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Biomedical subjects

H Broman

Publications and source records attributed to H Broman.

10 recordsLinked to original sources
PubMed1992

Measurement of height loss during whole body vibrations.

An experimental, in vivo study was performed to measure height changes in subjects exposed to whole body vibrations while seated. Twelve women, with an average age of 22 years, were exposed to sinusoidal vibrations for 5 mins. The vibration frequency was 5 Hz, and the acceleration was 0.1 g Rms. The height loss stemming from vibration exposure was compared with that experienced while sitting without being subjected to vibrations. The height losses that always occurred from the two exposures were corrected for the effect of posture change. The height loss from vibration was significantly greater than when no vibration was present. Height loss due to posture change was responsible for approximately 50% of the total height loss. From this study it was concluded that whole body vibrations cause increased height loss.

Adult↗
PubMed1991

The impact response of the seated subject.

An impact method for establishing the dynamic response of the seated subject is introduced. The method employs a pendulum to apply the impact to the suspended seat. Pins are placed in the spinous process at L3. Highly reproducible results are obtained. The results were not affected by the amplitude of impact, implying a linear system. A marked peak of transmissibility is found in the 4-5 Hz range and an attenuation peak is found close to 8 Hz. Both muscle contraction and postural changes affect the dynamic response. A relaxed posture shows greater gain and attenuation peaks. A valsalva stiffens the system and reduces the effective damping. The vertical response of the body probably shows in the 5-6 Hz peak, while the rotational response is probably encompassed in the 8 Hz attenuation peak.

Adult↗
PubMed1991

Intervertebral motion during vibration.

Vibration exposure is widely recognized as a risk factor for low back pain. An experimental protocol was designed to quantify the intervertebral motion response in human subjects to sinusoidal vertical vibration at 5 and 8 Hz, and at a variety of acceleration levels. Intervertebral motion in the mid-sagittal plane was measured using a transducer linkage system attached to pins placed directly into the spinous processes of adjacent vertebrae. The postures of the subjects were carefully controlled. The effects of forward flexion, arm support, gravitational load, and sitting on a cushion were evaluated. The rigid body motion of the superior vertebra with respect to the inferior vertebra was expressed in terms of relative sagittal plane rotation, axial translation, and anterior-posterior shear translation. It was found that the lumbar motion segments exhibited coupled periodic behaviour in response to sinusoidal vertical vibration, with up to 1 mm peak-to-peak displacement in the axial direction. The greatest intervertebral motion occurred when the subject was exposed to 5 Hz vibration as compared to 8 Hz. For a constant frequency of 5 Hz excitation, the peak-to-peak amplitudes of the computed motions tended to increase as the acceleration level increased. In the flexed posture, with no arm support, the active trunk musculature helped reduce the intervertebral motion. Additional gravitational load on the shoulders caused increased relative axial displacement. A polyethylene foam cushion placed on the seat reduced vibration transmission at 5 Hz excitation and consequently decreased the intervertebral motion.

Adult↗
PubMed1990

Factors affecting the dynamic response of the seated subject.

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 attenuation is also affected by additional load and by the addition of a helmet. Neck braces have no dynamic effect.

Adult↗
PubMed1989

The dynamic response of a subject seated on various cushions.

An impact pendulum was used to examine the dynamic response of the seated subject. The dynamic response is of interest in establishing the relationship between driving and low-back pain. Accelerometers were placed on the seat and in vivo at the L3 vertebra. The transmissibility and phase angle were obtained in the frequency domain for a variety of cushions. Soft cushions were found to increase the gain at the first natural frequency.

Acceleration↗
PubMed1975

The sitting posture: an electromyographic and discometric study.

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 sitting positions the highest level of activity is found in anterior sitting and the lowest in posterior sitting. In the muscles of the cervical and lumbar regions the activity is always lower than in the muscles of the thoracic region. The disc pressure is considerably higher in unsupported sitting than in standing. In the unsupported sitting positions the highest disc pressure is found in anterior sitting and the lowest in sitting straight. 2. Both the myoelectric activity and the disc pressure decrease when the back is supported. Of the support parameters, the backrest inclination is the most important, myoelectric activity and disc pressure both decreasing with an increase in inclination. The disc pressure is considerably reduced also when the lumbar support is increased and when armrests are used. 3. Myoelectric activity and disc pressure are both comparatively low in writing, higher in typing, and still higher in lifting. In the car driver's seat the disc pressure increases both when the gear is shifted and when the clutch pedal is depressed. When the gear is shifted, there is also an increase in myoelectric activity.

Adult↗