mechanisms controlling the macroscopic sway, responsible for compensating the small endogenous forces perturbing the posture by causing some muscles to contract proportionately to the magnitude of perturbation. These contractions contribute to the ground reaction force oscillations. To verify this hypothesis, a series of experiments simultaneously recording the electrocardiogram, the electromyogram of several muscles, and the ground reaction forces were conducted on ten informed and consenting human subjects. The experimental results confirmed that the hypothesized muscular activity in response to the perturbation induced by the cardiac contraction and subsequent blood movement does in fact exist. The signal detected by electromyography is not a cardioelectric artifact, but an actual myoelectrical activity. Several interesting patterns of muscular activity emerged in this investigation. These results provide the needed background and justification for investigating the use of the vertical ground reaction force, not only in the study of posture, but also in the study of clinical conditions affecting the neuromuscular control and the musculature of the trunk.
Pagnacco
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Mechanical Engineering Department, School of Allied Medical Professions, Ohio State University, Columbus, OH 43210, USA.
Heiss
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Oggero
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D000328:Adult; D001696:Biomechanical Phenomena; D004562:Electrocardiography; D004576:Electromyography; D006801:Humans; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000502:physiology; D009200:Myocardial Contraction; D004856:Postural Balance / Q000502:physiology*; D011187:Posture / Q000502:physiology*; D012815:Signal Processing, Computer-Assisted