# How does moderate upper limb activity modify sitting forces for able-bodied persons and wheelchair users?

Clémence Paquin, Anthony Gelis, Laura Dubuis, Sophie Ciancia, Olivier

Chenu, Sonia Duprey

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Clémence Paquin, Anthony Gelis, Laura Dubuis, Sophie Ciancia, Olivier Chenu, et al.. How does moderate upper limb activity modify sitting forces for able-bodied persons and wheelchair users?. Disability and Rehabilitation: Assistive Technology, 2024, pp.1-9. 10.1080/17483107.2024.2402812. hal-04704266

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Disability and Rehabilitation: Assistive Technology

How does moderate upper limb activity modify sitting forces for able-bodied
persons and wheelchair users?

<table>
   <tr>
    <td>
     Submission ID
    </td>
    <td>
     248334289
    </td>
   </tr>
   <tr>
    <td>
     Article Type
    </td>
    <td>
     Research Article - authors made known to the reviewers
    </td>
   </tr>
   <tr>
    <td>
     Keywords
    </td>
    <td>
     Dynamic, Pressure injuries, normal force, shear force, wheelchair, Peak Pressure Index, spinal cord injury
    </td>
   </tr>
   <tr>
    <td>
     Authors
    </td>
    <td>
     Clemence Paquin, Anthony GELIS, Laura Dubui s, Sophie Ciancia, Olivier Chenu, Sonia Duprey
    </td>
   </tr>
  </table>

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# How does moderate upper limb activity modify sitting forces for able-bodied persons and wheelchair users?

Paquin Clémence<sup>a,b</sup>, Gelis Anthony<sup>c,d</sup>, Dubuis Laura<sup>a</sup>, Sophie Ciancia<sup>e</sup>, Chenu Olivier<sup>b</sup> and Duprey Sonia<sup>a*</sup>

<sup>a</sup> Univ Lyon, Univ Gustave Eiffel, Univ Claude Bernard Lyon 1, LBMC UMR T 9406, F-69622 Lyon, France; <sup>b</sup> T exisense, 71210 Torcy; France; <sup>c</sup> Centre Mutualiste Neurologique Propara, 34090 Montpellier, France; <sup>d</sup> EPSY LON laboratory, 34090 Montpellier, France; <sup>e</sup> Hopital Henry Gabriel, Hospice civil de Lyon, 69200 Lyon, France.

sonia.duprey@univ-lyon1.fr*corresponding author

## Abstract

Most people with a spinal cord injury are concerned by pressure injuries (PrI). Since dynamic activities may involve distributions of forces over time that are different from static and given the significant impact of PrIs on healthcare costs, it is important to study these sitting forces.
We aim to investigate sitting forces (overall normal, shear forces and Peak Pressure Index (PPI)) assessed in both able-bodied and wheelchair users (WCU) under static and dynamic conditions. Our hypothesis is that wheelchair sitting forces encountered by able-bodied participants are significantly different from those of WCUs.

An experimental seat and a pressure mapping system were used to investigate forces in two different populations, 102 able-bodied and 15 WCUs, in static conditions and during synchronized hand-cycling. The analysis includes statistical comparisons of the sitting conditions (static/dynamic) and of the populations (able-bodied/WCUs).

Significant differences in normal forces and PPI were observed between able-bodied and WCUs; conversely, differences in shear forces were non-significant. This suggests that contrary to shear forces, no conclusion on normal forces drawn from trials with healthy participants can directly be applied to WCUs.

Secondly, the present results indicate significant reduced averaged: normal force, PPI, and shear forces for able-bodied performing a dynamic activity compared to static sitting. WCUs
experienced non-significant lower averaged normal force and PPI but significant lower
averaged shear forces.

While the present results seem to indicate lower forces for able-bodied performing a dynamic
activity compared to static sitting, due to reduced averaged forces, this conclusion is less clear-
cut for WCUs.

Keywords: Dynamic, pressure injuries, normal force, shear force, wheelchair, PPI, spinal cord injured

Implication for rehabilitation:

- The present observational study can help understand the specific characteristics of wheelchair users concerning the biomechanical sitting load in rest and during propulsive activity: the shear forces are reduced during activity compared to static conditions.

- From the data collected in the present study, it seems that no conclusion on normal sitting forces drawn from trials with healthy participants can directly be applied to wheelchair users.

Introduction

The number of wheelchair users is on the rise, in line with increased life expectancy [1] which impacts their risk of developing pressure injuries. Among the population with spinal cord injury, the International Spinal Cord Injury Community Survey [2] identifies pressure injuries as the second most prevalent secondary disorder among patients suffering from a spinal cord injury in France. These injuries account for 25% of total healthcare costs for French people with a spinal cord injury and lead to a poorer quality of life [3]. Such social and economic
implications make reducing pressure injury incidence a critical patient priority and a major public health issue. Risk of secondary disorders for people with a spinal cord injury has become a public health challenge [4].

The physiopathology of pressure injuries is intricate, involving both internal and external factors [5,6]. As clinicians can mainly act on external than on internal factors, this study focuses on external variables and more particularly on the mechanical forces: the normal (i.e. perpendicular to the surface) and the shear forces (i.e. parallel to the surface) at the seatpan interface since they are known to play a role in cellular necrosis leading to pressure injuries [7,8]. Whereas sitting normal force has been studied in both static [9–11] and dynamic conditions [12–14] (such as wheelchair propelling), few studies focused on sitting shear force, and those were predominantly conducted in laboratory settings [15,16]. To our knowledge, no studies have measured sitting shear force between the seatpan and the buttocks under dynamic conditions [13].

External mechanical forces during sitting are studied by placing force sensors underneath the seatpan [15], as well as via the commonly used pressure mapping systems [9,11,17–21]. While force sensors provide the normal and shear forces over the entire seatpan, pressure mapping systems reveal the local distribution of pressure on the seatpan. The parameters typically calculated from this pressure distribution are normal force (sum of all sensors) and peak pressure index (PPI, maximum pressure averaged from several sensors in the mapping system) [22]. On the one hand, general parameters such as normal and shear forces offer a comprehensive view of the overall situation within the tissue [21]. On the other hand, more specific parameters like PPI reveal localized pressure, often concentrated around the ischial tuberosity [22]. For clinicians, these parameters offer valuable insights into the internal loading of the tissue [21], considering the causal link between forces at the body-seat interface and internal stress [5,23].

In the healthcare field, clinicians focusing on wheelchair users mainly rely on pressure mapping systems to set up positioning installations. Their major goal is to find a way to reduce either the normal and shear forces, and the PPI. Although most studies involving wheelchair users were conducted in static conditions [13], propelling a wheelchair is a dynamic activity for the wheelchair user, repeated numerous times per day [24]. This suggests the need for studies including dynamic conditions. Among the few existing dynamic studies, some highlighted a decrease in normal forces during wheelchair propulsion [12,14,25–27]. The following question therefore arises: does a dynamic activity such as propelling modify external mechanical forces
in a way to reduce them? Answering this question could contribute to improve recommendations for pressure injury prevention regarding mechanical loads at the body-seat interface.

An issue raised by most experimental studies focusing on seat interface force measurements is the peak pressure discrepancies found between able-bodied participants and wheelchair users. When these differences observed in static conditions [9,14,17] were explored, they were found to be mainly due to morphological causes: there is a major difference in the composition of internal tissues between able-bodied and people with a spinal cord injury [28,29]. Studies focusing on dynamic sitting conditions (while propelling a wheelchair, for instance) did not specifically document differences in sitting forces between able-bodied subjects and wheelchair users [13]. Thus, the following question remains: when wheelchair seat forces are measured at the sitting interface during propelling, do measurements on able-bodied participants accurately represent the force at the seatpan interface experienced by wheelchair users?

This study therefore examines mechanical loads (normal force, shear force, and Peak Pressure Index) under both static and dynamic conditions. We also explore the discrepancies observed between able-bodied participants and wheelchair users, seeking to determine whether findings on the former can be extrapolated to the latter. Our hypothesis is that differences between the sitting forces (normal, shear and PPI) involved in a dynamic activity and in a static trial will vary according to participants' health conditions: able-bodied or wheelchair users.

## Materials and Methods

The protocol was approved by the French Committee for the Protection of Persons (Ouest III, France) and registered as 2021-A03031-40 in March 2022.

## Equipment and Measuring tools

An experimental seat equipped with a 3-dimensional force sensor measurement under the rigid seatpan was used in this experiment to measure shear and normal forces at the body-seat interface [31,33].

This seat could not be equipped with hand rims to reproduce bimanual propulsion. There are some discrepancies between upper limb cycling activity and bimanual propulsion (for instance the latter is not a continuous motion as compared to cycling). Nevertheless, they both have a propulsion stage and a recovery stage [30]. Thus, we chose to equip the experimental seat with
a crankset for hand-cycling (Minibike DOMYOS® 100, Decathlon, France, Figure 1) enabling a forward synchronous movement of both left and right upper limbs with a maximum resistance of 10kg. The experimental seat was also equipped with a wheelchair backrest (Elite®, Matrix, Invacare, Tours, France). A pressure mat (Teximat® from Texisense, Torcy, France) was added to the seatpan to measure pressure distributions (Figure 2) composed of 1024 sensors in an area of 42cm².

## Participant characteristics

102 able-bodied and 15 participants with spinal cord injury or multiple sclerosis were recruited (Table 1). The difference in population size is due to the greater difficulty of recruiting and involving wheelchair users in experiments. It was checked that both populations had a similar body mass index (BMI) (more details in the section “Populations' BMI comparison”). All participants were capable of hand-cycling and able to sit in a chair with a thigh-trunk angle of less than 120° without lateral support.

Participant characteristics were recorded, including wheelchair user condition, BMI, age, weight, height, and sex. For wheelchair users, additional details were collected, including aetiology of neurological disorders (spinal cord injury or multiple sclerosis), neurological level of injury and AIS grade [32] or expanded disability status scale (EDSS) [34].

## Experimental procedure

Able-bodied participants autonomously sat on the experimental seat, while wheelchair users were assisted by a mobile lift. The following adjustments were made to the equipment.

* Adjustments to the experimental seat:

- Seatpan depth was adjusted to ensure maximal contact between the seatpan and the participant's buttocks and thighs,

- Backrest position was adjusted to ensure maximal contact between the backrest and the participant's back,

- The footrest was adjusted so that the participant's feet were flat and legs flexed at 90°.

* Adjustments to the hand crankset:
- The crankset was positioned so that 1/ when the pedals were at their top position, they were aligned with the participant's shoulders; 2/ when the pedals were at the farthest point from the participant, the participant's elbows were flexed at 20°;

- Pedalling resistance was adjusted for each participant to the highest value possible at which the participant could still hand-cycle without taking his/her back off the backrest.

These consignments and adjustments were made to standardise the synchronous **handcycling** movement (resistance and position) due to the heterogeneity of the population of wheelchair users.

Measurements procedure

Once these adjustments were performed, participants had to stand up or lift their bodies from
the seatpan by pushing on the armrests or with assistance, to zero the sensors.

A static measurement (for 5s in a steady state) and a dynamic measurement (for 10s during hand-cycling) were performed (overall, they spent 10 minutes maximum on the seat). To avoid any movement of the upper limb during static measurements, participants were asked to sit hands on knees during the acquisition. For dynamic measurements, the only specific instruction given to participants was to keep their back in contact with the backrest.

The measurement tools (experimental seat force sensors and pressure mapping system) were synchronized through the computer clock, operating at an acquisition frequency of 10Hz, the maximal acquisition frequency of the pressure mapping system.

Outcome

Three parameters were collected from the experimental seat force sensors and from the pressure mapping system, both in static and dynamic conditions:

* Overall antero-posterior Shear Force (SF), i.e. the shear force over the entire seatpan in the antero-posterior direction, measured by the 3-dimensional seat's force sensor (in N).

* Overall Normal Force (NF), i.e. the normal force over the entire seatpan, measured by the 3-dimensional seat's force sensor (in N).

* Peak Pressure Index (PPI), measured with the pressure mapping system for both right and left sides (in kPa). This metric, identified by Maurer et Sprigle [22], is calculated
by averaging the values from the nine sensors surrounding the peak sensor, which
represents a 10cm² area.

For static measurements, the average for each parameter was calculated over the 5-second
acquisition period. For dynamic measurements, since the acquisition frequency did not allow
precise tracking of the cyclic curves, the following metrics (Figure 3) were computed for each
of the three parameters (SF, NF, and PPI):

* Average of recording over the 10s-acquisition,

* Maximum of recording,

* Minimum of recording,

* Range of variation calculated by subtracting the minimum values from the maximum values. When the acquisition frequency does not allow cyclical acquisitions, the range of variation (Figure 3) shows the maximum difference in intensity during the 10s of activity.

These metrics were expressed in N or kPa depending on the parameter and normalized using
their corresponding static measurement (thus presented as a percentage). These normalized
parameters enable comparative analysis of the static and dynamic trials.

The center of pressure (CoP) displacement during the dynamic trials was also calculated from
the pressure map. Since this result is not crucial to the present analysis, it is not shown in Results
but can be found in Supplementary materials.

During the activity, due to low acquisition frequency (lower than hand-cycling frequency), it is
important to note that the maximum, minimum, and shift of the CoP involve measurement
uncertainty.

Statistical procedure

The statistical comparisons were made for both populations between:

1) static (average of the 5s recording) and dynamic (average of the 10s recording)

2) static (average of the 5s recording) and dynamic (maximum of the 10s recording)

The other 4 comparisons were made between able-bodied and wheelchair users for all
conditions and all type of variables: static (averaged variables), dynamic (averaged variables),
dynamic (maximum variables) and dynamic (range of variation of all variables).”
The normality of the dataset was assessed using Shapiro-Wilk tests. Statistical analyses focused on comparative evaluations (static vs dynamic conditions, able-bodied vs wheelchair users).

To compare variables computed under static and dynamic conditions, the Student's paired T-test was used for parametric data (i.e. data following a normal distribution) and the paired Wilcoxon test for non-parametric data (i.e. data not following a normal distribution).

To compare results from the 2 different-sized populations of able-bodied vs wheelchair users, the Welch test was chosen for parametric data and the Mann-Whitney U test for non-parametric data.

# Results

## Statistical normality of data

For data collected during trials with able-bodied participants, normality was found for several parameters: average shear force in static and dynamic conditions and PPI (average) in static. For data collected during trials with wheelchair users, normality was observed for all parameters except range of variation of shear force. The remaining parameters did not pass the normality test and were classified as non-parametric data.

## Populations' BMI comparison

No significant differences in BMI were observed between able-bodied and wheelchair users (p>0.05), confirming their similarity in terms of mass versus height ratio (Table 1).

### Static trials

The data from the static trials with all participants (able-bodied and wheelchair users) showed very similar PPI values (no significant differences found): 32 ± 12 kPa (Table 2). The normal force was about ten times higher than the shear force. These two forces and the PPI showed large standard deviations (about 30%) (Table 2), indicating extensive inter-participant variability in static sitting forces.

### Dynamic trials

As for static results, the normal force was about ten times (average and maximum of the recording) higher than the shear force, and there were high standard deviations (about 30%).
## Statistical comparison between static and dynamic results

The analysis showed that able-bodied participants' normal force and PPI values (average and maximum) measured during dynamic trials were consistently lower than during static trials (Table 4). Their average PPI was approximately 10% lower under dynamic than under static conditions (p<0.05 and p<0.001, respectively). Their normal force was found to be on average 13% lower during dynamic trials (p<0.05). However, wheelchair users showed no significant differences in either PPI or overall normal force between static and dynamic conditions (on average).

Shear force recorded under dynamic conditions was on average significantly lower than that measured under static conditions, by 17% and 27% (p<0.001) respectively for able-bodied and wheelchair users (Table 4).

The maximum shear force recorded under dynamic conditions was significantly higher than static values for able-bodied participants (differences ranging from 10% to 43%, p < 0.001, Table 4). Despite a 25% higher maximum during dynamic than during static trials, the difference was not significant between wheelchair users (Table 4).

In terms of range of variation, normal forces exhibited a relatively small range (23% of the static values) compared to shear force (136% of the static values). More details are shown in Table 3. It is worth noting that the PPI average was situated two-thirds away from the minimum and one-third away from the maximum. On the other hand, shear force was evenly distributed around the average, as shown in Figure 4.

## Differences between populations

Under static conditions, no significant difference in shear forces was found between able-bodied and wheelchair users. However, wheelchair users exhibited a significantly higher average normal force (160 N) and PPI (17 kPa) than able-bodied participants (p<0.05) (Table 5).

Under dynamic conditions, wheelchair users exhibited higher average values for normal force and PPI than able-bodied participants (respectively +202 N, +20 kPa and p<0.001). Wheelchair users also exhibited higher maxima than able-bodied participants for normal force and PPI (respectively, +200N, p<0.05 and + 66kPa p<0.001; Table 6).
# Discussion and conclusion

## Static values

The static values found here were higher (PPI = 33 kPa) than those reported by Aissaoui et al. (PPI = 13 kPa) [17]. This can be explained by the fact that our participants were seated on a rigid seatpan, whereas their participants sat on a flat foam cushion. Compared to other studies where wheelchair users were seated on a rigid seatpan, our PPI values are slightly lower (48 kPa) than those reported by Tam et al. (55 kPa) [14] or Gutierrez et al. (70 kPa) [9]. This could be due to the seatpan material used in our study, which is composed of 52 cylinders, less rigid than the rigid force plate used in the other two studies.

The PPI standard deviations results (about 30kPa) showed similar values as those found by Tam et al. (about 36kPa) and Gutierrez et al. (about 24kPa) [9,14]. These high standard deviations could be explained by the fact that wheelchair users (from spinal cord injury or MS) present multiple differences — anatomical, morphological, and cellular — due to their unique expression of neurological disorders compared to the able-bodied population. Therefore, the generalization of the results from wheelchair users remains complex and controversial.

## Static vs dynamic conditions

The average normal force was lower in the dynamic condition than in the static condition for the able-bodied participants. For bimanual propulsion, Andreoni et al. explained this by a different distribution of the normal forces that was also applied on the handrim during wheelchair propelling [12]. A similar effect could occur here with a partial shift of the force from the seatpan to the crankset and to the feet to ensure stability.

Unfortunately, this result could not be compared with data from the literature, since none of the studies looking at forces in static and dynamic conditions list this parameter [13]. Our population of wheelchair users' PPI dynamic values (average and maximum) were close to their static values (98% ± 11 for the average and 104% ± 10 for the maximum). These PPI values were slightly higher than in the studies conducted by Kernozek and Lewin [35] and Andreoni et al. [12], where PPI dynamic values were respectively 78-100% and 92% of static values. This difference can be attributed to the support for the upper limbs provided by the crankset, which did not allow the same hand support as on hand rims, as explained by Andreoni et al. [12].
In addition, our dynamic values showed a reduction in shear force (on average) in both populations compared with static values. This reduction cannot be compared with the existing literature due to the absence of studies on shear forces during dynamic activities. This reduction cannot be compared with the existing literature due to the absence of dynamic studies on shear forces [13]. An explanation could be that, in dynamic, the participants decreased the normal force applied to the backrest by contracting the core muscles, leading to less shear forces on the seatpan.

## Able-bodied vs wheelchair users

- Differences between participants under static conditions

Wheelchair users exhibited a higher average PPI of +19 kPa (Table 6) than able-bodied participants, consistent with findings in the literature [9,14,17]. The higher average PPI of wheelchair users can be attributed to their higher weights or to more obvious prominences under the ischial tuberosities [28]. Indeed, PPI is closely linked to gluteal morphology, and since spinal cord injury alters this morphology through gluteal amyotrophy, the prominence of ischial supports is accentuated [28].

- Differences between participants under dynamic conditions

Concerning normal forces, wheelchair users exhibited a smaller average reduction (2%) in normal force on the seat during dynamic activity than in static conditions, in contrast to the 9% reduction observed in able-bodied participants. This significant discrepancy can be attributed to the unique characteristics of wheelchair users. Notably, a key distinction between the two populations is their ability to maintain optimal postural control of the trunk. Effective trunk control enhances the efficiency of upper limb activity [36], but wheelchair users lack this ability due to motor deficiency in the abdominal and trunk muscles. This hinders the direct transmission of forces between the upper limbs and the seat. Without such direct transmission, the movements of the upper limbs on the crankset do not lessen the normal forces on the seat as much as for able-bodied participants.

Although the range of variation of the PPI was similar for the two populations, the average of PPI is higher for the wheelchair users than for able-bodied under dynamic conditions.

Regarding averaged shear force, whereas the difference between populations was not significant, dynamic values are 27% lower than static values for wheelchair users compared to 17% lower for the able-bodied participants. We hypothesize that this difference was linked to
the poorer balance of wheelchair users [37]. The wheelchair users' restricted trunk movements observed during upper limb motor activity, driven by the need to maintain balance, support this hypothesis. It is further confirmed by the lower velocity of the CoP and smaller circumference of the circle of the CoP observed for the wheelchair users during activity (supplementary materials).

## Pressure injury risk

Wheelchair users appeared to be at higher risk of pressure injuries than able-bodied participants, since they seemed to sustain higher normal forces and PPI both in static and in dynamic conditions. Furthermore, the evolution of normal forces, PPI, and shear forces between static and dynamic trials seems to differ according to population. Thus, the present results are consistent with our hypothesis: differences in sitting forces involved in static vs dynamic activity vary according to whether participants are able-bodied or wheelchair users. This suggests that no conclusion drawn from trials performed on able-bodied participants should be applied to wheelchair users.

Whereas dynamic activity appears to reduce the risk of pressure injury for able-bodied participants (since it reduces normal force, PPI, and shear force compared to static sitting), this conclusion seems less clear-cut for wheelchair users. Indeed, while wheelchair users showed much lower shear forces (maximum of the recording) during the dynamic than the static trials (a greater reduction than for the able-bodied), their average PPI increased.

Thus, no clear conclusion can be drawn, even though the ranges of variation of normal force and PPI were not centred around the average for wheelchair users (only one-third of variation above the dynamic average, as shown in Figure 5), indicating that the buttock soft tissues were considerably relieved of prolonged loadings.

## Limitations

The first limitation of our study is the low frequency of measurement which can have an impact on our results, especially the maxima (overall normal force, shear force and PPI). The uncertainty couldn't be assessed so these results have to be considered with care.

The dynamic hand-cycling used here does not fully represent a complete 'In-Seat Movement' (total body weight on the seat is reduced by 30%) as defined by Sonenblum and Sprigle [29].
Moreover, it does not represent an actual propulsion gesture. Thus, to fully understand the impact of propulsion, trials with an actual wheelchair still need to be performed.

Furthermore, the intensity of activity is likely to impact results, and only one low intensity with a backrest support was tested here. Moreover, the non-standardised paces of the hand cycling activity, even though there were high and low paces in the sample of each group, could also impact our results. Our conclusions could be broadened by exploring different intensities of activity.

It is important to note that our results depend on the sitting position with a backrest, and that any other propulsive activity without a backrest should have a different effect on the forces at the body-seat interface.

Another limitation of the present study is that participants sat directly on the seatpan whereas almost all wheelchair users place a cushion on the seatpan. This point could affect our results. To be closer to real-life conditions, further experimentations will have to be performed with a cushion on the seatpan.

Finally, the sample size of our two populations is heterogeneous, with more discrepancies in the group of wheelchair users, which makes it difficult to generalize our findings. Nevertheless, each wheelchair user has a unique expression of their neurological disorder. These findings are a first step and should not stop an individual clinical evaluation. In addition, our two populations may suffer from a gender bias, as sex can influence the body composition and subsequently the outcome measures.

## Conclusion

In conclusion, two main results should be noted. Firstly, differences between able-bodied and wheelchair users were observed for normal forces (overall normal force and PPI) and less clear for shear force. Our hypothesis is therefore supported: the difference in the sitting forces (essentially normal) involved during dynamic and static trials varies between able-bodied participants and wheelchair users. Thus, no conclusion drawn from trials with able-bodied participants can directly be applied to wheelchair users regarding normal loads. Secondly, the present results indicate a decrease in mechanical loads for able-bodied participants performing a dynamic activity compared to static sitting, with a reduction in averaged normal force, PPI, and shear force observed.
The evidence is less clear-cut for wheelchair users. While they benefit from alternate unloading of the buttock tissues during a dynamic activity, and from lower averaged shear force, they experience higher averaged PPI.

As a perspective, further *in vivo* studies focusing on biological tissues subjected to alternate loadings could help answer this question.

Disclosure statement

Two of the authors are employed by Texisense, a company producing textile sensors in the context of a PhD project co-supervised by the LBMC laboratory and Texisense.

Funding

This study was partially supported by Texisense.
<figure><img src="image_3.png" /><figcaption>Figure 1: Set-up with a participant and the hand crankset</figcaption></figure>

<figure><img src="image_4.png" /><figcaption>Figure 2: Experimental seat fitted with a wheelchair backrest. The Teximat® is placed on the seatpan in both conditions.</figcaption></figure>

<figure><img src="image_5.png" /><figcaption>Figure 3: Methodological figure: Illustration of the four time's parameters (maximum, minimum, average and range of variation). The signal is in blue.</figcaption></figure>
<table><caption>Table 1: Able-bodied and wheelchair users' characteristics</caption><thead><tr><th></th><th>Wheelchair users</th><th>N = 15</th><th>Able-bodied</th><th>N = 102</th><th>Differences</th></tr></thead><tbody><tr><td>Characteristics</td><td>Mean (±1SD)</td><td>[Min-max]</td><td>Mean (±1SD)</td><td>[Min-max]</td><td></td></tr><tr><td>Age (years)</td><td>40 (12)</td><td>[21-59]</td><td>36 (12)</td><td>[18-64]</td><td>ns</td></tr><tr><td>Sex (male/female)</td><td>16/1</td><td></td><td>55/47</td><td></td><td></td></tr><tr><td>Height (cm)</td><td>177 (8)</td><td>[155-187]</td><td>173 (9)</td><td>[155-191]</td><td>ns</td></tr><tr><td>Weight (kg)</td><td>81 (17)</td><td>[55-110]</td><td>75 (15)</td><td>[48-125]</td><td>p&lt;0,05</td></tr><tr><td>BMI (kg/m²)</td><td>26 (6)</td><td>[16-40]</td><td>24 (4)</td><td>[17-46]</td><td>ns</td></tr><tr><td>Neurological level of injury</td><td>C6-L2</td><td>C6-C8: 2<br>T1-T10: 9<br>T11-L2: 4</td><td></td><td></td><td></td></tr><tr><td>AIS grade</td><td>A: 7<br>B: 5<br>C: 1<br>D: 2</td><td></td><td></td><td></td><td></td></tr><tr><td>Aetiology Multiple sclerosis</td><td>1 (EDSS: 8)</td><td></td><td></td><td></td><td></td></tr><tr><td>Spinal cord injury</td><td>14</td><td></td><td></td><td></td><td></td></tr></tbody></table>

<table><caption>Table 2: Average and standard deviation of parameters in static conditions, for both able-bodied and wheelchair users.</caption><thead><tr><th>Parameters (units)</th><th>Average (±1SD)</th></tr></thead><tbody><tr><td>Shear force (N)</td><td>71 (19)</td></tr><tr><td>Normal force (N)</td><td>638 (183)</td></tr><tr><td>PPI right (kPa)</td><td>34 (12)</td></tr><tr><td>PPI left (kPa)</td><td>30 (12)</td></tr></tbody></table>
**Average of the recording**

<table><thead><tr><th>Parameters (units)</th><th>Average (±1SD)</th><th>% of static (±1SD)</th></tr></thead><tbody><tr><td>Shear force (N)</td><td>56 (23)</td><td>78 (24)</td></tr><tr><td>Normal force (N)</td><td>564 (167)</td><td>89 (9.9)</td></tr><tr><td>PPI right (kPa)</td><td>30 (12)</td><td>90 (12)</td></tr><tr><td>PPI left (kPa)</td><td>30 (12)</td><td>90 (11)</td></tr></tbody></table>

**Maximum of the recording**

<table><thead><tr><th>Parameters (units)</th><th>Average (±1SD)</th><th>% of static (±1SD)</th></tr></thead><tbody><tr><td>Shear force (N)</td><td>97 (35)</td><td>139 (41)</td></tr><tr><td>Normal force (N)</td><td>607 (178)</td><td>95 (10)</td></tr><tr><td>PPI right (kPa)</td><td>33 (12)</td><td>98 (11)</td></tr><tr><td>PPI left (kPa)</td><td>36 (12)</td><td>99 (10)</td></tr></tbody></table>

**Range of variation of the recording (min-max)**

<table><caption>Table 3: Average, maximum, and range of variation (min-max) of parameters during the activity in N or kPa and in % of the static condition, for both able-bodied and wheelchair users.</caption><thead><tr><th>Parameters (units)</th><th>Average (±1SD)</th><th>% of static (±1SD)</th></tr></thead><tbody><tr><td>Shear force (N)</td><td>90 (57)</td><td>136 (91)</td></tr><tr><td>Normal force (N)</td><td>113 (65)</td><td>18 (9)</td></tr><tr><td>PPI right (kPa)</td><td>8.31</td><td>23 (14)</td></tr><tr><td>PPI left (kPa)</td><td>7 (5)</td><td>23 (15)</td></tr></tbody></table>

<figure><img src="image_6.png" /><figcaption>Figure 4: Distribution of the range of variation as a function of the recording average</figcaption></figure>
Average of the recording

<table><thead><tr><th rowspan="2">Parameters (units)</th><th colspan="2">Able-bodied</th><th colspan="2">Wheelchair users</th></tr><tr><th>Significance (p-value)</th><th>Difference unit (%)</th><th>Significance (p-value)</th><th>Difference unit (%)</th></tr></thead><tbody><tr><td>Shear force (N)</td><td>p&lt;0.001</td><td>-15 (-17%)</td><td>p&lt;0.001</td><td>-21 (-27%)</td></tr><tr><td>Normal force (N)</td><td>p&lt;0.05</td><td>-79 (-13%)</td><td>ns</td><td>-35 (-2%)</td></tr><tr><td>PPI right (kPa)</td><td>p&lt;0.05</td><td>-3 (-11%)</td><td>ns</td><td>-1 (-4%)</td></tr><tr><td>PPI left (kPa)</td><td>p&lt;0.05</td><td>-3 (-11%)</td><td>ns</td><td>-1.4%</td></tr></tbody></table>

Maximum of the recording

<table><caption>Table 4: Significance and difference between dynamic and static conditions (ns for not significant) for the average and the maximum of the recording, for the able-bodied and the wheelchair users. A positive difference means higher dynamic values.</caption><thead><tr><th rowspan="2">Parameters (units)</th><th colspan="2">Able-bodied</th><th colspan="2">Wheelchair users</th></tr><tr><th>Significance (p-value)</th><th>Difference unit (%)</th><th>Significance (p-value)</th><th>Significance (p-value)</th></tr></thead><tbody><tr><td>Shear force (N)</td><td>p&lt;0.001</td><td>+29 (+43%)</td><td>ns</td><td>+14 (+25%)</td></tr><tr><td>Normal force (N)</td><td>p&lt;0.001</td><td>-36 (-6%)</td><td>ns</td><td>+4 (+4%)</td></tr><tr><td>PPI right (kPa)</td><td>p&lt;0.05</td><td>-1 (-2%)</td><td>ns</td><td>0 (0%)</td></tr><tr><td>PPI left (kPa)</td><td>p&lt;0.05</td><td>-1 (-2%)</td><td>ns</td><td>1 (+5%)</td></tr></tbody></table>

<figure><img src="image_7.png" /><figcaption>Figure 5: Static, dynamic (average), and dynamic (maximum) values for PPI and shear force in both populations; in units of measurement at the top and percentage of static at the bottom.</figcaption></figure>
<table><caption>Table 5: Differences between able-bodied and wheelchair users in static conditions (average of the recording) (ns for not significant). A positive difference means higher values for wheelchair users.</caption><thead><tr><th rowspan="2">Parameters (units)</th><th colspan="2">Able-bodied</th><th colspan="2">Wheelchair users</th><th rowspan="2">Significance<br>Difference /<br>p-value</th></tr><tr><th>Mean (±1SD)</th><th>[Min-max]</th><th>Mean (±1SD)</th><th>[Min-max]</th></tr></thead><tbody><tr><td>Shear force (N)</td><td>72 (18)</td><td>[31-115]</td><td>65 (28)</td><td>[17-118]</td><td>-7 / ns</td></tr><tr><td>Normal force (N)</td><td>617 (167)</td><td>[306-1182]</td><td>778 (217)</td><td>[382-1109]</td><td>+160 /<br>p&lt;0.05</td></tr><tr><td>PPI right (kPa)</td><td>31 (8)</td><td>[14-53]</td><td>50 (13)</td><td>[21-72]</td><td>+19 / p&lt;0.05</td></tr><tr><td>PPI left (kPa)</td><td>31 (10)</td><td>[13-53]</td><td>46 (13)</td><td>[27-72]</td><td>+15 / p&lt;0.05</td></tr></tbody></table>
Average of the recording

<table><thead><tr><th rowspan="2">Parameters (units)</th><th colspan="2">Able-bodied</th><th colspan="2">Wheelchair users</th><th rowspan="2">Significance<br>Difference<br>Unit / p-value<br>(%) / p-value</th></tr><tr><th>Mean<br>(±1SD)</th><th>% of static</th><th>Mean<br>(±1SD)</th><th>% of static</th></tr></thead><tbody><tr><td>Shear force (N or %)</td><td>60 (19)</td><td>83</td><td>49 (28)</td><td>73</td><td>-11 / ns<br>-10% / ns</td></tr><tr><td>Normal force (N or %)</td><td>538 (154)</td><td>87</td><td>740 (153)</td><td>98</td><td>+202 / p&lt;0,05<br>+11% / p&lt;0,05</td></tr><tr><td>PPI right (kPa or %)</td><td>27 (8)</td><td>89</td><td>48 (12)</td><td>96</td><td>+21 / p&lt;0,001<br>+7% / p&lt;0,05</td></tr><tr><td>PPI left (kPa or %)</td><td>27 (10)</td><td>89</td><td>45 (12)</td><td>99</td><td>+18 / p&lt;0,001<br>+10% / p&lt;0,001</td></tr></tbody></table>

Maximum of the recording

<table><thead><tr><th rowspan="2">Parameters (units)</th><th colspan="2">Able-bodied</th><th colspan="2">Wheelchair users</th><th rowspan="2">Significance<br>Difference<br>Unit / p-value<br>(%) / p-value</th></tr><tr><th>Mean<br>(±1SD)</th><th>% of static</th><th>Mean<br>(±1SD)</th><th>% of static</th></tr></thead><tbody><tr><td>Shear force (N or %)</td><td>101 (33)</td><td>143</td><td>78 (32)</td><td>125</td><td>-22 / p&lt;0,05<br>-18% / ns</td></tr><tr><td>Normal force (N or %)</td><td>581 (167)</td><td>94</td><td>781 (154)</td><td>104</td><td>+200 / p&lt;0,001<br>+10% / p&lt;0,05</td></tr><tr><td>PPI right (kPa or %)</td><td>30 (8)</td><td>98</td><td>98 (13)</td><td>100</td><td>+68 / p&lt;0,001<br>+2% / p&lt;0,05</td></tr><tr><td>PPI left (kPa or %)</td><td>30 (10)</td><td>98</td><td>93 (12)</td><td>105</td><td>+63 / p&lt;0,001<br>+7% / ns</td></tr></tbody></table>

Range of variation of the recording (min-max)

<table><caption>Table 6: Difference between able-bodied and wheelchair users during the hand-cycling activity: average, maximum, and range of variation (minimum-maximum) of the recording in units and percentage of the static condition. A positive value for the difference implies greater force for wheelchair users (ns for non-significant).</caption><thead><tr><th rowspan="2">Parameters (units)</th><th colspan="2">Able-bodied</th><th colspan="2">Wheelchair users</th><th rowspan="2">Significance<br>Difference<br>Unit / p-value<br>(%) / p-value</th></tr><tr><th>Mean<br>(±1SD)</th><th>% of static</th><th>Mean<br>(±1SD)</th><th>% of static</th></tr></thead><tbody><tr><td>Shear force (N or %)</td><td>50 (29)</td><td>138</td><td>37 (14)</td><td>121</td><td>-13 / ns<br>-17% / ns</td></tr><tr><td>Normal force (N or %)</td><td>70 (43)</td><td>18</td><td>77 (29)</td><td>17</td><td>+8 / ns<br>-1% / ns</td></tr><tr><td>PPI right (kPa or %)</td><td>7 (8)</td><td>16</td><td>8 (11)</td><td>13</td><td>+18 / p&lt;0,001<br>-3% / p&lt;0,05</td></tr><tr><td>PPI left (kPa or %)</td><td>7 (6)</td><td>17</td><td>6 (5)</td><td>16</td><td>-1 / p&lt;0,001<br>-1% / p&lt;0,05</td></tr></tbody></table>
Supplementary online material

<table><caption>Table 7: Center of Pressure (barycenter of normal forces, calculated with the 52 sensors' matrix of the experimental seat [33]) and center of Tangential force (barycenter of shear forces, calculated with the 52 sensors' matrix of the experimental seat [33]) shift speed in m/s and area of displacement in cm² during the activity.</caption><thead><tr><th>Parameter (unit)</th><th>Mean (±1SD)</th><th>[Min-max]</th></tr></thead><tbody><tr><td>CoT speed (m/s)</td><td>1.08 (0.66)</td><td>[0.21-3.30]</td></tr><tr><td>CoP speed (m/s)</td><td>0.49 (0.35)</td><td>[0.08-1.61]</td></tr><tr><td>CoT circumscribed circle area (cm²)</td><td>8.54 (8.61)</td><td>[0,55-39,67]</td></tr><tr><td>CoP circumscribed circle area (cm²)</td><td>3.16 (3.77)</td><td>[0,10-23,82]</td></tr></tbody></table>

<figure><img src="image_8.png" /><figcaption>Figure 7: Linear relationship between the maximum anteroposterior displacement of the CoP and the magnitude of variation in shear force (between the average and the maximum value) on normalized data.</figcaption></figure>
References

[1] Kaye HS, Kang T, LaPlante MP. Mobility Device Use in the United States. 2000;

[2] Stucki ProfDr med. G. La cohorte de lésés médullaires InSCI [Internet]. Rennes, France; 2022. Available from: https://programme sofmer2022 com/session.php?action=planningDay&id=1000751.

[3] Le Fort M, Espagnacq M, Albert T, et al. Risk of pressure ulcers in tetraplegic people: a French survey crossing regional experience with a long-term follow-up. European Journal of Public Health. 2018;28:993-999.

[4] Consortium for Spinal Cord Medicine. Pressure Ulcer Prevention and Treatment Following Spinal Cord Injury: A Clinical Practice Guideline for Health-Care Professionals [Internet]. Second edition. Paralysed Veterans of America; 2014. Available from: https://www.mascip.co.uk/wp-content/uploads/2015/05/CPG_Pressure-Ulcer.pdf.

[5] Loerakker S. Aetiology of pressure ulcers. Eindhoven University of Technology (TU/E), Eindhoven. 2007;31.

[6] Sonenblum SE, Feng C, Sprigle S. The relationship between in-seat movement and pressure ulcers in wheelchair users with SCI/D. J Spinal Cord Med. 2022;1-9.

[7] Bader DL, Worsley PR. Technologies to monitor the health of loaded skin tissues. Biomed Eng Online. 2018;17:40.

[8] Goossens RHM. Fundamentals of Pressure, Shear and Friction and Their Effects on the Human Body at Supported Postures. In: Gefen A, editor. Bioengineering Research of Chronic Wounds: A Multidisciplinary Study Approach [Internet]. Berlin, Heidelberg: Springer; 2009 [cited 2020 Jun 3]. p. 1-30. Available from: https://doi.org/10.1007/978-3-642-00534-3_1.

[9] Gutierrez EM, Alm M, Hultling C, et al. Measuring seating pressure, area, and asymmetry in persons with spinal cord injury. Eur Spine J. 2004;13:374-379.

[10] Reenalda J, Jannink M, Nederhand M, et al. Clinical use of interface pressure to predict pressure ulcer development: a systematic review. Assist Technol. 2009;21:76-85.

[11] Stinson M, Porter A, Eakin P. Measuring Interface Pressure: A Laboratory-Based Investigation Into the Effects of Repositioning and Sitting. Am J Occup Ther. 2002;56:185-190.

[12] Andreoni G, Pedotti A, Ferrarin M. Pressure distribution on wheelchair cushions in static sitting and during manual propulsion. J Mech Med Biol. 2001;01:33-44.

[13] Paquin C, Rozaire J, Chenu O, et al. Studying mechanical load at body-seat interface during dynamic activities such as wheelchair propulsion: a scoping review. Disability and Rehabilitation: Assistive Technology. 2023;1-11.

[14] Tam EW, Mak AF, Lam WN, et al. Pelvic movement and interface pressure distribution during manual wheelchair propulsion. Archives of Physical Medicine and Rehabilitation. 2003;84:1466-1472.
[15] Hobson DA. Comparative effects of posture on pressure and shear at the body-seat interface. J Rehabil Res Dev. 1992;29:21-31.

[16] Redwood-Thomas J, Bowtell M, Graham S, et al. The Effect of Seating Setup on Shear Forces Experienced at the Seating Interface. Vancouver; 2020. p. 109.

[17] Aissaoui R, Kauffmann C, Dansereau J, et al. Analysis of pressure distribution at the body-seat interface in able-bodied and paraplegic subjects using a deformable active contour algorithm. Medical engineering & physics. 2001;23:359-367.

[18] Park J, Eberta SM, Reed MP, et al. Development of an Optimization Method for Locating the Pelvis in an Automobile Seat. Procedia Manufacturing. 2015;3:3738-3744.

[19] Sprigle S, Maurer C, Sonenblum SE. Load Redistribution in Variable Position Wheelchairs in People With Spinal Cord Injury. J Spinal Cord Med. 2010;33:58-64.

[20] Sprigle S, Wootten M, Sawacha Z, et al. Relationships Among Cushion Type, Backrest Height, Seated Posture, And Reach Of Wheelchair Users With Spinal Cord Injury. The Journal of Spinal Cord Medicine. 2003;26:236-243.

[21] Stinson M, Gillan C, Porter-Armstrong A. A Literature Review of Pressure Ulcer Prevention: Weight Shift Activity, Cost of Pressure Care and Role of the Occupational Therapist: British Journal of Occupational Therapy [Internet]. 2013 [cited 2020 Jun 17]; Available from: http://journals.sagepub.com/doi/10.4276/030802213X13651610908371.

[22] Maurer C, Sprigle S. Effect of Seat Inclination on Seated Pressures of Individuals With Spinal Cord Injury. Physical Therapy. 2004;84:255-261.

[23] Oomens, C.W.J., Bader, D.L., Loerakker, S., et al. Pressure induced deep tissue injury explained. Annals of Biomedical Engineering. 2015;43:297-305.

[24] Sonenblum SE, Sprigle S, Lopez RA. Manual Wheelchair Use: Bouts of Mobility in Everyday Life. Rehabilitation Research and Practice. 2012;2012:1-7.

[25] Dabnichki PA, Crocombe AD, Hughes SC. Deformation and Stress Analysis of Supported Buttock Contact. Proc Inst Mech Eng H. 1994;208:9-17.

[26] Kernozek TW, Lewin JE. Seat interface pressures of individuals with paraplegia: Influence of dynamic wheelchair locomotion compared with static seated measurements. Archives of Physical Medicine and Rehabilitation. 1998;79:313-316.

[27] Mendes PVB, Gradim LCC, Silva NS, et al. Pressure distribution analysis in three wheelchairs cushions of subjects with spinal cord injury. Disability and Rehabilitation: Assistive Technology. 2019;14:555-560.

[28] Sonenblum SE, Seol D, Sprigle SH, et al. Seated buttocks anatomy and its impact on biomechanical risk. J Tissue Viability. 2020;29:69-75.

[29] Sonenblum SE, Sprigle SH. Some people move it, move it... for pressure injury prevention. The Journal of Spinal Cord Medicine. 2018;41:106-110.
[30] Kraaijenbrink C, Vegter RJK, Hensen AHR, et al. Biomechanical and physiological differences between synchronous and asynchronous low intensity handcycling during practice-based learning in able-bodied men. Journal of NeuroEngineering and Rehabilitation. 2020;17:29.

[31] Wang X, Savonnet L, Theodorakos I, et al. Chapter 49 - Biomechanical human models for seating discomfort assessment. In: Scataglini S, Paul G, editors. DHM and Posturography [Internet]. Academic Press; 2019 [cited 2020 Sep 8]. p. 643–656. Available from: http://www.sciencedirect.com/science/article/pii/B9780128167137000490.

[32] Roberts TT, Leonard GR, Cepela DJ. Classifications In Brief: American Spinal Injury Association (ASIA) Impairment Scale. Clin Orthop Relat Res. 2017;475:1499–1504.

[33] Beurier G, Cardoso M, Wang X. A New Multi-Adjustable Experimental Seat for Investigating Biomechanical Factors of Sitting Discomfort [Internet]. Warrendale, PA: SAE International; 2017 [cited 2022 May 10]. Report No.: 2017-01-1393. Available from: https://www.sae.org/publications/technical-papers/content/2017-01-1393/.

[34] Kurtzke JF. Rating neurologic impairment in multiple sclerosis: an expanded disability status scale (EDSS). Neurology. 1983;33:1444–1452.

[35] Hollington J, Hillman SJ. Can static interface pressure mapping be used to rank pressure- redistributing cushions for active wheelchair users? Journal of Rehabilitation Research & Development. 2013;50:53–63.

[36] Cetisli Korkmaz N, Can Akman T, Kilavuz Oren G, et al. Trunk control: The essence for upper limb functionality in patients with multiple sclerosis. Multiple Sclerosis and Related Disorders. 2018;24:101–106.

[37] Gagnon D, Verrier M, Masani K, et al. Effects of Trunk Impairments on Manual Wheelchair Propulsion Among Individuals with a Spinal Cord Injury: A Brief Overview and Future Challenges. Topics in Spinal Cord Injury Rehabilitation. 2009;15:59–70.
<figure><img src="image_9.png" /><figcaption>Figure 1: Set-up with a participant and the hand crankset</figcaption></figure>

<figure><img src="image_10.png" /><figcaption>Figure 2: Experimental seat fitted with a wheelchair backrest. The Teximat® is placed on the seatpan in both conditions.</figcaption></figure>

<figure><img src="image_11.png" /><figcaption>Figure 3: Methodological figure: Illustration of the four time's parameters (maximum, minimum, average and range of variation). The signal is in blue.</figcaption></figure>
<table><caption>Table 1: Able-bodied and wheelchair users' characteristics</caption><thead><tr><th></th><th>Wheelchair users</th><th>N = 15</th><th>Able-bodied</th><th>N = 102</th><th>Differences</th></tr></thead><tbody><tr><td>Characteristics</td><td>Mean (±1SD)</td><td>[Min-max]</td><td>Mean (±1SD)</td><td>[Min-max]</td><td></td></tr><tr><td>Age (years)</td><td>40 (12)</td><td>[21-59]</td><td>36 (12)</td><td>[18-64]</td><td>ns</td></tr><tr><td>Sex (male/female)</td><td>16/1</td><td></td><td>55/47</td><td></td><td></td></tr><tr><td>Height (cm)</td><td>177 (8)</td><td>[155-187]</td><td>173 (9)</td><td>[155-191]</td><td>ns</td></tr><tr><td>Weight (kg)</td><td>81 (17)</td><td>[55-110]</td><td>75 (15)</td><td>[48-125]</td><td>p&lt;0,05</td></tr><tr><td>BMI (kg/m²)</td><td>26 (6)</td><td>[16-40]</td><td>24 (4)</td><td>[17-46]</td><td>ns</td></tr><tr><td>Neurological level of injury</td><td>C6-L2</td><td>C6-C8: 2<br>T1-T10: 9<br>T11-L2: 4</td><td></td><td></td><td></td></tr><tr><td>AIS grade</td><td>A: 7<br>B: 5<br>C: 1<br>D: 2</td><td></td><td></td><td></td><td></td></tr><tr><td>Aetiology Multiple sclerosis</td><td>1 (EDSS: 8)</td><td></td><td></td><td></td><td></td></tr><tr><td>Spinal cord injury</td><td>14</td><td></td><td></td><td></td><td></td></tr></tbody></table>

<table><caption>Table 2: Average and standard deviation of parameters in static conditions, for both able-bodied and wheelchair users.</caption><thead><tr><th>Parameters (units)</th><th>Average (±1SD)</th></tr></thead><tbody><tr><td>Shear force (N)</td><td>71 (19)</td></tr><tr><td>Normal force (N)</td><td>638 (183)</td></tr><tr><td>PPI right (kPa)</td><td>34 (12)</td></tr><tr><td>PPI left (kPa)</td><td>30 (12)</td></tr></tbody></table>
**Average of the recording**

<table><thead><tr><th>Parameters (units)</th><th>Average (±1SD)</th><th>% of static (±1SD)</th></tr></thead><tbody><tr><td>Shear force (N)</td><td>56 (23)</td><td>78 (24)</td></tr><tr><td>Normal force (N)</td><td>564 (167)</td><td>89 (9.9)</td></tr><tr><td>PPI right (kPa)</td><td>30 (12)</td><td>90 (12)</td></tr><tr><td>PPI left (kPa)</td><td>30 (12)</td><td>90 (11)</td></tr></tbody></table>

**Maximum of the recording**

<table><thead><tr><th>Parameters (units)</th><th>Average (±1SD)</th><th>% of static (±1SD)</th></tr></thead><tbody><tr><td>Shear force (N)</td><td>97 (35)</td><td>139 (41)</td></tr><tr><td>Normal force (N)</td><td>607 (178)</td><td>95 (10)</td></tr><tr><td>PPI right (kPa)</td><td>33 (12)</td><td>98 (11)</td></tr><tr><td>PPI left (kPa)</td><td>36 (12)</td><td>99 (10)</td></tr></tbody></table>

**Range of variation of the recording (min-max)**

<table><caption>Table 3: Average, maximum, and range of variation (min-max) of parameters during the activity in N or kPa and in % of the static condition, for both able-bodied and wheelchair users.</caption><thead><tr><th>Parameters (units)</th><th>Average (±1SD)</th><th>% of static (±1SD)</th></tr></thead><tbody><tr><td>Shear force (N)</td><td>90 (57)</td><td>136 (91)</td></tr><tr><td>Normal force (N)</td><td>113 (65)</td><td>18 (9)</td></tr><tr><td>PPI right (kPa)</td><td>8.31</td><td>23 (14)</td></tr><tr><td>PPI left (kPa)</td><td>7 (5)</td><td>23 (15)</td></tr></tbody></table>

<figure><img src="image_12.png" /><figcaption>Figure 4: Distribution of the range of variation as a function of the recording average</figcaption></figure>
Average of the recording

<table><thead><tr><th rowspan="2">Parameters (units)</th><th colspan="2">Able-bodied</th><th colspan="2">Wheelchair users</th></tr><tr><th>Significance (p-value)</th><th>Difference unit (%)</th><th>Significance (p-value)</th><th>Difference unit (%)</th></tr></thead><tbody><tr><td>Shear force (N)</td><td>p&lt;0.001</td><td>-15 (-17%)</td><td>p&lt;0.001</td><td>-21 (-27%)</td></tr><tr><td>Normal force (N)</td><td>p&lt;0.05</td><td>-79 (-13%)</td><td>ns</td><td>-35 (-2%)</td></tr><tr><td>PPI right (kPa)</td><td>p&lt;0.05</td><td>-3 (-11%)</td><td>ns</td><td>-1 (-4%)</td></tr><tr><td>PPI left (kPa)</td><td>p&lt;0.05</td><td>-3 (-11%)</td><td>ns</td><td>-1.4%</td></tr></tbody></table>

Maximum of the recording

<table><caption>Table 4: Significance and difference between dynamic and static conditions (ns for not significant) for the average and the maximum of the recording, for the able-bodied and the wheelchair users. A positive difference means higher dynamic values.</caption><thead><tr><th rowspan="2">Parameters (units)</th><th colspan="2">Able-bodied</th><th colspan="2">Wheelchair users</th></tr><tr><th>Significance (p-value)</th><th>Difference unit (%)</th><th>Significance (p-value)</th><th>Significance (p-value)</th></tr></thead><tbody><tr><td>Shear force (N)</td><td>p&lt;0.001</td><td>+29 (+43%)</td><td>ns</td><td>+14 (+25%)</td></tr><tr><td>Normal force (N)</td><td>p&lt;0.001</td><td>-36 (-6%)</td><td>ns</td><td>+4 (+4%)</td></tr><tr><td>PPI right (kPa)</td><td>p&lt;0.05</td><td>-1 (-2%)</td><td>ns</td><td>0 (0%)</td></tr><tr><td>PPI left (kPa)</td><td>p&lt;0.05</td><td>-1 (-2%)</td><td>ns</td><td>1 (+5%)</td></tr></tbody></table>

<figure><img src="image_13.png" /><figcaption>Figure 5: Static, dynamic (average), and dynamic (maximum) values for PPI and shear force in both populations; in units of measurement at the top and percentage of static at the bottom.</figcaption></figure>
<table><caption>Table 5: Differences between able-bodied and wheelchair users in static conditions (average of the recording) (ns for not significant). A positive difference means higher values for wheelchair users.</caption><thead><tr><th rowspan="2">Parameters (units)</th><th colspan="2">Able-bodied</th><th colspan="2">Wheelchair users</th><th rowspan="2">Significance<br>Difference /<br>p-value</th></tr><tr><th>Mean (±1SD)</th><th>[Min-max]</th><th>Mean (±1SD)</th><th>[Min-max]</th></tr></thead><tbody><tr><td>Shear force (N)</td><td>72 (18)</td><td>[31-115]</td><td>65 (28)</td><td>[17-118]</td><td>-7 / ns</td></tr><tr><td>Normal force (N)</td><td>617 (167)</td><td>[306-1182]</td><td>778 (217)</td><td>[382-1109]</td><td>+160 /<br>p&lt;0.05</td></tr><tr><td>PPI right (kPa)</td><td>31 (8)</td><td>[14-53]</td><td>50 (13)</td><td>[21-72]</td><td>+19 / p&lt;0.05</td></tr><tr><td>PPI left (kPa)</td><td>31 (10)</td><td>[13-53]</td><td>46 (13)</td><td>[27-72]</td><td>+15 / p&lt;0.05</td></tr></tbody></table>
Average of the recording

<table><thead><tr><th rowspan="2">Parameters (units)</th><th colspan="2">Able-bodied</th><th colspan="2">Wheelchair users</th><th rowspan="2">Significance<br/>Difference<br/>Unit / p-value<br/>(%) / p-value</th></tr><tr><th>Mean<br/>(±1SD)</th><th>% of static</th><th>Mean<br/>(±1SD)</th><th>% of static</th></tr></thead><tbody><tr><td>Shear force (N or %)</td><td>60 (19)</td><td>83</td><td>49 (28)</td><td>73</td><td>-11 / ns<br/>-10% / ns</td></tr><tr><td>Normal force (N or %)</td><td>538 (154)</td><td>87</td><td>740 (153)</td><td>98</td><td>+202 / p&lt;0,05<br/>+11% / p&lt;0,05</td></tr><tr><td>PPI right (kPa or %)</td><td>27 (8)</td><td>89</td><td>48 (12)</td><td>96</td><td>+21 / p&lt;0,001<br/>+7% / p&lt;0,05</td></tr><tr><td>PPI left (kPa or %)</td><td>27 (10)</td><td>89</td><td>45 (12)</td><td>99</td><td>+18 / p&lt;0,001<br/>+10% / p&lt;0,001</td></tr></tbody></table>

Maximum of the recording

<table><thead><tr><th rowspan="2">Parameters (units)</th><th colspan="2">Able-bodied</th><th colspan="2">Wheelchair users</th><th rowspan="2">Significance<br/>Difference<br/>Unit / p-value<br/>(%) / p-value</th></tr><tr><th>Mean<br/>(±1SD)</th><th>% of static</th><th>Mean<br/>(±1SD)</th><th>% of static</th></tr></thead><tbody><tr><td>Shear force (N or %)</td><td>101 (33)</td><td>143</td><td>78 (32)</td><td>125</td><td>-22 / p&lt;0,05<br/>-18% / ns</td></tr><tr><td>Normal force (N or %)</td><td>581 (167)</td><td>94</td><td>781 (154)</td><td>104</td><td>+200 / p&lt;0,001<br/>+10% / p&lt;0,05</td></tr><tr><td>PPI right (kPa or %)</td><td>30 (8)</td><td>98</td><td>98 (13)</td><td>100</td><td>+68 / p&lt;0,001<br/>+2% / p&lt;0,05</td></tr><tr><td>PPI left (kPa or %)</td><td>30 (10)</td><td>98</td><td>93 (12)</td><td>105</td><td>+63 / p&lt;0,001<br/>+7% / ns</td></tr></tbody></table>

Range of variation of the recording (min-max)

<table><caption>Table 6: Difference between able-bodied and wheelchair users during the hand-cycling activity: average, maximum, and range of variation (minimum-maximum) of the recording in units and percentage of the static condition. A positive value for the difference implies greater force for wheelchair users (ns for non-significant).</caption><thead><tr><th rowspan="2">Parameters (units)</th><th colspan="2">Able-bodied</th><th colspan="2">Wheelchair users</th><th rowspan="2">Significance<br/>Difference<br/>Unit / p-value<br/>(%) / p-value</th></tr><tr><th>Mean<br/>(±1SD)</th><th>% of static</th><th>Mean<br/>(±1SD)</th><th>% of static</th></tr></thead><tbody><tr><td>Shear force (N or %)</td><td>50 (29)</td><td>138</td><td>37 (14)</td><td>121</td><td>-13 / ns<br/>-17% / ns</td></tr><tr><td>Normal force (N or %)</td><td>70 (43)</td><td>18</td><td>77 (29)</td><td>17</td><td>+8 / ns<br/>-1% / ns</td></tr><tr><td>PPI right (kPa or %)</td><td>7 (8)</td><td>16</td><td>8 (11)</td><td>13</td><td>+18 / p&lt;0,001<br/>-3% / p&lt;0,05</td></tr><tr><td>PPI left (kPa or %)</td><td>7 (6)</td><td>17</td><td>6 (5)</td><td>16</td><td>-1 / p&lt;0,001<br/>-1% / p&lt;0,05</td></tr></tbody></table>
Supplementary online material

<table><caption>Table 7: Center of Pressure (barycenter of normal forces, calculated with the 52 sensors' matrix of the experimental seat [33]) and center of Tangential force (barycenter of shear forces, calculated with the 52 sensors' matrix of the experimental seat [33]) shift speed in m/s and area of displacement in cm² during the activity.</caption><thead><tr><th>Parameter (unit)</th><th>Mean (±1SD)</th><th>[Min-max]</th></tr></thead><tbody><tr><td>CoT speed (m/s)</td><td>1.08 (0.66)</td><td>[0.21-3.30]</td></tr><tr><td>CoP speed (m/s)</td><td>0.49 (0.35)</td><td>[0.08-1.61]</td></tr><tr><td>CoT circumscribed circle area (cm²)</td><td>8.54 (8.61)</td><td>[0,55-39,67]</td></tr><tr><td>CoP circumscribed circle area (cm²)</td><td>3.16 (3.77)</td><td>[0,10-23,82]</td></tr></tbody></table>

<figure><img src="image_14.png" /><figcaption>Figure 7: Linear relationship between the maximum anteroposterior displacement of the CoP and the magnitude of variation in shear force (between the average and the maximum value) on normalized data.</figcaption></figure>