Body-seat Interface Research Articles

Studying mechanical load at body-seat interface during dynamic activities such as wheelchair propulsion: a scoping review

Background The increasing number of wheelchair users and their risk of medical complications such as pressure ulcers (PU) make it important to have a better understanding of their seating characteristics. However, while most studies tackling this issue are based on static measurements, wheelchair users are active in their wheelchairs when performing daily life activities. This suggests the need to assess the mechanical loads at the wheelchair user’s body–seat interface during dynamic activities. Objectives A scoping review was conducted to explore the existing data (shear load and pressure) and highlight significant parameters, relevant conditions and methodological strategies when studying wheelchair users performing a dynamic task. Materials and methods The literature search was performed by applying the PRISMA methodology. Results A total of 11 articles met the inclusion criteria. Differences between static and dynamic data were found in the literature for peak pressure values, pressure distribution and the location of peak pressure. None measured tangential load at the seat/body interface, although two studies measured the shift of the ischial region. A significant impact of the type of pathology has been quantified, showing the need to perform experimental studies on diverse populations. The protocol and the pressure parameters studied were very diverse. Conclusion Further studies carefully choosing interface pressure mapping parameters and investigating a broader range of pathologies are required. Additionally, researchers should focus on finding a way to measure seated tangential load.

A Single Subject, Feasibility Study of Using a Non-Contact Measurement to "Visualize" Temperature at Body-Seat Interface.

Measuring temperature changes at the body-seat interface has been drawing increased attention from both industrial and scientific fields, due to the increasingly sedentary nature from daily leisure activity to routine work. Although contact measurement is considered the gold standard, it can affect the local micro-environment and the perception of sitting comfort. A non-contact temperature measurement system was developed to determine the interface temperature using data gathered unobtrusively and continuously from an infrared sensor (IRs). System performance was evaluated regarding linearity, hysteresis, reliability and accuracy. Then a healthy participant sat for an hour on low/intermediate density foams with thickness varying from 0.5–8 cm while body-seat interface temperature was measured simultaneously using a temperature sensor (contact) and an IRs (non-contact). IRs data were filtered with empirical mode decomposition and fractal scaling indices before a data-driven artificial neural network was utilized to estimate the contact surface temperature. A strong correlation existed between non-contact and contact temperature measurement ( > 0.85) and the estimation results showed a low root mean square error (RMSE) (<0.07 for low density foam and <0.16 for intermediate density foam) and high Nash-Sutcliff efficiency (NSE) values (≈1 for both types of foam materials).

Review of Measuring Microenvironmental Changes at the Body-Seat Interface and the Relationship between Object Measurement and Subjective Evaluation.

Being seated has increasingly pervaded both working and leisure lifestyles, with development of more comfortable seating surfaces dependent on feedback from subjective questionnaires and design aesthetics. As a consequence, research has become focused on how to objectively resolve factors that might underpin comfort and discomfort. This review summarizes objective methods of measuring the microenvironmental changes at the body–seat interface and examines the relationship between objective measurement and subjective sensation. From the perspective of physical parameters, pressure detection accounted for nearly two thirds (37/54) of the publications, followed by microclimatic information (temperature and relative humidity: 18/54): it is to be noted that one article included both microclimate and pressure measurements and was placed into both categories. In fact, accumulated temperature and relative humidity at the body–seat interface have similarly negative effects on prolonged sitting to that of unrelieved pressure. Another interesting finding was the correlation between objective measurement and subjective evaluation; however, the validity of this may be called into question because of the differences in experiment design between studies.

Effects of aircraft seat pitch on interface pressure and passenger discomfort

Seat pitch, defined as the distance from a point on the back of one seat to the same point on the seat in front, is one of the most important factors influencing aircraft seating comfort. This study assessed the influence of different airline seat pitches on subjective ratings of discomfort and body-seat interface contact pressures. This was a laboratory within-subjects study using an aircraft interior mock up to vary seat pitch. Twelve participants completed 1 h of sitting in each of five different seat pitches (28inches, 30inches, 32inches, 34inches, and 36inches). Interface pressure mats measured seat and backrest pressure distribution, subjective rating scales were used to measure overall and local body region discomfort. The results showed that overall body and local body region discomfort ratings tend to be lower when the seat pitch increased from 28 inches to 36 inches (p < 0.05). For pressure variables, the upper back average contact area, upper/lower back average contact pressure, upper/lower back average peak contact pressure, right buttock average contact area, left/right thigh buttock average peak contact pressure, and left buttock average peak contact pressure were significantly affected by seat pitch(p < 0.05). Separate analyses support that seat pitch was more strongly correlated with backrest interface pressure than with seat pan pressure. In conclusion, seat pitch was found to be an important factor associated with body-seat contact pressure and discomfort ratings.

Postural Strategies of Bus Drivers During a Regular Work Shift in Urban Area: A Pilot Study

Bus drivers are forced to adopt constrained postures for a long time on a daily basis. This may cause discomfort and, in the long term, represent a co-factor for the onset of musculoskeletal disorders (MSDs), particularly in the low back. Objective measurements of biomechanical variables associated to sitting posture may be useful to better estimate the risk of MSD and, in this context, in recent times in chair movements (ICM) have been shown to represent a reliable tool to characterize sitting postural strategies. This study aimed to evaluate postural strategies of bus drivers during actual long-term driving session in urban area, through the analysis of ICM trend with shift time. Seven professional drivers were tested during regular 6-hours work-shift divided in 50 min point-to-point routes, interspersed by 10 minutes breaks at each last stop. Body-seat interface pressures were collected using a pressure sensitive mat and subjective discomfort rating was evaluated using a 2-parts questionnaire. The results show that, during the whole shift, most drivers report a constant increase in perceived discomfort and a correspondent increase in the overall number of ICM. However, it was interesting to observe that considering a single point-to-point route (i.e. the maximum amount of time in which the drivers must remain seated continuously) the number of ICM increase at the beginning of the period but then decrease significantly, probably when the optimal position to minimize discomfort is reached.

In-Depth Investigation into the Transient Humidity Response at the Body-Seat Interface on Initial Contact Using a Dual Temperature and Humidity Sensor.

Relative humidity (RH) at the body-seat interface is considered an important factor in both sitting comfort and generation of health concerns such as skin lesions. Technical difficulties appear to have limited research aimed at the detailed and simultaneous exploration of RH and temperature changes at the body-seat interface; using RH sensors without the capability to record temperature where RH is recorded. To explore the causes of a spike in RH consistently produced on first contact between body and seat surface, we report data from the first use of dual temperature and RH (HTU21D) sensors in this interface. Following evaluation of sensor performance, the effect of local thermal changes on RH was investigated. The expected strong negative correlation between temperature and RH (R2 = −0.94) supported the importance of considering both parameters when studying impact of sitting on skin health. The influence of sensor movement speed (higher velocity approach: 0.32 cm/s ± 0.01 cm/s; lower velocity approach: 0.17 cm/s ± 0.01 cm/s) into a static RH region associated with a higher local temperature were compared with data gathered by altering the rate of a person sitting. In all cases, the faster sitting down (or equivalent) generated larger RH outcomes: e.g., in human sitting 53.7% ± 3.3% RH (left mid-thigh), 56.4% ± 5.1% RH (right mid-thigh) and 53.2% ± 2.7% RH (Coccyx). Differences in size of RH change were seen across the measurement locations used to study the body-seat interface. The initial sitting contact induces a transient RH response (duration ≤ 40 s) that does not accurately reflect the microenvironment at the body-seat interface. It is likely that any movement during sitting would result in similar artefact formation. As a result, caution should be taken when investigating RH performance at any enclosed interface when the surfaces may have different temperatures and movement may occur.

Dynamic forces over the interface between a seated human body and a rigid seat during vertical whole-body vibration

Biodynamic responses of the seated human body are usually measured and modelled assuming a single point of vibration excitation. With vertical vibration excitation, this study investigated how forces are distributed over the body-seat interface. Vertical and fore-and-aft forces were measured beneath the ischial tuberosities, middle thighs, and front thighs of 14 subjects sitting on a rigid flat seat in three postures with different thigh contact while exposed to random vertical vibration at three magnitudes. Measures of apparent mass were calculated from transfer functions between the vertical acceleration of the seat and the vertical or fore-and-aft forces measured at the three locations, and the sum of these forces. When sitting normally or sitting with a high footrest, vertical forces at the ischial tuberosities dominated the vertical apparent mass. With feet unsupported to give increased thigh contact, vertical forces at the front thighs were dominant around 8Hz. Around 3–7Hz, fore-and-aft forces at the middle thighs dominated the fore-and-aft cross-axis apparent mass. Around 8–10Hz, fore-and-aft forces were dominant at the ischial tuberosities with feet supported but at the front thighs with feet unsupported. All apparent masses were nonlinear: as the vibration magnitude increased the resonance frequencies decreased. With feet unsupported, the nonlinearity in the apparent mass was greater at the front thighs than at the ischial tuberosities. It is concluded that when the thighs are supported on a seat it is not appropriate to assume the body has a single point of vibration excitation.

Performance Assessment of a Humidity Measurement System and Its Use to Evaluate Moisture Characteristics of Wheelchair Cushions at the User-Seat Interface.

Little is known about the changes in moisture that occur at the body–seat interface during sitting. However, as increased moisture can add to the risk of skin damage, we have developed an array of MEMS (Micro-Electro-Mechanical System) humidity sensors to measure at this interface. Sensors were first evaluated against traceable standards, followed by use in a cross-over field test (n = 11; 20 min duration) using different wheelchair cushions (foam and gel). Relative humidity (RH) was measured at the left mid-thigh, right mid-thigh and coccyx. Sensors were shown to be unaffected by loading and showed highly reliable responses to measured changes in humidity, varying little from the traceable standard (<5%). Field-test data, smoothed through a moving average filter, revealed significant differences between the three chosen locations and between the gel and foam cushions. Maximum RH was attained in less than five minutes regardless of cushion material (foam or gel). Importantly, RH does not appear to distribute uniformly over the body–seat interface; suggesting multiple sensor positions would appear essential for effectively monitoring moisture in this interface. Material properties of the cushions appear to have a significant effect on RH characteristics (profile) at the body–seat interface, but not necessarily the time to peak moisture.

Design and development of a thermal imaging system based on a temperature sensor array for temperature measurements of enclosed surfaces and its use at the body-seat interface

Abstract We describe a mapping system based on 64 evenly spaced digital sensors (thermal in this example) and interpolation algorithms. Current pressure mapping systems are suspect to noise, signal drift (creep), hysteresis and drop out of pixels, requiring frequent recalibration all of which impact on accuracy and experimental protocols. The system described here uses a one-wire-based protocol for easy configuration and reliable measurement without requiring frequent recalibration and can continuously measure temperature over a surface (seat or mattress) for hours. Additionally, in this example, the system can be used to overcome inherent drawbacks of traditional temperature (or humidity) assessment, being capable of mapping entire regions simultaneously. It greatly outperforms visual imaging (i.e. infrared) techniques at enclosed surfaces. The system, as shown here, could prove invaluable in future development of monitoring systems as it allows for more accurate parameter modelling at enclosed surfaces such as the body-seat interface. This will be useful when creating more realistic understanding of the changes occurring and how to moderate them effectively in order to reduce problems associated with prolonged wheelchair use.

The effect of cushion properties on skin temperature and humidity at the body-support interface

ABSTRACTThe purpose of this study is to explore the effects of various cushions on skin temperature and moisture at the body–seat interface during a 2-hour period of continuous sitting. Seventy-eight participants were randomly assigned to sit on one of the three types of wheelchair cushions for unrelieved sitting for over 2 hours. Skin temperature and relative humidity (RH) were measured under the subjects’ ischial tuberosities and thighs bilaterally with digital temperature and humidity sensors. Data were collected before sitting and at 15-minute intervals thereafter. Participants sitting on foam–fluid hybrid cushions showed significantly lower skin temperatures than those sitting on air-filled and foam cushions (p < 0.05), but RH did not differ significantly among the cushions (p = 0.97). The three cushions produced a similar increasing trend in RH over time and RH reached a plateau during the 2-hour sitting period. To select the appropriate wheelchair cushion, the microclimate (heat and moisture control) between the body–seat interface should be considered as well as pressure distribution. In comparison with foam–fluid hybrid cushions, the air-filled rubber and foam cushions tended to increase skin temperature by several degrees after prolonged sitting. However, cushion materials did not have significant differences in moisture accumulations.

Evaluation of the Functional and Non-functional Seat Sponge Effect in Sitting Chairs

Objective: The purpose of this study was to evaluate comfort levels of functional and non-functional chairs using subjective comfort rating, interface pressure measurement, muscle activity measurement, and skin temperature measurement.<BR><BR> Background: Chairs are used for a prolonged period of time for sitting in many places such as the office, at university, at school, in industry, and so on. Almost all people use chairs in their everyday life. The functional properties of the chair are associated with comfort.<BR><BR> Method: The subjective evaluation contains questions regarding chair comfort which can be rated with five point scale. The body-seat interface pressure was measured using a pressure mat system. The symmetry of sitting was measured using electromyography. The change in body part (thigh and buttock) temperature before and after sitting on a chair was measured with an infrared camera.<BR><BR> Results: Participants rated significantly (p < 0.05) higher comfort scores for the functional chair in relation to the buttock and thigh region. Also, the participants felt a better cushion effect in the functional chair. When using the functional chair, lower interface pressure, better thermal comfort, and better symmetry of erector spinae muscle activity were observed.<BR><BR> Conclusion: Overall, interface pressure measurement, muscle activity measurement, thermal imaging and subjective comfort score results showed that the functional chair was more comfortable than the non-functional chair.<BR><BR> Application: The adopted methodologies could be used to measure the seating comfort of train seats.

Express Train Seat Discomfort Evaluation using Body Pressure and Anthropometric Data

Objective: The purpose of this study was to evaluate Koreas Honam express trains first- and second-class seat discomfort by using pressure measurement, subjective discomfort rating, and physical compatibility. Background: Over the years, the demand for an express train service is continually increasing. A comfortable ride is important to achieving passenger satisfaction. A train seat plays a significant role in fulfilling passenger seating comfort. With this in view, a field survey and pressure measurements were performed on the selected train seat. Method: The pressure ratio at the body-seat interface (thigh and buttock regions) was measured by the pressure mat system. The interface pressure ratio was calculated and compared. The subjective discomfort rating scale was used to evaluate the overall feeling. The dimensions of train seats were analysed according to the anthropometric and demographic characteristics of the population data from Size Korea. Results: The results highlighted that the interface pressure ratio was greater while participants sat on the second-class seat than the first-class seat in the left- and right-side thigh regions. Also the pressure ratio was greater for the participants in the 1st~25th percentile height groups (149.8~160.8cm). The subjects rated higher discomfort for the second-class seat than the first-class seat. The physical compatibility results showed that the second-class seat’s breadth was inadequate for the 95th and 99th percentile male. Conclusion: Overall, interface pressure measurement, subjective discomfort score and physical compatibility results showed that the second-class seat was more uncomfortable for the passengers than the first-class seat. Application: The adopted methodologies could be used to measure the seating comfort of the train seats.

Dynamic modeling of seated human body based on measurements of apparent inertia matrix for fore-and-aft/vertical/pitch motion

Various models of a seated human body have been developed in the literature so far based on measurements of apparent mass in the vertical Z-direction alone or fore-and-aft X-direction alone. As the authors observed that accelerations in both X and Z directions are equally significant in tests on an excavator working in a quarry, 3×3 apparent inertia matrix was experimentally obtained as functions of frequency by exciting the seated human body in the Z– X plane, i.e. providing two translational motions in the Z and X axes and one angular motion about the Y-axis. A subject in slightly slouched posture was sitting on a seat without backrest and the hands were on lap. Five resonances were found in the frequency range of interest, i.e. up to 20 Hz, below 1 Hz and at 3, 5.25, 8, 9.5 Hz, which is one more than four resonances found in previous researches. The resonance at 8 Hz was newly found in only pitch component of the apparent inertia matrix. Since the experiment was carried out only for one subject, it may not be guaranteed that the new resonance is generally applicable. A 5-degree-of-freedom (dof) model with 23 parameters is proposed for the description of the apparent inertia matrix of a seated human body. The 8 geometric parameters were included in the model in order to describe the couplings between coordinates. The model yielded the resonances at 0.61, 3.3, 5.1, 8.8 and 9.8 Hz, which are near to observations of the experiment. The parameters of the models may not necessarily represent the physical values of a human body because only the apparent inertia matrix at human body–seat interface was reflected. The model may not be perfect because the apparent inertia matrix was obtained from only one subject. Yet, the observations and the model in this research could be a guideline or reference in future researches to obtain more perfect models. Since the vibration responses in the Z– X plane at the human–seat interface can be predicted using the proposed 5-dof model, this model could be used for evaluation of a seat system by computer simulations from the aspect of ride comfort and health.

Gender- and time-varying postural and discomfort responses during prolonged driving

The objective of this study was to conduct gender- and time-based comparisons of postural and discomfort responses during prolonged simulated driving. Prolonged driving has been linked with low back disorders (LBD), however underlying mechanisms of pain or injury are not well understood despite many efforts to delineate the biomechanics of automobile seating. Twelve males and 12 females were exposed to one hour of simulated automobile driving. Body postures, body-seat pressure distributions, and ratings of perceived discomfort were documented and gender- and time-based comparisons were performed. Females exhibited approximately 10° greater changes in lumbo-pelvic orientation when upright standing postures were compared to those in automobile seating. Attributed to gender-based differences in body size was the finding that males experienced significantly greater body-seat interface pressures. Many of the postural, pressure, and discomfort measures varied significantly over 30 to 45 minutes, and these variations were mostly consistent between genders. Many variables examined varied as a function of gender and duration of driving. Future biomechanical investigations of automobile seating design for more effective LBD prevention should consider these potential effects in order to gain further insight into potential low back pain- or injury-generating mechanisms.

Biodynamic Response and Spinal Load Estimation of Seated Body in Vibration Using Finite Element Modeling

Trunk biomechanical models play an indispensable role in predicting muscle forces and spinal loads under whole-body vibration (WBV) exposures. Earlier measurements on the force-motion biodynamic response (impedance, apparent mass) at the body-seat interface and vibration transmissibility (seat to head) have led to the development of different mechanical models. Such models could simulate the overall passive response and serve as an important tool for vehicle seat design. They cannot, however, evaluate physiological parameters of interest under the WBV. On the contrary, anatomical models simulating human's physiological characteristics can predict activities in muscles and their dynamic effects on the spine. In this study, a kinematics-driven nonlinear finite element model of the spine, in which the kinematics data are prescribed, is used to analyse the trunk response in seated WBV. Predictions of the active model (i.e., with varying muscle forces) as compared with the passive model (i.e., with no muscle forces) compared satisfactorily with measurements on vertical apparent mass and seat-to-head transmissibility biodynamic responses. Results demonstrated the crucial role of muscle forces in the dynamic response of the trunk. Muscle forces, while maintaining trunk equilibrium, substantially increased the compression and shear forces on the spine and, hence, the risk of tissue injury.

Assessment of mechanical conditions in sub-dermal tissues during sitting: A combined experimental-MRI and finite element approach

A common but potentially severe malady afflicting permanent wheelchair users is pressure sores caused by elevated soft tissue strains and stresses over a critical prolonged period of time. Presently, there is paucity of information regarding deep soft tissue strains and stresses in the buttocks of humans during sitting. Strain and stress distributions in deep muscle and fat tissues were therefore calculated in six healthy subjects during sitting, in a double-donut Open-MR system, using a “reverse engineering” approach. Specifically, finite element (FE) models of the undeformed buttock were built for each subject using MR images taken at the coronal plane in a non-weight-bearing sitting posture. Using a second MR image taken from each subject during weight-bearing sitting we characterized the ischial tuberosity sagging toward the sitting surface in weight-bearing, and used these data as displacement boundary conditions for the FE models. These subject-specific FE analyses showed that maximal tissue strains and stresses occur in the gluteal muscles, not in fat or at the skin near the body–seat interface. Peak principal compressive strain and stress in the gluteus muscle were 74±7% and 32±9 kPa (mean±standard deviation), respectively. Peak principal compressive strain and stress in enveloping fat tissue were 46±7% and 18±4 kPa, respectively. Models were validated by comparing measured peak interface pressures under the ischial tuberosities (17±4 kPa) with those calculated by means of FE (18±3 kPa), for each subject. This is the first study to quantify sub-dermal tissue strain and stress distributions in sitting humans, in vivo. These data are essential for understanding the aetiology of pressure sores, particularly those that were recently termed “deep tissue injury” at the US National Pressure Ulcer Advisory Panel (NPUAP) 2005 Consensus Conference.

Evaluation of driver's discomfort and postural change using dynamic body pressure distribution

The main objective of this study is the application of body pressure distribution measurements for the prediction of the driver's posture and its change. This requires quantitative analyses of dynamic body pressure distribution, which is the change of body pressure distribution with time. To investigate the relationship between dynamic body pressure data with driver's posture, 16 male subjects performed a simulated driving task for 45 min in a seating buck. During driving, the body posture and body-seat interface pressure were measured continuously, and the discomfort ratings were surveyed at the prescribed interval. For the statistical analyses, driving period, stature group, and lumbar support prominence were selected as independent variables, whereas subjective ratings of driver discomfort, driving posture, and body pressure values were selected as dependent variables. In this study, newly defined dynamic body pressure distribution variables were proposed, and the relationship between these pressure variables with subjective discomfort ratings were analyzed. The close correlations between the body pressure change variables and subjective discomfort ratings supported the possibility of using dynamic pressure data as a tool for the assessment of driver discomfort. Relevance to industry Since dynamic body pressure distribution data provide quantitative and objective indices in measuring driver's postural changes and discomfort while driving, the proposed method can be used for more effective automobile seat design and its evaluation.

Development and Evaluation of a New Body-Seat Interface Shape Measurement System

A new system has been developed to capture the body-seat interface shape. It can repeatedly and accurately measure interface deformation. The shape sensing array system uses optical fiber technology and is noninvasive. The system can cover an interface as large as 400 x 480 mm and the shape is measured over a 10 x 12 array of sensors laminated on ribbon substrates. The accuracy and repeatability of this system were assessed. Measurement errors were evaluated by comparing the shape with a reference shape obtained by a mechanical digitizer. The root-mean-square error in the Z direction for the system was 3.79 mm. The repeatability of the system was within 0.38 mm under controlled conditions. Different interface materials noticeably affected measurements. With the development of this interface shape measurement device, the basic information gathered through its use may prove to be fundamental in the successful design of generic-shape contoured support surfaces. Furthermore, we expect that the new shape measurement device will provide a quick and effective tool for cushion evaluation and clinical guidelines for cushion prescription.

The influence of seat adjustment and a thoraco-lumbar-sacral orthosis on the distribution of body-seat pressure in children with scoliosis and pelvic obliquity

Purpose: To determine the effect of a thoraco-lumbar-sacral orthosis (TLSO) on the distribution of body-seat interface pressure in children with concomitant scoliosis and pelvic obliquity and to determine the effects of two methods commonly used in customized seating—elevation (push up) of the lower side of the pelvis or a wedge insertion beneath the raised pelvis—on the distribution of body-seat interface pressure.Methods: The study population comprised 15 children with an underlying neuromuscular disorder. All had scoliosis and pelvic obliquity when seated, and used a TLSO during sitting. Body-seat interface pressure was measured using the QA Pad. Maximum pressure, mean pressure and contact area were recorded at baseline and at 10° ‘push up’ and 10° wedge insertion, with and without the TLSO. X-rays were performed with and without the orthosis at baseline position.Results: The TLSO reduced the scoliosis deformity by a mean of 5.3 degrees and significantly (p < 0.05) reduced the mean pressure and contact area in the sub-group of patients whose pelvic obliquity was contralateral to the side of the curve. Seat adjustment did not have any significant effect on pressure readings.Conclusion: Application of a TLSO in a child with scoliosis and contralateral pelvic obliquity significantly reduced the spinal curvature and interface sitting pressure. Manipulation of sitting by use of wedges under the pelvis had no significant effect on pressure distribution.

Analysis of pressure distribution at the body–seat interface in able-bodied and paraplegic subjects using a deformable active contour algorithm

In this paper, a semi-automatic method for segmenting pressure distribution image-based data at the body–seat interface is presented. The purpose of this work was to estimate the surface and the load supported by the ischial tuberosity (IT) region. The proposed method involves three steps: (1) detecting the IT region using a pressure-distribution image gradient; (2) estimating the contour of the IT region by an iterative active contour algorithm and finally (3) estimating the percentage of the surface and the weight-bearing of the IT region in a group of able-bodied (AB) and spinal-cord injury (SCI) subjects. It was found in this study that the weight bearing on the IT for the spinal-cord injured group is distributed on half the surface in comparison with the AB group or the powered wheelchair users groups. The findings of this study provide insights concerning pressure distribution in sitting for the paraplegic and able-bodied.