PubMed · 15255534
The development of a three-axis accelerometer that can simultaneously measure acceleration in all three directions is to be utilised in a range of emerging applications.
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Diana Hodgins. 2004. A three-axis accelerometer.. https://pubmed.ncbi.nlm.nih.gov/15255534/
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Sinusoidal translation while rotating at constant angular velocity about a vertical axis (translation while rotating, TWR) produces centripetal and translational accelerations along the direction of translation and an orthogonal Coriolis acceleration due to the translation in the rotating frame. Thus, a Coriolis acceleration is produced along the bitemporal axis when oscillating along the naso-occipital axis, and along the naso-occipital axis when oscillating along the bitemporal axis. Together, these components generate an elliptically rotating acceleration vector that revolves around the head in the direction of rotation at the frequency of oscillation. Here we studied the orienting and compensatory responses of rabbits during TWR. Combinations of centripetal and translational accelerations were held constant at 0.5 g, and oscillation frequencies were varied from 0.01-0.33 Hz. The amplitude of the Coriolis acceleration increased with the frequency of translation. Naso-occipital translation caused vergence and pitch at all frequencies and roll at higher frequencies, and bitemporal translation produced roll at all frequencies and vergence and pitch at higher frequencies. The sensitivity of each ocular orienting component to linear acceleration was comparable across the different oscillation frequencies. TWR also induced continuous yaw nystagmus with slow phase velocity in the direction of rotation of the acceleration vector. Thresholds for appearance of nystagmus were 0.05 Hz, corresponding to a Coriolis acceleration of 0.06 g. Mean slow phase velocity for a rotating linear acceleration vector produced by 0.5 g along the translation axis and 0.34 g of Coriolis acceleration along the orthogonal axis were approximately 9 degrees /s. Eye velocities during TWR were similar to those generated by off-vertical axis rotation (OVAR), but were opposite in direction with regard to head rotation, following the direction of the rotating acceleration vector in both paradigms. Both are produced by activation of velocity storage in the vestibular system. One important difference between TWR and OVAR is that the head is always upright with regard to gravity during TWR. We speculate that the brain may use these low amplitude rotating linear accelerations to generate eye velocities that help to orient gaze when making turns during normal locomotion.
We analyzed predictive and reactive grip force behavior in 15 patients with Gilles de la Tourette syndrome (GTS) and 15 sex- and age-matched healthy control subjects. Nine patients were without medication; six patients were on medication. In a first experiment, participants lifted and held instrumented objects of different weight. In a second experiment, participants performed vertical point-to-point and continuous arm movements at different frequencies with a hand-held object. In a third experiment, preparatory and reactive grip force responses to sudden load perturbations were analyzed when a weight was dropped into a hand-held cup either by the subject or unexpectedly by the experimenter. Compared to the healthy subjects, GTS patients had increased grip forces relative to the load force in all tasks. Despite this finding, they adjusted the grip force to changes in load force (due to either a change in the mass lifted or accelerating the mass during continuous movements) in the same way as healthy subjects. The temporal coupling between grip and load force profiles was also similar in patients and healthy controls, and they displayed normal anticipation of impact forces when they dropped a weight into a hand-held cup. We found no significant effect of medication on the performance of GTS patients, regardless of the task performed. These results are consistent with deficient sensory-motor processing in Gilles de la Tourette syndrome.
To identify the underlying physiological mechanisms for the difference in the time to failure for two types of fatiguing contractions, 20 subjects performed force and position tasks with the elbow flexor muscles at a comparable net muscle torque for a similar duration. Prior to terminating each task, blood flow was occluded to estimate the relative amount of feedback transmitted by small-diameter afferents to the spinal cord. Mean arterial pressure at the conclusion of the fatiguing contraction increased similarly for the two tasks (force: 119% +/- 14%; position: 114% +/- 15%). However, the final values for the electromyographic activity for the elbow flexor muscles (26% +/- 14% and 21% +/- 11%, respectively; P < 0.05), and the increase in the fluctuations in acceleration and force (225% +/- 152% and 154% +/- 53%, respectively; P < 0.05) in the sagittal plane, were significantly greater during the position task compared with the force task. These results suggest a different balance in the excitatory and inhibitory inputs to the spinal motor neurons for the two tasks, which has implications for the design of work tasks and exercise prescription in rehabilitation.