Mechanical impedance of the human body in vertical direction

Holmlund, P.; Lundström, Ronnie; Lindberg, Lene

doi:10.1016/s0003-6870(99)00063-0

Cited by 74 publications

(53 citation statements)

References 7 publications

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“…This non-linearity has been observed when sitting with nobackrest (e.g. [3], [8]), when sitting with a reclined backrest [4], when standing [10], and when supine [11]. It has been reported that the influence of vibration magnitude on the resonance frequency is less when sitting in a car driving posture than when sitting with no backrest support [12].…”

Section: Introductionmentioning

confidence: 88%

Apparent mass of the human body in the vertical direction: Inter-subject variability

Toward

Griffin

2011

Journal of Sound and Vibration

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The biodynamic responses of the seated human body to whole-body vibration vary considerably between people, but the reasons for the variability are not well understood. This study was designed to determine how the physical characteristics of people affect their apparent mass and whether inter-subject variability is influenced by the magnitude of vibration and the support of a seat backrest. The vertical apparent masses of 80 seated adults (41 males and 39 females aged 18 to 65) were measured at frequencies between 0.6 and 20 Hz with four backrest conditions (no backrest, upright rigid backrest, reclined rigid backrest, reclined foam backrest) and with three magnitudes of random vibration (0.5, 1.0 and 1.5 ms -2 r.m.s.). Relationships between subject physical characteristics (age, gender, weight, and anthropometry) and subject apparent mass were investigated with multiple regression models. The strongest predictor of the modulus of the vertical apparent mass at 0.6 Hz, at resonance, and at 12 Hz was bodyweight, with other factors having only a marginal effect. After correction for other variables, the principal resonance frequency was most consistently associated with age and body mass index. As age increased from 18 to 65 years, the resonance frequency increased by up to 1.7Hz, and when the body mass index was increased from 18 to 34 kgm -2 the resonance frequency decreased by up to 1.7 Hz. These changes were greater than the 0.9-Hz increase in resonance frequency between sitting without a backrest and sitting with a reclined rigid backrest, and greater than the 1.0-Hz reduction in resonance frequency when the magnitude of vibration increased from 0.5 to 1.5 ms -2 r.m.s. It is concluded that the effects of age, body mass index, posture, vibration magnitude, and weight should be taken into account when defining the vertical apparent mass of the seated human body.

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Section: Introductionmentioning

confidence: 88%

Apparent mass of the human body in the vertical direction: Inter-subject variability

Toward

Griffin

2011

Journal of Sound and Vibration

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“…This non-linearity has been observed with no backrest (e.g. [5,9]), with an upright backrest [10], and when sitting with a reclined backrest [8]. The dynamic properties of seat foam have also been shown to be non-linear, with the stiffness and damping decreasing with increases in the vibration magnitude [11,12].…”

Section: Introductionmentioning

confidence: 95%

The transmission of vertical vibration through seats: Influence of the characteristics of the human body

Toward

Griffin

2011

Journal of Sound and Vibration

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The transmission of vibration through a seat depends on the impedance of the seat and the apparent mass of the seat occupant. This study was designed to determine how factors affecting the apparent mass of the body (age, gender, physical characteristics, backrest contact, and magnitude of vibration) affect seat transmissibility. The transmission of vertical vibration through a car seat was measured with 80 adults (41 males and 39 females aged 18 to 65) at frequencies between 0.6 and 20 Hz with two backrest conditions (no backrest and backrest), and with three magnitudes of random vibration (0.5, 1.0, and 1.5 ms -2 r.m.s.). Linear regression models were used to study the effects of subject physical characteristics (age, gender, and anthropometry) and features of their apparent mass (resonance frequency, apparent mass at resonance and at 12 Hz) on the measured seat transmissibility. The strongest predictor of both the frequency of the principal resonance in seat transmissibility and the seat transmissibility at resonance was subject age, with other factors having only marginal effects. The transmissibility of the seat at 12 Hz depended on subject age, body mass index, and gender. Although subject weight was strongly associated with apparent mass, weight was not strongly associated with seat transmissibility. The resonance frequency of the seat decreased with increases in the magnitude of the vibration excitation and increased when subjects made contact with the backrest. Inter-subject variability in the resonance frequency and transmissibility at resonance was less with greater vibration excitation, but was largely unaffected by backrest contact. A lumped parameter seat-person model showed that changes in seat transmissibility with age can be predicted from changes in apparent mass with age, and that the dynamic stiffness of the seat appeared to increase with increased loading so as to compensate for increases in subject apparent mass associated with increased sitting weight.Author Keywords: seat transmissibility; biodynamics; seats; whole-body vibration; inter-subject variability; posture; age; weight; gender Published as: The transmission of vertical vibration through seats: influence of the characteristics of the human body. Toward, M. G. R. & Griffin, M. J. 19 Dec 2011 In : Journal of Sound and Vibration. 330, 26, p. 6526-6543. 3 Highlights > Transmissibility of a car seat measured with 80 subjects (of both genders, aged 18 to 65 years), with and without backrest. > Subject age was the strongest predictor of seat transmissibility -increased age was associated with increased resonance frequency and increased seat transmissibility at resonance. > Subject weight was not strongly associated with seat transmissibility. > Seat resonance frequency decreased with increased vibration magnitude and increased when using the backrest.

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“…One method of normalisation is to select the lowest frequency where data show high coherence, and to divide the mechanical impedance at all frequencies by the data at the selected frequency, resulting in a dimensionless quantity. For example, Holmlund et al 17) normalise data at 2 Hz, such that all mechanical impedance data equal 1.0 at 2 Hz. For a rigid mass, the normalised mechanical impedance is a straight line with a gradient that depends on the frequency of normalisation (Fig.…”

Section: Normalised Mechanical Impedancementioning

confidence: 99%

Impedance Methods (Apparent Mass, Driving Point Mechanical Impedance and Absorbed Power) for Assessment of the Biomechanical Response of the Seated Person to Whole-body Vibration

Mansfield

2005

Ind Health

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Exposure to whole-body vibration is a risk factor for the development of low back pain. In order to develop a fuller understanding of the response of the seated person to vibration, experiments have been conducted in the laboratory investigating the biomechanics of the seated person. Some of these methods are based on the driving force and acceleration at the seat and are reported in the literature as apparent mass, driving point mechanical impedance or absorbed power. This paper introduces the background behind such impedance methods, the theory and application of the methods. It presents example data showing typical responses of the seated human to wholebody vibration in the vertical, fore-and-aft and lateral directions. It also highlights problems that researchers might encounter in performing, analysing and interpreting human impedance data.

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Mechanical impedance of the human body in vertical direction

Cited by 74 publications

References 7 publications

Apparent mass of the human body in the vertical direction: Inter-subject variability

Apparent mass of the human body in the vertical direction: Inter-subject variability

The transmission of vertical vibration through seats: Influence of the characteristics of the human body

Impedance Methods (Apparent Mass, Driving Point Mechanical Impedance and Absorbed Power) for Assessment of the Biomechanical Response of the Seated Person to Whole-body Vibration

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