Biomedical subjects

J Atha

Publications and source records attributed to J Atha.

At least 19 recordsLinked to original sources

PubMed1994

Reducing the biomechanical stress of lifting by training.

The effectiveness of two methods of training in reducing biomechanical stress during lifting was examined in a sample of 12 men aged 18-40 years. Subjects carried out three 40 min sessions, one session per day, of a simple symmetrical lifting task. No training was given before the first session, which acted as the control condition. before each of the next two sessions training was given in the form of either written guidelines or interactive personal tuition in a crossover design. Interaction of order with method was expected and was of interest. The effectiveness of each training method in relieving the stress of lifting was measured in four ways: by ratings of perceived exertion on the Borg scale; by video analysis of adherence to guideline kinematics; by chronic spinal compression measured by precision stadiometry; and by the relative compression force at L5/S1 calculated using Chaffin's model. Although the differences in the results of the four assessment methods make reservations necessary it is suggested that while brief personal tuition may demonstrably reduce lifting stress even in a simple lifting task, written guidelines for the untrained may be counterproductive and may interfere with habitual skills. It is recommended that the efficiency of lifting training methods be estimated objectively, such as by the methods employed here, before being adopted.

Journal Article↗

PubMed1990

The simulation of aerial movement--IV. A computer simulation model.

A computer simulation model of human airborne movement is described. The body is modelled as 11 rigid linked segments with 17 degrees of freedom which are chosen with a view to modelling twisting somersaults. The accuracy of the model is evaluated by comparing the simulation values of the angles describing somersault, tilt and twist with the corresponding values obtained from film data of nine twisting somersaults. The maximum deviations between simulation and film are found to be 0.04 revolutions for somersault, seven degrees for tilt and 0.12 revolutions for twist. It is shown that anthropometric measurement errors, from which segmental inertia parameters are calculated, have a small effect on a simulation, whereas film digitization errors can account for a substantial part of the deviation between simulation and film values.

Anthropometry↗

PubMed1990

Postural consistency in skilled archers.

The consistency of an archer's postural set at the moment of loose (arrow release) is commonly perceived to be an important determinant of success. The coach seeks, among other things, to provide the archer with information about postural consistency, details of which he acquires by eye or occasionally by video-recordings. The gains that might be achieved from more precise information are examined here. Nine skilled archers, classified into either skilled or elite groups according to their officially computed handicap, were continuously monitored and measured with a three-dimensional co-ordinate analyser (Charnwood Dynamics Coda-3 Scanner) while shooting two ends (series) of three arrows each. Considerable variability was observed in the precision with which the positions of head, elbow and bow at the moment of loose were replicated by archers of similar levels of skill. These results are interpreted to suggest that precise postural consistency may not be the primary feature distinguishing between the performance of archers at the higher skill levels.

Analysis of Variance↗

PubMed1984

Current techniques for measuring motion.

The sports scientist and the ergonomist, although sharing a common disciplinary background, pursue fundamentally different goals. The patterns of approach to the analysis of movement they adopt are, nevertheless, similar and a model of this approach is presented. Some potential sources of error associated with each stage of the process are identified. In measuring motion in sport, cinematography has played a dominant role. The method has obvious advantages; but analysing film is a slow, pedestrian task, and subject to human error. Where an investigator is experienced and understands his problem clearly he can often achieve his aims with a limited number of measurement variables. This may also mean he can adopt automatic and specific techniques of acquiring information. Such methods include alternative photographic techniques, but also involve the specialised transducers and automatic analysers that are now burgeoning in the field. Some of these techniques are discussed.

Journal Article↗

PubMed1982

The spectral characteristics of postural sway behaviour.

To determine whether recognisable profiles of sway behaviour are characteristically found among normal subjects the energy content of a contiguous series of bandwidths were computed from power density spectra of the sway behaviour of 29 young men and 29 young women. No significant differences were observed over time either in the energy content or in the profile shape of the power spectral density (PSD) records when these were subjected to a multivariate profile analysis of variance. It was observed that the majority of energy in the power spectrum, viz. 90% (+/- 4%) in the antero-posterior and 95% (+/- 3%) in the lateral direction, was below 2.0 Hz. Three dominant frequencies of sway were identifiable in 93% of subjects. The modal frequencies in the antero-posterior direction were 0.30-0.45 Hz (primary), 0.60-0.75 Hz (secondary) and 1.05-1.20 Hz (tertiary), and in the lateral direction 0.30-0.45 Hz (primary), 0.45-0.60 Hz (secondary) and 0.75-0.90 Hz (tertiary). These three dominant frequencies were distributed over the full frequency range. An explanation of their origins was not sought but the suggestion is made that they could be driven by common dynamic physiological events. The patterns of energy distribution were simplified and quantified by the calculation of a difference-ratio index. The broad dispersion of the values of this index precludes the suggestion that there could be any clustering of profiles. It is concluded that the frequently postulated clustering of the sway patterns of young adults into recognisable and distinct profiles is without firm foundation. Instead it is suggested that sway behaviour is probably normally and randomly distributed about common respiratory, cardiac and perhaps also other dynamic physiological events.

Energy Metabolism↗

PubMed1982

Three-dimensional ballistocardiographic responses to changes of posture.

In an assessment of cardiovascular performance in eighteen young healthy adults, ballistocardiograms were recorded in three mutually perpendicular directions in both the supine and the seated postures, and in the head-foot direction when standing. From these recordings three-dimensional vector ballistocardiograms were obtained which were found to be consistent over repeated measurements (r = 0.81 to 0.88 for the three components when supine) and sensitive to the functional changes imposed by changes of posture. It was observed that in the antero-posterior ballistocardiogram recorded in the supine position there was, in the IJK complex, an additional peak and trough that was not present in any other directional, or postural, ballistocardiogram. This extra wave is held to reflect the directional change of blood flow in the arch of the aorta due to its sagittal curvature around the trachea and vertebral column. From these three-dimensional recordings the functional mechanical axis of the heart was determined for both the supine and seated positions. although similar these axes were not collinear, there being an 8 degrees greater tilt in both the rightward (29 degrees: 21 degrees) and the posterior (28 degrees: 20 degrees) direction in the seated position.

Adolescent↗

PubMed1981

The role of the antigravity musculature during quiet standing in man.

The view that postural regulation is achieved by controlling the destabilising effects of gravity through myotatic reflex activity was examined using surface electromyography. Forty seconds of recordings were made of myograms from eighteen muscles in each of a sample of nine young adults. It was observed that antigravity muscular activity in standing is generally low and often absent, and that the myograms from the muscles of the right and left sides of the body differed appreciably, the two sides rarely working together. Some sudden and united bursts of antigravity muscle activity could be observed. These might well have been stretch reflex induced, but they were transient and rare. It is concluded that the view that postural control in quiet standing is continuously mediated in a simple way by stretch reflex mechanisms is probably not valid, and that other mechanisms for controlling posture remain to be identified.

Back↗

PubMed1981