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Reports on measurement of muscle fiber conduction velocity in humans are scarce. Inferences on the behavior of conduction velocity have been drawn from the behavior of myoelectric spectral parameters. The present report contains information on conduction velocity and spectral parameters studied at various muscle contraction levels and during and after(More)
This paper addresses the axial stiffness of human lumbar motion segments while subjected to moderate loads. Impacts in axial direction were applied to Functional Spinal Units while they were subjected to weights acting as static pre-load. Accelerations were recorded proximal and distal of the FSU. The transfer function and the resonant frequency were(More)
The disc pressure of the third lumbar disc and the myoelectric activity of several muscles of the back were measured. Three standing and nine unsupported sitting positions were studied as well as eight support parameters and six sedentary tasks. 1. Myoelectric activity is about the same in standing and in relaxed unsupported sitting. In the unsupported(More)
Muscle contractions are modulated by the number of motor units recruited and their respective firing rates. The work described in this report documents an interplay between recruitment and firing rates of motor units. The recruitment of a new motor unit appears to have a disfacilitatory influence on the firing rates of previously activated motor units. It(More)
The myoelectric activity of selected trunk muscles at the L3 level was studied during the development of a controlled isometric axial torque. Muscle activity was recorded with surface electrodes bilaterally over the erector spinae muscles, the rectus abdominus, the obliques externus, and the obliques internus. Subjects applied graded isometric axial torque(More)
The electromyography of the erector spinae muscles was studied in the thoracic and lumbar spines of six male subjects when seated in a forwardly bent position (20°) and whilst carrying extra weight (4 kg) on the front of the chest. The electromyographic responses were compared whilst the volunteers were: (a) seated in this position and exposed to whole body(More)
An impact method, combined with pins placed into the spinous process at L3, has been used to establish the dynamic response of the spine of the seated subject. The resonant frequency is at 4-5 Hz, due primarily to a vertical response of the buttocks-pelvis system. A maximum attenuation at 8 Hz occurs because of a second resonance due to pelvic rotation. The(More)