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Biomedical subjects

J A Main

Publications and source records attributed to J A Main.

At least 19 recordsLinked to original sources
PubMed1997

An anthropomorphic hand exoskeleton to prevent astronaut hand fatigue during extravehicular activities.

This correspondence presents a prototype of a powered hand exoskeleton that is designed to fit over the gloved hand of an astronaut and offset the stiffness of the pressurized space suit. This will keep the productive time spent in extravehicular activity from being constrained by hand fatigue. The exoskeleton has a three-finger design, the third and fourth fingers being combined to lighten and simplify the assembly. The motions of the hand are monitored by an array of pressure sensors mounted between the exoskeleton and the hand. Controller commands are determined by a state-of-the-art programmable microcontroller using pressure sensor input. These commands are applied to a PWM driven dc motor array which provides the motive power to move the exoskeleton fingers. The resultant motion of the exoskeleton allows the astronaut to perform both precision grasping tasks with the thumb and forefinger, as well as a power grasp with the entire hand.

Anthropometry↗
PubMed1996

Accuracy of five electronic pedometers for measuring distance walked.

This is a three-part study that examined the accuracy of five brands of electronic pedometers (Freestyle Pacer, Eddie Bauer, L.L. Bean, Yamax, and Accusplit) under a variety of different conditions. In Part I, 20 subjects walked a 4.88-km sidewalk course while wearing two devices of the same brand (on the left and right side of the body) for each of five different trials. There were significant differences among pedometers (P < 0.05), with the Yamax, Pacer, and Accusplit approximating the actual distance more closely than the other models. The Yamax pedometers showed close agreement, but the left and right Pacer pedometers differed significantly (P = 0.0003) and the Accusplit displayed a similar trend (P = 0.0657). In Part II, the effects of walking surface on pedometer accuracy were examined. Ten of the original subjects completed an additional five trials around a 400-m rubberized outdoor track. The devices showed similar values for sidewalk and track surfaces. In Part III, the effects of walking speed on pedometer accuracy were examined. Ten different subjects walked on a treadmill at various speeds (54, 67, 80, 94, and 107 m.min-1). Pedometers that displayed both distance and number of steps were examined. The Yamax was more accurate than the Pacer and Eddie Bauer at slow-to-moderate speeds (P < 0.05), though no significant differences were seen at the fastest speed. While there are variations among brands in terms of accuracy, electronic pedometers may prove useful in recording walking activities in free-living populations.

Adolescent↗
PubMed1995

Highly mobile space suit material optimization.

This paper discusses the factors that control the flexibility of fabric space suit elements by examining a bending model of a pressurized fabric tube. Results from the model are used to evaluate the current direction in highly mobile EVA glove research and suggest that changes are necessary in the suit and glove fabric selection methodology.

Computer Simulation↗
PubMed1993

The health divide.

Explore the source record for details and available documents.

Health Status↗
PubMed1992

Distribution and orientation of bone in the human lumbar vertebral centrum.

This article describes regional variations in cancellous bone morphology within the human lumbar spine of a 60-year-old woman. An automated imaging technique, based upon the method of directed secants, was used to quantify variations in bone porosity and trabecular size, distribution, and orientation within serial transverse histological sections of the L1 and L2 vertebral centrum. Several morphologically distinct levels of organization were observed along the axis of the centrum. The superior and inferior sections of the centrum were made up of an open-celled network of trabeculae, while the translational and middle sections consisted primarily of plate-like trabeculae forming a closed-cell structure. The densest and most oriented bone was found in the superior and inferior sections of the posterior-lateral centrum, whereas least dense and least oriented bone was found in the central third of the anterior centrum. Average trabecular thickness did not vary appreciably from level to level, but varied considerably within a given level, particularly in the inferior sections of the centrum. The number of trabeculae was lowest in the central sections of the centrum, where plate-like trabeculae were most prevalent. The topological architecture of different levels within the centrum exhibited a remarkable degree of organization, which suggests that the spine, like other skeletal structures, has adapted to functional stresses produced during daily activities. Detailed morphological data are tabulated and should be of use to investigators interested in modeling the three-dimensional structural and physical properties of the lumbar spine.

Data Display↗
PubMed1989

Flexible device for vertebral body replacement.

A novel vertebral prosthesis is presented. The prosthesis was developed for surgical procedures requiring the resection of a complete vertebral body and the adjacent intervertebral discs, the design objective being to develop a flexible implant that would be robust enough to withstand the in vivo stress environment of the human spine. In theory, a flexible implant should preserve a more normal range of motion and apply less stress to surrounding tissue than a rigid implant. A prototype implant was constructed so as to combine a rigid stainless steel structure with flexible silicon rubber elements in order to form an implant with static and dynamic mechanical characteristics similar to those of the anterior spinal column. Implant flexibility characteristics were determined from ex vivo stress-strain behaviour during bending and compressive creep testing. Results from the bending tests indicated good agreement for the lateral and sagittal bending characteristics in comparison with in vitro bending tests of human lumbar motion segments. Comparison of the implant compressive creep response with similar in vitro tests on human lumbar intervertebral discs also demonstrated similarities in the time-dependent mechanical parameters.

Elasticity↗