Backrest Angle Research Articles

Effects of backrest positioning and gear ratio on nondisabled subjects' handcycling sprinting performance and kinematics

Backrest position is a significant parameter in handcycling that one must consider when seeking to optimize the user-to-chair interface. We studied the effects of backrest position on handcycle propulsion kinematics. Ten nondisabled partici pants with no handcycle propulsion experience repeated an 8 s sprint with three backrest positions (backrest angle between 45 degrees and 50 degrees to the horizontal, backrest angle between 65 degrees and 70 degrees to the horizontal, and without backrest) and three gear ratios (GRs) (GR22/21 = low, GR32/21 = medium, and GR44/21 = high). We used three-dimensional movement analysis to calculate the average maximal velocity, cycle frequency, and angle parameters for the arms and trunk. Our results showed statistically higher trunk flexion/extension (p < 0.001) and maximal velocity (p < 0.001) when a backrest was not used. Moreover, these differences were accentuated as the GR increased (GR44/21). Our results suggest that handcycle users with unimpaired upper-body and trunk function can improve handcycling performance by removing the backrest. Nevertheless, future studies on specific groups of subjects with spinal cord injury should be conducted.

The effects of crank adjustments on handbike propulsion: A kinematic model approach

This study aims to realize a kinematic simulation of handcycling propulsion in order to investigate some ergonomic aspects specific to this mode of propulsion. We hypothesize that adjustments concerning crank position could minimize the joint range of upper extremity motions and/or avoid reaching the joint limit, which are considered as risk factors for repetitive strain injuries (RSI). One paraplegic and one able-bodied participants performed a handcycling test at a 70 rpm crank rate. A 3D analysis of upper extremity motion was made using a Vicon system (Vicon 370). From the data obtained, an inverse kinematic model at seven degrees of freedom was realized. Inputs to the model include the length of the user's arm segments, the position of the user's shoulder and the size of crank used. Joint kinematics are outputs from the model. The movement was simulated by moving the crank axis, or modifying the distance between the two cranks (±10 cm). From our results, the initial position (synchronous mode and a backrest angle close to 90°), like the “downward” and the “backward” positions, seems to generate a lower joint range of motion than other position adjustments. We were able to formulate a hypothesis as to an optimal crank adjustment to reduce risk factors for RSI. This study must be considered as a first step and needs further investigations with a larger population by seeking movement invariant in order to generalize our results. Relevance to industry Results from such a model would serve to guide future research and to help establish guidelines in order to reach an optimal arm crank wheelchair position based on user characteristics. The results of this study provide some ergonomic recommendations for handcycle design and in this way contribute to the further development of novel wheelchair design.

Seat adjustment – capacity and repeatability among occupants in a modern car

Families in the Western world have a car and several family members share the same car. In this study, 154 participants have adjusted a driver's seat three times. The primary objective was to study intrapersonal repeatability and intraclass correlation (ICC) on seat; length adjustment, backrest angle, seat front edge and seat rear edge adjustment, related to participant age, sex, stature and weight. Length adjustment has the best intrapersonal repeatability within two repetitions, 49 mm and ICC-value 0.87. Females and younger participants (age <40 years) adjust seats generally more accurately. Females adjust the seat 41 mm more forward, 120 mm compared to men 79 mm counted from 0-starting position. Females sit with more upright seat backrests, 46° compared to 43° for males counted from 0-starting position. Females sit higher than males in both the frontal and rear part of the seat cushion.

Short daytime naps in a car seat to counteract daytime sleepiness: The effect of backrest angle

A short nap of less than 30 min is an effective countermeasure to prevent afternoon sleepiness and resulting sleep-related accidents. This study was designed to confirm the effectiveness of napping on a car seat equivalent, and to compare two different backrest angles that are preferred by drivers. Eleven healthy university students (mean age 21.3 years, SD = 1.7) completed three experimental conditions: no-nap with the backrest positioned at 105°, and two 15-min naps, with the backrest inclined at 130° or 150°. Both naps with a 130° and 150° backrest incline reduced subjective sleepiness, improved task performance and suppressed slow eye movements (indicators of drowsiness) during the vigilance task. Napping with a backrest angle of 150° reduced subjective fatigue and improved reaction time further than that seen for naps at 130°. These results suggest that a short nap of 15 min in a car seat can counteract afternoon sleepiness and improve task performance. These effects are enhanced when the backrest angle is closer to the horizontal position.

Nurses\' accuracy in estimating backrest elevation

Background. The Centers for Disease Control and Prevention (CDC) have recommended that the head of the bed of mechanically ventilated patients be elevated to between 30° and 45° to decrease the risk of ventilatorassociated pneumonia (VAP) Compliance with this recommendation may be affected by nurses\' knowledge of the recommendation and their accuracy in estimating the backrest elevation. Objectives. To determine the difference between nurses\' estimation of backrest angle and the actual measured angle; to determine the relationship between nurses\' demographic characteristics and the accuracy of estimation; to determine nurses\' knowledge of why this recommendation has been made. Methods. A convenience sample of 39 nurses working in the selected ICUs of the study hospital was used. The angles of elevation were preselected in each area. Estimated angles were correlated with measured angles and this was correlated with demographic characteristics. Results. Forty-two per cent of the nurses were accurate in their estimation of bedrest angle (correlation, 0.6232). Demographic characteristics had little effect on accuracy. Conclusion. Nurses could benefit from assistance in accurately estimating backrest elevation angle, as well as from education regarding strategies to decrease the incidence of ventilator-associated pneumonia. Southern African Journal of Critical Care Vol. 23 (1) 2007: pp. 10-14

Subjective assessment of backrest elevation: Magnitude of error

Backrest elevation, defined as the angle of the backrest height above the horizontal position, is a common nursing intervention that is often used by subjective visual estimation in critically ill patients. The aim of the study was to describe the magnitude of error during the subjective assessment of backrest elevation. This prospective study was conducted in a sample of 160 subjects: 97 registered nurses, 48 undergraduate nursing students, and 15 nursing assistants. Data were collected by recording the degrees of backrest elevation identified by the subjects through an individual random presentation of the selected study angles of 20 degrees, 30 degrees, 35 degrees, 40 degrees, and 45 degrees. A measurement instrument was developed for determination of the angles. Of the 800 investigated angles, 14.9% were estimated accurately, 61.6% were overestimated, and 23.5% were underestimated, with an error average of 8 degrees (+/-13.5 degrees). It was determined that the larger the angle estimated, the greater the average error. A statically significant difference (P <or= .001) was found between the actual degree of backrest elevation and the estimated backrest elevation for 20 degrees, 40 degrees, and 45 degrees with the exception of 30 degrees and 35 degrees, which had similar averages of error. Years of critical care experience did not significantly influence the magnitude of error. The results indicate that the subjective assessment of backrest angle may result in errors that may potentially compromise the patient's condition and supports the need for a more objective method for determining backrest angle.

The relationship of seat backrest angle and neck injury in low-velocity rear impacts

Car-rear-impact-induced cervical spine injuries present a serious burden on society and, in response, seats offering enhanced protection have been introduced. Seats are evaluated for neck protection performance but only at one specific backrest angle, whereas in the real world this varies greatly owing to the variation in occupant physique. Changing the backrest angle modifies the seat geometry and thereby the nature of its interaction with the occupant. Low-velocity rear-impact tests on a BioRID II anthropomorphic test dummy (ATD) have shown that changes in backrest angle have a significant proportionate effect on dummy kinematics. A close correlation was found between changes in backrest angle and the responses of neck injury predictors such as lower neck loading and lower neck shear but not for the neck injury criterion NICmax. Torso ramping was evident, however, with negligible effect in low-velocity impacts. The backrest angle ranged from 20° to 30° whereas the BioRID II spine was adapted to a range from 20° to 26.5°. Nevertheless, in general, instrumentation outputs correlated well, indicating that this ATD could be used for evaluating seats over a 20–30° range rather than solely at 25° as required by current approval test specifications.

Sitter-Selected Postures in an Office Chair with Minimal Task Constraints

Studies of office workers' postures indicate that reclined postures are less common than upright or forward-leaning postures. Laboratory studies have shown that back extensor activity and internal pressure in the lumbar intervertebral disks are lower in reclined postures. Given these advantages, why don't workers recline more often? Postural constraints imposed by their work, particularly vision and hand-reach requirements, may preclude more upright postures. In a study at a large office facility, side-view photographs were used to measure the postures that 80 men and women chose when sitting in an office chair without a work task. All sitters chose substantially reclined postures, with backrest angles averaging 25 degrees from vertical. The findings provide evidence that office work should be designed such that workers can sit more frequently with the reclined torso postures that they would choose if they were not working.

SOME ASPECTS OF THE INVESTIGATION OF RANDOM VIBRATION INFLUENCE ON RIDE COMFORT

Contemporary vehicles must satisfy high ride comfort criteria. This paper attempts to develop criteria for ride comfort improvement. The highest loading levels have been found to be in the vertical direction and the lowest in lateral direction in passenger cars and trucks. These results have formed the basis for further laboratory and field investigations. An investigation of the human body behaviour under random vibrations is reported in this paper. The research included two phases; biodynamic research and ride comfort investigation. A group of 30 subjects was tested. The influence of broadband random vibrations on the human body was examined through the seat-to-head transmissibility function (STHT). Initially, vertical and fore and aft vibrations were considered. Multi-directional vibration was also investigated. In the biodynamic research, subjects were exposed to 0·55, 1·75 and 2·25 m/s2 r.m.s. vibration levels in the 0·5– 40 Hz frequency domain. The influence of sitting position on human body behaviour under two axial vibrations was also examined. Data analysis showed that the human body behaviour under two-directional random vibrations could not be approximated by superposition of one-directional random vibrations. Non-linearity of the seated human body in the vertical and fore and aft directions was observed. Seat–backrest angle also influenced STHT. In the second phase of experimental research, a new method for the assessment of the influence of narrowband random vibration on the human body was formulated and tested. It included determination of equivalent comfort curves in the vertical and fore and aft directions under one- and two-directional narrowband random vibrations. Equivalent comfort curves for durations of 2·5, 4 and 8 h were determined.

8A42 起き上がり姿勢と体圧分布

8A42 起き上がり姿勢と体圧分布

Adaptation and sensitivity to postural change in sitting.

We used 3 psychophysics methods to determine perceptible changes in seat height, seat pan angle, and backrest angle using an experimental chair. In the method of adjustment, the chosen chair settings were affected by the initial setting. For example, a high initial setting of the seat height led to a high selected setting and a low setting led to a low value. The difference between settings was referred to as not noticeable difference (NND). The method of limits was used to determine acceptable chair settings using verbal limits such as "too high" and "too low." Using the method of constant stimuli, just noticeable differences (JNDs) were determined for chair height (1.5 cm), seat pan angle (1.2 degrees) and backrest angle (1.7 degrees). The corresponding values for NNDs and verbal limits were about twice as large: chair height (2.5 cm), seat pan angle (4 degrees) and backrest angle (3 degrees). NNDs and verbal limits are unobtrusive measures that are considered more valid than JNDs, which exaggerate the need for adjustability. The results have practical implications for the design of office chairs.

Optimum seat pan and back-rest parameters for a comfortable tractor seat

An experimental set up was fabricated to measure the pressure distribution on the seat pan and back-rest of a tractor seat. Experiments were conducted with four different seat pans having radius of curvatures of 60, 75, 90 and cm, four backrests with radius of curvatures of 30, 60, 90 and cm, and three back-rest inclinations of 0°, 5° and 10° on representative Indian tractor operators. The subjective assessment of perceived comfort at the seat-operator interface was also recorded. Experiments were conducted in a randomized block design and the data obtained were analysed using suitable computer packages. Results indicate that all the parameters, namely seat pan, back-rest profile curvatures and the back-rest angle of inclination, affect the pressure distribution. It is concluded that a seat pan with radius of curvature 75cm, back-rest with radius of curvature 30 cm and back-rest inclination of 10° are the most suitable parameters for Indian tractor operators.

Whole-body vertical biodynamic response characteristics of the seated vehicle driver: Measurement and model development

The vertical driving-point mechanical impedance characteristics applicable to seated vehicle drivers are measured in the 0.625–10 Hz frequency range with excitation amplitudes ranging from 1.0 to 2.0 m s −2 using a whole-body vehicular vibration simulator. The measurements are performed for seated subjects with feet supported and hands held in a driving position. Variations in the seated posture, backrest angle, and nature and amplitude of the vibration excitation are introduced within a prescribed range of likely conditions to illustrate their influence on the driving-point mechanical impedance of seated vehicle drivers. Within the 0.75–10 Hz frequency range and for excitation amplitudes maintained below 4 m s −2, a four-degree-of-freedom linear driver model is proposed for which the parameters are estimated to satisfy both the measured driving-point mechanical impedance and the seat-to-head transmissibility characteristics defined from a synthesis of published data for subjects seated erect without backrest support. The parameter identification technique involves the solution of a multivariable optimization function comprising the sum of squared magnitude and phase errors associated with both the mechanical impedance and seat-to-head transmissibility target values, subject to limit constraints identified from the anthropometric and biomechanical data. The model response, however, is found to provide a closer agreement with the mechanical impedance target values than that with the seat-to-head transmissibility. From the model, the main body resonant frequencies computed on the basis of both biodynamic response functions are found to be within close bounds to that expected for the human body. Relevance to industry The development of an appropriate analytical seated vehicle driver model should provide means of estimating the forces and motions being transmitted within the body under specific vehicular vibration environments. Furthermore, its use in conjunction with a corresponding model for the vehicle seat should allow the prediction of the driver's vibration exposure levels and the seat's ability to attenuate the vibration in particular vehicles.

The effect of backrest angles on discomfort caused by fore-and-aft back vibration.

The effect on discomfort of the frequency and the backrest angle of x-axis (fore-and-aft) vibration of backrest have been studied. The method of adjustment was employed to obtain contours of equivalent comfort for three types of rigid backrests, whose surface were vertical, inclined 20 degrees and 40 degrees from vertical. Eighteen subjects were required to adjust test vibration over the frequency range 2-80 Hz to produce discomfort equivalent to that caused by 10 Hz 0.25 m/s2 r.m.s. sinusoidal reference vibration for each backrest. The direction of vibration was perpendicular to backrest surface. Results shows that the sensitivity at 20 and 40 Hz on inclined backrests is significantly about 1.4 to 1.5 times greater than that on a vertical backrest (p < 0.01) but there is no significant difference between the two contours for inclined backrests. The contour for a 'vertical' backrest obtained in this experiment agrees with the contour calculated from the frequency weighting factors for x-axis back vibration, Wc, in ISO2631-1, but the contours for inclined backrests do not agree with the contour well.

Considerations for linking seatpan and backrest angles

Modern ergonomic chairs typically have several dimensions that can be adjusted independently of one another. Finding a desirable setting for any one dimension can depend on how other dimensions are set, thereby confronting users with a significant control problem. One design strategy for dealing with this problem has been to link changes in seatpan and backrest angles in some ratio, such that a one‐degree change in seatpan angle is associated with a two‐ or three‐degree change in backrest angle. However, there is no evidence to justify the choice of a particular ratio. This article presents data that addresses this issue. Subjects, performing either an entry or verification task, could adjust the chair to any position. Backrest and seatpan angles were plotted over time and analyzed using both graphical and statistical methods. The resulting scatter plots do not support the industry standard, 1:2 or 1:3 ratio, of changes in seatpan to backrest angles. The possibility of a variable linkage is discussed; however, problems associated with such a solution raise the possibility that control issues might be best addressed through training and exploration.

Preferred Settings in Chair Adjustments

Thirty eight subjects participated in a study to evaluate preferred (comfortable) settings of adjustable chairs including seat height, seat pan angle and back rest angle. An instrumented hydraulic chair was used. The chair was set in one of eight possible extreme position, with each chair parameters at either a high or low value. Subjects then adjusted all three parameters. A full factorial experiment with 5 factors was performed: the three adjustability parameters set at either high or low, gender and replication. Three independent variables were used: preferred seat height, back rest angle and seat pan angle. For the three ANOVA's and across two experiments, 33 statistically significant results were obtained. The initial setting of a parameter (high or low) consistently produced a significant effect in the choice of the preferred setting for the same parameter. The findings imply that there is a range of acceptable settings: for seat height about 1 in. and for the back support angle and seat back angle about 4 degrees.

Quantitative Analysis of Involuntary Movements as a Test of Comfort of a Car Seat: A Study of Man-Machine Interface

Using qualitative analysis of involuntaty movements, comfort/discomfort of a car seat, adjusted in done seat positions-based primarily on the backrest angle has been evaluated. The medial position ...

Physiological Responses and Subjective Discomfort of Simulated Whole-Body Vibration from a Mobile Underground Mining Machine

The U.S. Bureau of Mines has developed an in-house facility to evaluate selected effects of whole-body vibration (WBV) levels experienced by underground mobile equipment operators. Vertical vibration data were collected from a coal haulage vehicle via a uniaxial accelerometer attached to the machine frame under the operator's seat. Data were analyzed and processed so a computer-controlled platform could approximate the vibration signals. Eight men (35.5 yr ± 6.5 SD) participated in a pilot study to evaluate the effects of shock and WBV on heart rate (HR), blood pressure (BP), and subjective discomfort. Subjects were exposed to vibration for 30-min periods while seated in a typical seat (backrest angle at 90° or 130°) that was plain steel or modified with 2 in foam padding. Subjects repeated the same protocol on a separate day, without the vibration. Results indicated the vibration significantly increased the HR (p &lt; 0.01), systolic BP, mean BP, the number of times subjects reported discomfort, and overall subjective discomfort rating (p &lt; 0.05). When seated in the steel seat, the overall discomfort rating (p &lt; 0.001) and the number of times discomfort was reported (p &lt; 0.05) increased significantly. Seatback angle had no significant effect on any of the dependent measures.

Electric goniometer for positioning children with cerebral palsy. Suggestion from the field.

The spatial relationship between the angle of inclination of a seating system's backrest from the seat and the hip flexion angle has not been established for children with cerebral palsy. Therefore, the child's hip flexion angle should not be described as the angle between the seat and the backrest unless the relationship between the hip flexion angle and the backrest's angle of inclination is established. The purpose of this article is to describe the components, operation, and uses of an electric goniometer designed to monitor and measure changes in hip flexion angle while positioning children with cerebral palsy. The position of the hip joint during sitting is crucial to the overall effectiveness of the seating system for children with cerebral palsy. Clinical observations1,2 and research results3 suggest that the position of the hip joint contributes to controlling hyperactive muscle activity.…

Measurement of Pressure Distributions as a Function of Seating Parameters

This study examines the effect of seat pan and backrest angles on the distribution of seating pressures. Experimental equipment and data analysis which allow continuous measurement, quantification and analysis of seating pressures on the seat pan and backrest are described. It was found that the seat and backrest angles affected the distribution of pressure on both the seat pan and backrest. The results indicate that increasing the backrest angle was more effective in relieving areas of high pressure than increasing the seat pan angle.