Effects of In-Wheel Suspension on Whole-Body Vibration and Comfort in Manual Wheelchair Users

Misch J.P., Liu Y., Sprigle S.

Manual wheelchair users are exposed to whole-body vibrations as a direct result of using their wheelchair. Wheels, tires, and caster forks have been developed to reduce or attenuate the vibration that transmits through the frame and reaches the user. Five of these components with energy-absorbing characteristics were compared to standard pneumatic drive wheels and casters. This study used a robotic wheelchair propulsion system to repeatedly drive an ultra-lightweight wheelchair over four common indoor and outdoor surfaces: linoleum tile, decorative brick, poured concrete sidewalk, and expanded aluminum grates. Data from the propulsion system and a seat-mounted accelerometer were used to evaluate the energetic efficiency and vibration exposure of each configuration. Equivalence test results identified meaningful differences in both propulsion cost and seat vibration. LoopWheels and SoftWheels both increased propulsion costs by 12-16% over the default configuration without reducing vibration at the seat. Frog Legs suspension caster forks increased vibration exposure by 16-97% across all four surfaces. Softroll casters reduced vibration by 11% over metal grates. Wide pneumatic ‘mountain’ tires showed no difference from the default configuration. All vibration measurements were within acceptable ranges compared to health guidance standards. Out of the component options, softroll casters show the most promising results for ease of efficiency and effectiveness at reducing vibrations through the wheelchair frame and seat cushion. These results suggest some components with built-in suspension systems are ineffective at reducing vibration exposure beyond standard components, and often introduce mechanical inefficiencies that the user would have to overcome with every propulsion stroke.

Misch J., Sprigle S.

Whole-body vibration (WBV) experienced during manual wheelchair use was quantified across several types of terrain (tile, sidewalk, decorative bricks, expanded metal grates). Over-ground travel was controlled using a robotic propulsion system. Vibrations along the vertical axis were measured with a triaxial accelerometer mounted to the seat of the wheelchair. Root-mean-square acceleration values were compared to the health guidance exposure limits established by the European Council using the WBV calculator tool published by the Health and Safety Executive (HSE). Vibrations along the vertical axis were well below the exposure values associated with health risks. Even the most aggressive tactile surface (grates) tested in this study would require more than 14 h of daily travel to reach the “exposure action value,” and more than 24 h would be required to reach the “exposure limit value”. Considering the average cumulative duration of active self-propulsion among manual wheelchair users is around an hour or less, none of the tested conditions were deemed unsafe or damaging.

Lariviere O., Chadefaux D., Sauret C., Thoreux P.

Manual wheelchair (MWC) propulsion can expose the user to significant vibration. Human body exposure to certain vibrations can be detrimental to health, and a source of discomfort and fatigue. Therefore, identifying vibration exposure and key parameters influencing vibration transmissibility during MWC propulsion is crucial to protect MWC users from vibration risks. For that purpose, a systematic review using PRISMA recommendations was realized to synthesize the current knowledge regarding vibration transmissibility during MWC propulsion. The 35 retrieved articles were classified into three groups: Vibration content, parameters influencing vibration transmission, and vibration transmission modeling. The review highlighted that MWC users experience vibration in the frequency range detrimental/uncomfortable for human vibration transmission during MWC propulsion depends on many parameters and is still scarcely studied and understood. A modeling and simulation approach would be an interesting way to assist physicians in selecting the best settings for a specific user, but many works (modeling, properties identification, etc.) must be done before being effective for clinical and industrial purposes.

Giwnewer U., Rubin G., Friedman A., Rozen N.

Background: Many Wheelchair users experience adverse effects specific to their situation, some of which might be avoided if suspension systems are integrated into the wheelchair. Objectives: Our study aimed to compare the user experience using a novel wheelchair suspension system with normal wheels. We tried to quantify the user feelings and impressions while using the different wheels. Study Design: Double blinded comparative randomized study. Methods: The patients were randomized into 2 groups. One used shock absorbing wheels, and the other group had a set of standard wheels with the same exact wheelchairs. The patients were taken to a daily trip by the caregivers and given questionnaires in the second and fourth days. On the morning of the third day the wheels were interchanged, creating a cross over between the groups. We collected general and medical information from the participants. The main outcome measures were the questionnaires filled by the patients and the caregivers aiming to quantify the user experience with the suspension equipped wheels. Results: Statistical significance was reached in 2 questions referred to the patients: “In general—During the ride I didn’t feel the bumps” and “I feel very confident when riding the chair” and in one question referred to the caregiver—“It was easy to push the chair in suboptimal ground.” Conclusions: We conclude that the shock absorbing system provided a better user experience in the immediate term than standard wheels. Further study is needed to assess the long-term implications.

Orelaja O.A., Wang X., Ibrahim D.S., Sharif U.

Vibration is experienced when a body is subjected to either internal or external forces which cause oscillation, with most operators of industrial equipment often exposed to high dosage, higher than the stipulated values. In this research, Digital Real-Time Frequency Analyzer (RSA 5106A) was used, while the results obtained were evaluated and compared with the health guidelines of the ISO 2631-1 : 1997 and ISO 2631-5 : 2004 standards, as described in the Health Guidance Caution Zone for a daily exposure action value (EAV) of 0.47 m/s2 and a daily exposure limit value (ELV) of 0.93 m/s. High acceleration was mostly seen on the z-axis in all the results obtained, whereas many were not within the HGCZ (Arms <0.47, and >0.93 m/s2). Comparing (VDV <8.5 m/s1.75 and >17 m/s1.75) with the ISO standard, the accelerations on all x- and y-axes were slightly within the HGCZ, with just a little below 0.47 m/s2 limit. The results obtained clearly showed that urgent action is needed virtually on all the equipment in both the Secondary Manufacturing Department (SMD) and Primary Manufacturing Department (PMD) to minimize vibration exposure on the technical operators.

Ahram T., Karwowski W., Taiar R.

The original version of the book was inadvertently published with incorrect copyright names in Chapters “Measuring collaborative emergent behavior in multi-agent reinforcement learning”.

Hischke M., Reiser R.F.

Suspension systems are designed to reduce shock and vibration exposure. An aftermarket rear-wheel suspension system is now available for manual tilt-in-space wheelchairs.To compare quantifiable shock and vibration on a rigid manual tilt-in-space wheelchair to published data on manual wheelchairs and to determine whether aftermarket rear suspension system will significantly decrease shock exposure when traversing common obstacles.Cross-sectional.Research laboratory.Ten healthy non-wheelchair users.Subjects seated in a manual tilt-in-space wheelchair were pushed over 4 different obstacles (an exterior door threshold, truncated domes, 2-cm descent, and 2-cm ascent) with the chair as manufactured and with the suspension system installed.Superior/inferior and anterior/posterior accelerations were assessed at the seat pan with and without the use of ISO 2631-1 standards. Peak accelerations were analyzed from the door threshold, 2-cm descent and 2-cm ascent. Root mean square acceleration (RMSa) values were analyzed from the truncated domes, and vibration dose value (VDV) was analyzed for all surfaces.There were no differences in time spent over the 4 obstacles between rigid and suspended conditions (P≥.064). Suspension decreased the peak acceleration at the rear wheel when it initially impacted the door threshold, and when the rear wheel traversed the 2-cm descent and ascent (P≤.043). ISO 2631-1 frequency weighting, placing emphasis on frequencies most harmful to humans, also supports suspension reducing peak accelerations at the rear wheel both when it initially impacted and left the door threshold, and when the rear wheel descended 2 cm (P≤.049). Suspension also reduced the truncated dome RMSa as well as the door threshold, 2-cm descent, and total VDV (P≤.041).The results indicate that rigid manual tilt-in-space wheelchairs respond to rough surfaces in a similar fashion to previously studied rigid wheelchairs. Furthermore, the aftermarket suspension system reduces some aspects of shock and vibration exposure, also consistent with previously studied suspension systems.NA.

Duvall J., Sinagra E., Cooper R., Pearlman J.

In the United States, over three million people use a wheelchair for their primary means of mobility and they rely on functional and accessible pathways to participate in their communities. The Americans with Disabilities Act Accessibility Guidelines related to pathway roughness are currently ambiguous, subjective and therefore unable to be measured. Consequently, many public pathways are sufficiently rough to result in harmful vibrations and discomfort for wheelchair users. In previous research, subjective ratings and root-mean-square accelerations were reported from subjects traveling over surfaces with various roughnesses in their own wheelchairs. The purpose of the current study is to use previous data to propose roughness thresholds by correlating the roughness of surfaces to vibration data and subjective ratings from wheelchair users. The results suggest a pathway roughness index threshold of ≤50 mm/m (1.2 in./ft) for a surface segment of 100 m (328 ft) in length, and ≤100 mm/m (1.2 in./ft) for a surface segment of 3 m (9.8 ft) in length would protect wheelchair users against discomfort and possible health risks due to vibration exposure. For surfaces of different lengths, a 3 m (9.8 ft) and 100 m (328 ft) moving window should be used.

Herrick J.E., Flohr J.A., Wenos D.L., Saunders M.J.

Purpose:This study compared the metabolic and performance effects of riding front-only suspension (FS) and front-and-rear suspension (FRS) mountain bicycles on an off-road course that simulated competitive cross-country race conditions (>105 min in duration, with ∼70% of time spent riding uphill).Methods:Seven competitive mountain bikers (73.8 ± 7.6 kg; 61.0 ± 4.3 mL·kg–1·min–1) completed two randomized FS and FRS trials. Bikes were similar, excluding rear wheel suspension on the FRS, which increased bike weight by ∼2 kg. Each trial consisted of four laps of rugged 8 km trail with 154 m of elevation gain per lap. The first three laps were performed at ∼70% of VO2max; VO2, HR, and RPE were collected during the first and third laps. The final lap was performed as a maximal time-trial effort.Results:During the first and third laps, VO2, HR, and RPE were similar between FS and FRS. However, FS was significantly faster than FRS during the ascending segment of the course (17.6 ± 2.9 vs 18.9 ± 3.4 min,P= .035), despite similar VO2(P= .651). Although not statistically significant, FRS tended to be faster than FS during the descending portion of the course (8.1 ± 2.0 vs 9.1 ± 2.1,P= .067) at similar VO2. Performance during the final time-trial lap was significantly faster for FS than FRS (24.9 ± 3.9 min, 27.5 ± 4.9 min,P= .008).Conclusion:FS was faster than FRS over a course that simulated competitive cross-country race conditions. The faster times were likely the result of improved cycling economy during ascending, which were at least partially influenced by the lighter weight of the FS.

Chénier F., Aissaoui R.

Wheelchair propulsion exposes the user to a high risk of shoulder injury and to whole-body vibration that exceeds recommendations of ISO 2631-1:1997. Reducing the mechanical work required to travel a given distance (WN-WPM, weight-normalized work-per-meter) can help reduce the risk of shoulder injury, while reducing the vibration transmissibility (VT) of the wheelchair frame can reduce whole-body vibration. New materials such as titanium and carbon are used in today’s wheelchairs and are advertised to improve both parameters, but current knowledge on this matter is limited. In this study, WN-WPM and VT were measured simultaneously and compared between six folding wheelchairs (1 titanium, 1 carbon, and 4 aluminium). Ten able-bodied users propelled the six wheelchairs on three ground surfaces. Although no significant difference of WN-WPM was found between wheelchairsP<0.1, significant differences of VT were foundP<0.05. The carbon wheelchair had the lowest VT. Contrarily to current belief, the titanium wheelchair VT was similar to aluminium wheelchairs. A negative correlation between VT and WN-WPM was found, which means that reducing VT may be at the expense of increasing WN-WPM. Based on our results, use of carbon in wheelchair construction seems promising to reduce VT without increasing WN-WPM.

Garcia-Mendez Y., Pearlman J.L., Boninger M.L., Cooper R.A.

Sonenblum S.E., Sprigle S., Lopez R.A.

Background. This study aimed to describe how people move about in manual wheelchairs (MWCs) during everyday life by evaluating bouts of mobility or continuous periods of movement.Methods. A convenience sample of 28 MWC users was recruited. Participants' everyday mobility was measured using a wheel-mounted accelerometer and seat occupancy switch for 1-2 weeks. Bouts of mobility were recorded and characterized.Results. Across 29,200 bouts, the median bout lasted 21 seconds and traveled 8.6 m at 0.43 m/s. 85% of recorded bouts lasted less than 1 minute and traveled less than 30 meters. Participants' daily wheelchair activity included 90 bouts and 1.6 km over 54 minutes. Average daily occupancy time was 11 hours during which participants wheeled 10 bouts/hour and spent 10% of their time wheeling. Spearman-Brown Prophecy analysis suggested that 7 days were sufficient to achieve a reliability of 0.8 for all bout variables.Conclusions. Short, slow bouts dominate wheelchair usage in a natural environment. Therefore, clinical evaluations and biomechanical research should reflect this by concentrating on initiating movement, maneuvering wheelchairs, and stopping. Bouts of mobility provide greater depth to our understanding of wheelchair use and are a more stable metric (day-to-day) than distance or time wheeled.

Racine J.S.

1. OVERVIEW One frequently voiced complaint about the R programming environment (R Development Core Team, 2011) is its rather ‘clunky’ user interface and the fact that multiple interfaces exist and differ across platforms. Even seasoned R users acknowledge that there is room for improvement, and there have been a number of attempts made to create a more user-friendly interface. However, it is widely acknowledged that there remains room for improvement in this area. Users of R also tend to be users of , and a small but growing subset tend also to be users of Sweave. It is safe to say that interface-related complaints levied against R are also tossed at and Sweave for similar (and often well-justified) reasons. However, a recent entrant is poised to resolve these issues not only for R but also for this trifecta of programs that tend to be jointly used by econometricians and academics (i.e. R, Sweave, and ). The new entrant is titled ‘RStudio’ (see www.rstudio.org). It is currently in beta status (version 0.94 (RStudio Beta 3) as of this writing) and was publicly released on 28 February 2011. However, it is quite stable and currently suitable for general use. Like R, it is free and open. This review discusses the aspects of RStudio that are likely to be of most interest to econometricians. Naturally, this would also be of interest to academics using R in the classroom, as students would likely be more comfortable with this interface than existing ones, while the platform-independent nature would minimize cross-platform issues encountered by new users.

Boninger M.L., Cooper R.A., Fitzgerald S.G., Lin J., Cooper R., Dicianno B., Liu B.

Despite the fact that wheelchair users are exposed to risk factors for neck and upper back pain (NP), little is known about the impact and possible diagnoses associated with NP. The purpose of this study was to examine the significance of NP in wheelchair users and to determine if a portion of the NP may be myofascial in origin.Cross-sectional cohort study using questionnaires and physical exams to evaluate NP in a convenience sample of wheelchair users from the National Veteran's Wheelchair Games. Main outcome measures included reported NP, visual analog scale of neck complaints, Neck Disability Index, and physical examination findings of trigger points.Sixty-six percent of subjects reported NP since becoming a wheelchair user and, 60% reported pain during the past month. Neither age nor length of time in a wheelchair was significantly different between those subjects who did and those subjects who did not report pain. Of those respondents who reported NP, 60% visited the doctor about the pain and 40% limited their daily activities due to the pain. Trigger-point palpation reproduced pain in 54% of those respondents who experienced pain in the past month (n = 34).This study provides a first step in defining the prevalence and significance of NP among wheelchair users. Clinicians who work with this population need to ask subjects about symptoms and consider a myofascial origin for that pain when considering treatment.

Requejo P.S.

Chwalik-Pilszyk G., Cirkl D., Kozien M.S.

In this article, an attempt was made to model the body of a person moving in a passive manner (movement forced by another person) in a wheelchair. For this purpose, the Wan–Schimmels model was modified by 4 DOF, supplementing it with the weight of the wheelchair and a polyurethane cushion. The study was designed to test the effectiveness of utilizing a polyurethane cushion to reduce the whole-body vibration acting on a person while moving in a wheelchair. The study used a rheological model of polyurethane (PU) foam with concentrated parameters. Harmonic and random vibration analysis was carried out for this model. At the same time, the model with 5 DOF seems to be sufficient to describe vibrations transmitted to wheelchair users. The model presented in this paper can become a tool for future analysis of vibrations of people of different weights, moving passively on various types of wheelchairs on surfaces whose irregularities can be given by an appropriate form of kinematic excitation. The approach used in this study is likely to be useful in selecting a wheelchair and seat cushion so as to counteract and minimize vibrations perceived by humans.