Biomedical subjects

N J Mansfield

Publications and source records attributed to N J Mansfield.

7 recordsLinked to original sources

PubMed2005

Effect of vibration magnitude, vibration spectrum and muscle tension on apparent mass and cross axis transfer functions during whole-body vibration exposure.

Twelve seated male subjects were exposed to 15 vibration conditions to investigate the nature and mechanisms of the non-linearity in biomechanical response. Subjects were exposed to three groups of stimuli: Group A comprised three repeats of random vertical vibration at 0.5, 1.0 and 1.5 ms(-2) r.m.s. with subjects sitting in a relaxed upright posture. Group B used the same vibration stimuli as Group A, but with subjects sitting in a 'tense' posture. Group C used vibration where the vibration spectrum was dominated by either low-frequency motion (2-7 Hz), high-frequency motion (7-20 Hz) or a 1.0 ms(-2) r.m.s. sinusoid at the frequency of the second peak in apparent mass (about 10-14 Hz) added to 0.5 ms(-2) r.m.s. random vibration. In the relaxed posture, frequencies of the primary peak in apparent mass decreased with increased vibration magnitude. In the tense posture, the extent of the non-linearity was reduced. For the low-frequency dominated stimulus, the primary peak frequency was lower than that for the high-frequency dominated stimulus indicating that the frequency of the primary peak in the apparent mass is dominated by the magnitude of the vibration encompassing the peak. Cross-axis transfer functions showed peaks of about 15-20% and 5% of the magnitudes of the peaks in the apparent mass for x- and y-direction transfer functions, respectively, in the relaxed posture. In the tense posture, cross-axis transfer functions reduced in magnitude with increased vibration, likely indicating a reduced fore-aft pitching of the body with increased tension, supporting the hypothesis that pitching contributes to the non-linearity in apparent mass.

Adult↗

PubMed2005

The European vibration directive--how will it affect the dental profession?

On 6 July 2005, the EU Physical Agents (Vibration) Directive (2002) came into force across all member states. This will mean that legally enforceable limits on hand-arm vibration exposures will be introduced and that risk management must be set in place at work. This article briefly describes the content of the Directive, how this will affect the dental profession and what measures will be required to ensure compliance.

Dental Equipment↗

PubMed2001

Symptoms of musculoskeletal disorders in stage rally drivers and co-drivers.

BACKGROUND: During stage rallying, musculoskeletal injuries may be provoked by the high magnitude of vibration and shock to which the driver and co-driver are exposed. Drivers and co-drivers experience similar exposure to whole body mechanical shocks and vibration but different exposure to hand/wrist stressors. OBJECTIVES: To investigate by a questionnaire study the prevalence of symptoms of musculoskeletal injuries after rallying in 13 professional and 105 amateur stage rally competitors. METHODS: The self administered questionnaire investigated whole body and hand/wrist symptoms of musculoskeletal injury. It was loosely based on the Nordic design. RESULTS: 91% of participants who competed or tested for more than 10 days a year (n=90) reported discomfort in at least one body area after rallying. Problems in the lumbar spine (70%), cervical spine (54%), shoulders (47%), and thoracic spine (36%) were the most common. There was a higher prevalence of cervical spine discomfort for co-drivers (62%) than for drivers (46%). Conversely, there was higher prevalence of discomfort in the hands and wrists for drivers (32%) than co-drivers (9%). The prevalence of low back pain in rally participants is higher than that generally reported for workers exposed to whole body vibration. The prevalence of discomfort in the hand and wrist for rally drivers is similar to that previously reported for Formula 1 drivers. CONCLUSIONS: Most stage rally drivers and co-drivers report symptoms of musculoskeletal injury. It is logical to relate the high prevalence of symptoms of injury to the extreme environment of the rally car.

Adult↗

PubMed2000

Difference thresholds for automobile seat vibration.

Reductions in vehicle vibration that may contribute to improvements in overall vehicle ride could individually be too small to be detected by drivers or passengers. This study investigated the 'difference threshold' (the difference in magnitude between two stimuli which is just sufficient for their difference to be detected) required for a change in vehicle ride to be perceived and whether this was consistent with Weber's Law. Ten male and 10 female subjects sat in a car seat and were exposed to four different reproductions of the vertical vibration recorded on the seat of a car. Three of the stimuli had the same waveform recorded while the car traversed a tarmac surface. This waveform was reproduced using three different magnitudes of vibration at the seat: 0.2, 0.4 and 0.8 m s(-2) r.m.s. (Wb weighted). The other stimulus was recorded with the car traversing a 'pavé' surface that gave a different waveform that was reproduced at a magnitude of 0.4 m s(-2) r.m.s. (Wb weighted). There were significant differences in the absolute difference thresholds measured using the same waveform at the three different magnitudes. When the difference thresholds were expressed in relative terms (the proportion by which two stimuli must differ in magnitude to be discriminated), the relative difference thresholds were approximately 13%, and independent of both the vibration magnitude and the vibration waveform. The results are therefore consistent with Weber's Law. No consistent differences were observed between the responses of male and female subjects.

Adult↗

PubMed2000

Non-linearities in apparent mass and transmissibility during exposure to whole-body vertical vibration.

The causes of low back pain associated with prolonged exposure to whole-body vibration are not understood. An understanding of non-linearities in the biomechanical responses is required to identify the mechanisms responsible for the dynamic characteristics of the body, to allow for the non-linearities when predicting the influence of seating dynamics, and to predict the adverse effects caused by various magnitudes of vibration. Twelve subjects were exposed to six magnitudes, 0.25-2.5ms(-2) rms, of vertical random vibration in the frequency range 0.2-20Hz. The apparent masses of the subjects were determined together with transmissibilities measured from the seat to various locations on the body surface: the upper and lower abdominal wall, at L3, over the posterior superior iliac spine and the iliac crest. There were significant reductions in resonance frequencies for both the apparent mass and the transmissibilities to the lower abdomen with increases in vibration magnitude. The apparent mass resonance frequency reduced from 5.4-4. 2Hz as the magnitude of the vibration increased from 0.25-2.5ms(-2) rms. Vertical motion of the lumbar spine and pelvis showed resonances at about 4Hz and between 8 and 10Hz. When exposed to vertical vibration, the human body shows appreciable non-linearities in its biodynamic responses. Biodynamic models should be developed to reflect the non-linearity.

Abdominal Muscles↗

PubMed1999

The apparent mass of the human body exposed to non-orthogonal horizontal vibration.

Apparent masses of 15 male and 15 female subjects have been measured during exposure to various directions of horizontal vibration. Twenty vibration conditions were used in the experiment. In each of five directions (0, 22.5, 45, 67.5 and 90 degrees to the mid-sagittal plane) subjects were exposed to random vibration in the frequency range of 1.5-20 Hz at 0.25, 0.5 and 1.0 m s(-2) r.m.s. The five remaining conditions were selected to give measurements whereby the magnitude of the x-component of the vibration was fixed and the gamma-component changed and vice-versa. Two peaks were observed in the apparent masses. The first peak occurred at about 3 Hz and reduced in frequency with increases in vibration magnitude. The frequency of the first peak also reduced as the direction of vibration changed from 0 to 90 degrees. The magnitude of the peak increased as the vibration magnitude and direction increased. The second peak occurred at about 5 Hz and decreased in both frequency and magnitude with increases in vibration magnitude. There was no change in the frequency of the second peak with vibration direction, although the magnitude of the peak decreased as the angle of vibration to the mid-sagittal plane increased. Increasing the magnitude of the x-component of vibration whilst using a fixed y-component changed the magnitude of the first peak but did not change the frequency of the first or any characteristics of the second peak. In contrast, increasing the y-component of vibration whilst using a fixed x-component changed the frequencies and magnitudes of both peaks. Predictions of the response at 45 degrees by applying the principle of superposition to data measured at 0 and 90 degrees showed that the response of the body with direction was not linear. This implies that the apparent mass in non-orthogonal axes cannot be predicted from the apparent masses measured in orthogonal directions.

Acceleration↗

PubMed1999

Models of the apparent mass of the seated human body exposed to horizontal whole-body vibration.

BACKGROUND: Many environments contain vibration with simultaneous vertical and horizontal components. Mathematical lumped parameter models of the mechanical impedance of the seated human body have previously been defined for exposure to vertical vibration. This paper proposes models for the response of the seated body when exposed to horizontal vibration. METHODS: Four target functions were derived from previously reported measurements of the apparent masses of seated subjects exposed to fore-and-aft and lateral vibration at both 0.5 and 1.0 ms(-2) r.m.s. Parameters were optimized for six different three degree-of-freedom models to fit the modulus of the model responses to the four target functions. RESULTS: The modulus and phase of the apparent masses optimized for all combinations of vibration magnitude and direction were close to the responses previously measured and reported in the literature. Fitted parameters for all models with elements in series showed at least one element with a parameter that tended to zero. CONCLUSIONS: Models with three parallel single degree-of-freedom systems with a rigid support generally gave the closest representation of the apparent mass of the seated body exposed to horizontal vibration. More experimental data on the effect of gender, posture and magnitude of vibration on the apparent masses of seated subjects would be useful to enable these models to be improved.

Adult↗