# Biomechanical requirements of meat cutting tasks: a pilot study quantifying tasks sustainability and assistance required at the wrist

Divyaksh Subhash Chander, Aurélie Tomezzoli, Maria Pia Cavatorta, Mathieu Gréau, Stéphane Marie, Charles Pontonnier

► To cite this version:

Divyaksh Subhash Chander, Aurélie Tomezzoli, Maria Pia Cavatorta, Mathieu Gréau, Stéphane Marie, et al.. Biomechanical requirements of meat cutting tasks: a pilot study quantifying tasks sustainability and assistance required at the wrist. Applied Ergonomics, 2023, 116, pp.1-41. 10.1016/j.apergo.2023.104186. hal-04272926

HAL Id: hal-04272926

https://inria.hal.science/hal-04272926v1

Submitted on 7 Nov 2023

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons CC BY 4.0 - Attribution - International License
# Biomechanical requirements of meat cutting tasks: a pilot study quantifying tasks sustainability and assistance required at the wrist

Divyaksh Subhash Chander¹, Aurélie Tomezzoli¹, Maria Pia Cavatorta², Mathieu Gréau³, Stéphane Marie³, Charles Pontonnier¹*

1. Univ Rennes, CNRS, Inria, IRISA - UMR 6074, F-35000 Rennes, France

2. Politecnico di Torino, corso Duca degli Abruzzi, 24, 10129 Torino, Italy

3. Lab4i, Betton, France

* charles.pontonnier@inria.fr

## Abstract

The meat processing industry is particularly affected by distal upper limb musculoskeletal disorders.

This pilot study aims at proposing a methodology able to quantify biomechanical requirements of meat cutting tasks at butchers' dominant wrist and, when necessary, at estimating the assistance needed to reach sustainability. Six professional butchers repeatedly cut pieces of pork. Joint angles were recorded using a motion capture system, cutting forces using an instrumented knife.

Sustainability was computed by the maximal acceptable effort method. Assistance requirements were computed for isolated stressful exertions and for overall work cycle sustainability. Five butchers exceeded the sustainability threshold for wrist flexion. Ulnar or radial deviation torques were excessive for 2 and 3 of them, respectively. Extension torques were sustainable. The peak assistive torque for isolated exertions was at most 1.1Nm, 1.6Nm and 1.1Nm, and the percentage of assistance for overall sustainability was at most 60%, 56% and 56% for wrist flexion, ulnar and radial deviation, respectively.

## Keywords

wrist; occupational musculoskeletal disorders; muscle strength; range of motion, articular;

biomechanical specifications

## Highlights

- Meat cutting tasks exceeded sustainability threshold in wrist flexion

- Meat cutting tasks were sustainable in wrist extension
32

- Meat cutting tasks were sometimes not sustainable in ulnar or radial deviation

33

- Fast-paced nature of tasks affected subjects more than isolated stressful exertions

34

# 1. INTRODUCTION

35

36

Work-related Musculoskeletal Disorders (MSDs) are a major public health issue (de Kok et al., 2019).

37

38

39

40

41

42

The meat processing industry is one of the most affected industrial sectors, as MSDs prevalence is 10 to 15 times higher than in the general population (Lemerle & Chicot, 2018). Nordander et al. (2009) reported high prevalence of hand, wrist, and elbow MSDs among male meat cutters. Furthermore, Moore & Garg (1994) reported that hand and wrist MSDs prevailed (77%) over elbow MSDs (23%) among distal MSDs (n=104), in a pork processing facility employing 1100 individuals. Consequently, attempts to mitigate the risk of MSDs are suitable, especially at the distal upper limb.

43

44

45

46

47

48

49

50

51

52

53

54

55

56

57

58

Several risk factors for MSDs have been identified in the workplace, such as physical workload (e.g., high forces, repetition, awkward postures), organizational (e.g. task and job duration, recovery time), environmental (e.g., inappropriate lighting, low temperatures, noise), psychosocial (e.g., job demands, job content) and individual (e.g., individual skills, health problems) factors (Karasek et al., 1981; NF ISO 11228-3, 2007). Similarly, in the meat processing industry, several epidemiologic studies have found statistical links between the physical workload and MSDs incidence or prevalence (Frost et al., 1998; Moore & Garg, 1994; Nordander et al., 2009). Detailed ergonomics and biomechanical description of work organization and meat cutting tasks have been provided (Arvidsson et al., 2012; Silvin, 1999). Several studies attempted to understand the effect of work organization or knife sharpening in the meat cutting industry MSD issues (Karltun et al. 2016, Savescu et al. 2018). A number of studies focused on the effect of various additional parameters influencing risk factors e.g., the use of a hand tool like a knife (Claudon & Guiguet, 2003; Gorsche et al., 1998), the characteristics of the knife (Marsot et al., 2007; Tirloni et al., 2020), or the effect of the workbench height (Pontonnier et al., 2012). A recent study proposed in situ evaluation of physical risk factors (Villalobos & Mac Cawley, 2022). Attempts have been made to mitigate those risk factors: improved ergonomics of workstations (R. W. McGorry et al., 2004; Pontonnier et al., 2014), automation (Arvidsson et al., 2012; Tappin et al.,
2008). These attempts are still struggling to significantly enhance the work conditions, especially due to the industrial constraints that are still prevalent. To further reduce physical stress in meat cutting industry, exoskeletons or cobots (Maithani et al., 2021) delivering an assistive force to the user during the task execution can also be considered (Chander et al., 2022; Tomezzoli et al., 2023). However, such systems raise numerous issues, such as their control, the adaptability to the user, possible undesired effects (Pontonnier et al., 2021; Tomezzoli et al., 2023). Moreover, such systems may have to be designed with regard to the biomechanical requirements related to the task (Chander et al., 2022). According to Tirloni et al. 2021, the most recent measures of meat cutting forces using an instrumented knife are almost one decade old.

The use of a single aggregated indicator that globally reflects the biomechanical risk factors influencing the appearance of MSDs is interesting to assess the sustainability of a task and to forecast the effect of ergonomic interventions or assistive devices. Although analysis of specific risk factors like joint angles and torques are mandatory to understand in depth the biomechanical demand for a task, an aggregated indicator is also useful to specify the assistance requirements of an exoskeleton. The OCRA index (Occhipinti & Colombini, 2007), the Strain Index (Moore & Garg, 1995) and the TLV (ACGIH, 2016) are prominent methods to summarize the risk of MSDs for the upper limbs in repetitive tasks through one single indicator (NF ISO 11228-3, 2007). The current version of the TLV (ACGIH, 2016) relies on the maximal acceptable effort (MAE) model described by Potvin (2012), after refitting the model to enable higher maximal efforts for repetitive tasks occupying more than 50% of the work cycle (Abdel-Malek et al., 2020). The MAE is the maximal effort sustainable for tasks performed for 8 hours per day, determined experimentally through psychophysical studies. As the MAE method targeted fatigue phenomena at the distal upper limb, which is a frequent MSDs location in butchers (Nordander et al., 2009), this method is a good candidate to assess meat cutting tasks in terms of physical demand in this population. A mathematical relationship between the MAE and the duty cycle (DC), defined as the ratio of the task duration within a cycle to the work cycle time (CT), was proposed. Based on this relationship, the assistive torque required to reduce the effort to the level of MAE and
the rest required (RR) after a given task can be computed. For a work cycle consisting of multiple
tasks, the cumulative rest required can also be computed by summing up the RR for each task (Gibson
& Potvin, 2017). To the best of our knowledge, the MAE method has not been used in application to
meat cutting tasks before. The current study is an exploratory study aimed at evaluating the
biomechanical requirements of meat cutting tasks at professional butchers' dominant wrist, by the
cutting force, joint angles, joint torques, along with an estimation of the overall sustainability of the
task and, when needed, theoretical assistive torque required to reach sustainability using the MAE
model.

93

94

## 2. METHODS

95

### 2.1 Experiments

Six professional butchers, free from any musculoskeletal pain or discomfort in the last 6 months and
fully operational in the plant, participated in the experiments in a motion analysis laboratory. Three
pork pieces and one beef piece cutting tasks (Table 1) were selected by the partner meat processing
plant (COOPERL, France) regarding activities with frequent sick-leave disrupting the company. In this
work, only the pork trials were investigated due to limited beef trials, which had only two repetitions
each for two subjects. The study was approved by a national ethics committee (Comité Opérationnel
d'Evaluation des Risques Légaux et Ethiques, COERLE, n° 2021-07). Subjects signed an informed
consent form prior to participating in the experiment.

100

101

102

103

104

### 2.2 Equipment

Motion capture data was recorded at 200Hz using an optoelectronic system with 32 cameras (Qualisys Track Manager (QTM) 2021). 40 reflective markers were placed on the subject and 4 on the knife (Figure 1). Cutting force and moments were measured with a wireless instrumented knife (6 degrees of freedom (dof) force sensor, ATI Mini45-E Transducer, mounted between the handle and the replaceable blade, 500Hz). The partner meat processing plant supplied two blades with different
lengths of 11cm (shown in Figure 1; the figure shows the distance between the blade tip and the sensor reference frame and not the blade length) and 19.2cm that are typically used in the selected tasks. The subjects preferred the shorter blade for all pork trials and the longer blade for beef trials.

Forces and moment applied to the worktable, ground reaction forces and EMG signals of several upper limb muscles were recorded (not used in this study). All signals were synchronized with the motion capture system through the Transistor-Transistor logic (TTL) synchronization signal of the motion capture system. The joint strength at the wrist was measured using a Con-Trex MJ® isokinetic dynamometer (CMV AG, Dübendorf, Switzerland), following the constructor recommendation for isometric wrist strength assessment.

<table><caption>Table 1. Subject demographics and cutting trials performed.</caption><thead><tr><th></th><th>Sex</th><th>Height <sup>1</sup> (cm)</th><th>Age (years)</th><th>Weight <sup>1</sup> (kg)</th><th>Dominant Hand</th><th>Experience (years)</th><th>Piece cut</th><th>Repetitions</th></tr></thead><tbody><tr><td>S 1</td><td>M</td><td>172</td><td>50</td><td>82.2</td><td>Right</td><td>27</td><td>Pork belly side 1 (PB_1)</td><td>5</td></tr><tr><td>S 2</td><td>M</td><td>180</td><td>50</td><td>76.0</td><td>Right</td><td>21</td><td>Pork belly side 2 (PB_2)</td><td>5</td></tr><tr><td>S 3</td><td>M</td><td>178.5</td><td>47</td><td>86.1</td><td>Right</td><td>27</td><td>Pork spare rib (PSR)</td><td>5</td></tr><tr><td>S 4</td><td>M</td><td>176</td><td>40</td><td>78.4</td><td>Right</td><td>11</td><td>Pork spare rib (PSR)</td><td>5</td></tr><tr><td>S 5</td><td>M</td><td>172.5</td><td>48</td><td>53.6</td><td>Right</td><td>32</td><td>Pork Shoulder (PS) and Beef collar (BC)<sup>2</sup></td><td>5xPS then 2xBC<sup>2</sup></td></tr><tr><td>S 6</td><td>M</td><td>179.5</td><td>21</td><td>60.4</td><td>Right</td><td>5</td><td>Beef collar (BC)<sup>2</sup> and Pork Shoulder (PS)</td><td>2xBC<sup>2</sup> then 5xPS</td></tr></tbody></table>

120

121

122

<footnote n="1">¹Height and weight is with shoes. ²Not included in this study</footnote>
<figure><img src="image_2.png" /><figcaption>(a)</figcaption></figure>

123

124

<figure><img src="image_3.png" /><figcaption>(b)</figcaption></figure>

125

126

127

128

129

130

131

Figure 1: (a) Marker placement on the subject (markers on the right side are shown in orange, while those on the left side and centre are shown in blue). Additionally, markers located on the knife and table (one marker on the table was on the opposite and is not visible in the photo). The coordinate system on the knife shows the force sensor origin. (b) a subject in action during a pork belly cutting trial (left), and a maximal isometric wrist radial deviation strength test (right).

132

133
134

## 2.3 Protocol

135

136

137

138

139

140

141

142

143

After being briefed, the height and weight of the subject were recorded. Next, isometric maximal joint strength in wrist flexion (WF), wrist extension (WE), ulnar deviation (UD), and radial deviation (RD) of the dominant arm were measured with the dynamometer, in the posture recommended by the ergometer manufacturer (seated on the chair, strapped to fix shoulder, arm and trunk, shoulder at rest, elbow flexed at 90°, forearm pronated at 0° or 90° depending on the degree of freedom assessed, wrist at rest), for five seconds with verbal encouragements. The subject was then equipped with motion capture markers and EMG electrodes. They wore protective equipment (chainmail apron and sleeve for the non-dominant arm), markers located on the sternum, pelvis front left and right, non-dominant wrist and hand were placed on top of the protective equipment.

144

145

Next, a range-of-motion (ROM) trial was performed for geometrical calibration of the biomechanical model of the subject. The piece to be cut was placed on the table and weighed by the force sensor.

146

147

148

Then, the meat cutting trials were performed. To facilitate data processing, the subject marked the beginning and end of the cutting task by tapping the knife on the table. The knife was sharpened as and when deemed necessary by the subjects. Five repetitions were planned for each subject.

149

150

However, one repetition each from Subject 1 and Subject 2 could not be used due to technical issues during the recording of the motion capture data, with no data saved.

151

## 2.4 Data analysis

152

### 2.4.1 Inverse kinematics and dynamics analysis

153

154

155

156

157

158

Marker trajectories were processed in QTM and low pass filtered (4th order Butterworth with no phase shift at 10Hz). All force data was resampled to the mocap frequency. All trials were cropped to isolate the cutting task using the start and end taps in the cutting force. A biomechanical model of the upper limb (3 segments, 7 degrees of freedom), available in the motion analysis library CusToM (Muller et al., 2019), was used in this work. The model of the subject was scaled according to the height of the subject and the weight including the equipment (5.5 kg). The ROM trial was used for geometrical
calibration of the model (Puchaud et al., 2020). The knife force was applied to the hand of the subject after transformation into the global reference frame through the markers located on the knife. Wrist joint angles and joint torques were computed using CusToM. Further, the percentage durations of joint angles and joint torques between WF and WE, and UD and RD during the cycle were also computed. The grip of the knife was observed from the video recording of the trial.

## 2.4.2 Sustainability analysis

To perform the sustainability analysis, it was required to normalize the joint torques obtained from the inverse dynamics analysis to make them comparable to the MAE model. The normalized effort required by the subject for meat cutting was computed as the ratio of the joint torque required at the wrist to the joint (maximal) strength of the subject in the corresponding direction. The changes in the joint strength due to changes in joint angle and velocity were modeled by the torque-angle-velocity (TAV) envelopes for the wrist (Xia & Law, 2015). The envelopes were scaled by the ratio of the subject's isometric strength in the neutral posture to the strength from the TAV envelope at zero angle and velocity to obtain one TAV(q, ḋ) envelope per exertion type (WF, WE, RD and UD respectively), depending on the joint position q and velocity ḋ.

The cycle time (CT) for the trial performed by the subjects was computed as the duration between the starting and ending tap recorded by the subject. The largest CT from the repetitions performed by a subject was considered as the CT for the task. However, if the second largest CT was less than 75% of the largest CT, the repetition with the largest CT was excluded from the sustainability analysis as an outlier to possibly account for an unfamiliar laboratory environment and measuring equipment for the subjects. This affected one repetition each from Subject 1 and Subject 3. All individual cutting events (also called as exertions) in a given trial were defined by blocks of time with cutting force continuously greater than 5N. Duty Cycle (DCᵢ (%)) of an exertion i was computed as the ratio of the Time of Exertion TEᵢ to CT.
Since the peak effort lasted for a fraction of the duration of an exertion, often consisting of several cutting strokes, an equivalent effort (EqEffi) was computed as the peak of a bell curve of equivalent area under the curve (equal impulse) as that of the effort in the exertion i, during the same TEi. The joint torques issued from the inverse dynamics were processed the same way, resulting in equivalent joint torque per exertion (EqJTi).

The MAE i (%) for an exertion i was computed using the equation:

$$MAE_i = 1 - [DC_i - 1/28800]^{0.24} \quad (1)$$

28800 is the number of seconds in a standard 8-hour workday and implied that MAE = 100% for DC ≤ 1s/workday as defined in Potvin 2012.

The sustainability of each exertion was checked in isolation, for the four exertion directions at the wrist. If the EqEffi exceeded the MAEi for a given exertion, the exertion and work cycle were considered unsustainable. The assistive torque Tass1i needed to make the exertion i sustainable is denoted as Tass1 and was computed as the difference in percentage of EqEffi between EqEffi and MAEi, multiplied by the equivalent joint torque of exertion i EqJTi.

$$Tass1_i = \begin{cases} 0, & \text{if } EqEff_i \le MAE_i (EqEff_i - MAE_i) / EqEff_i * EqJT_i, \\ MAE_i (EqEff_i - MAE_i) / EqEff_i, & \text{if } EqEff_i > MAE_i \end{cases} \quad (2)$$

The rest required per exertion RRi was computed based on the TEi with the following equation (Gibson & Potvin, 2016):

$$RR_i = \frac{TE_i}{[1 - EqEff_i]^{4.167} + 1/28800} - TE_i \quad (3)$$

Despite each exertion being sustainable in isolation, a work cycle can be unsustainable due to a lack of adequate recovery period. The rest available in the work cycle, RAc(s), is computed as the difference between the CT and sum of the duration of all the n exertions of the cycle:
$$RA_c = CT - \sum_{i=1}^{n} TE_i \quad (4)$$

A work cycle was considered unsustainable if $RR_c$ (rest required per cycle, computed as the sum of the $RR_i$) exceeded $RA_c$. If the work cycle was unsustainable, the $EqEff$ of all the exertions were reduced by a constant percentage $\delta$ of their current value such that $RR_c$ was equal to $RA_c$. This percentage reduction was converted to assistive torque for each exertion $i$, denoted as $Tass2_i$, by multiplying $\delta$ by $Eq/T_i$.

$$Tass2_i = \begin{cases} 0, & \text{if } RR_c \le RA_c \delta * Eq/T_i, \\ 0, & \text{if } RR_c > RA_c \end{cases} \quad (5)$$

Naturally, a work cycle with at least an exertion with $EqEff_i$ greater than $MAE_i$ was unsustainable as $RR_c$ would exceed the $RA_c$. In such cases, computation of $\delta$ and $Tass2_i$ did not include $Tass1_i$.

In the results, the average of the maximum values of $Tass1_i$ and $Tass2_i$ considering all the exertions in the work cycle are presented for each subject. The above calculations for sustainability, i.e., $RR_c$, $Tass1$, and $Tass2$ were computed independently for each exertion direction at the wrist.

## 3. RESULTS

There were differences in the laboratory $CT$ for subjects performing the same task. However, the exertion frequencies were comparable for the subject pairs except for Subjects 3 (38.4 exertions per minute) and 4 (24.8 exertions per minute) (See Supplementary Material). The type of measurements, and subsequently of assistance are discussed. Wrist flexion angle exceeded the safety threshold of 45° (NF ISO 11228-3, 2007) for one subject, wrist extension for 5 subjects, ulnar deviation for 5 subjects and radial deviation for 3 subjects. Most of the work cycle was spent with the wrist flexed in ulnar deviation for cutting pork belly side (2 subjects), with wrist extended in radial deviation for cutting pork shoulder (2 subjects); both patterns were encountered for cutting pork spare rib (1 subject each) (Table 2). Peak resultant cutting force varied between 58 ± 7N and 105 ± 11N. Flexion joint torque was over-represented across time for every subject except Subject 4, irrespective of the flexion-extension
joint angle. Conversely, radio-ulnar deviation and torque directions seemed cross-coupled e.g.,
predominant radial torque being associated with predominant ulnar deviation (Table 2). Histograms
of joint torques and efforts as functions of joint angles displayed various profiles depending on tasks,
subjects and joint angles (see Figure 2C to F and Figure 3C to F for Subject 1; see supplementary
material for the other subjects).

Subjects 1 and 2 used a forward knife grip while Subjects 5 and 6 used predominantly the edge-in
reverse knife grip. Subjects 3 and 4 used both grips during the trial, with Subject 3 starting with the
forward knife grip and switching to the edge-in reverse knife grip midway through the trial. Instead,
Subject 4 started with the edge-out reverse knife grip, switched to forward knife grip, and finished
with edge-in reverse knife grip (Figure 4).

<table><caption>Table 2. Wrist postures and exertion: mean (+/- SD) of peak and average joint angle and joint torque values, and percentage of the work cycle that the subjects spent between different wrist postures and exertion directions</caption><thead><tr><th rowspan="3">Subject</th><th colspan="4">Joint Angle</th><th colspan="4">Joint Torque</th></tr><tr><th colspan="4">Peak value (°)</th><th colspan="4">Peak value (Nm)</th></tr><tr><th>Flexion</th><th>Extension</th><th>UD</th><th>RD</th><th>Flexion</th><th>Extension</th><th>UD</th><th>RD</th></tr></thead><tbody><tr><td>S1</td><td>45 (2)</td><td>-27 (3)</td><td>35<br>(1)</td><td>-9 (0)</td><td>7.9 (1.1)</td><td>-1.7 (0.7)</td><td>4.2<br>(3.1)</td><td>-6.2<br>(0.8)</td></tr><tr><td>S2</td><td>42 (3)</td><td>-45 (8)</td><td>41<br>(1)</td><td>-5 (2)</td><td>9.9 (1.2)</td><td>-1.2 (0.4)</td><td>3.4<br>(1.1)</td><td>-6.5<br>(1.3)</td></tr><tr><td>S3</td><td>41 (4)</td><td>-51 (2)</td><td>27<br>(3)</td><td>-8 (1)</td><td>8.0 (0.6)</td><td>-1.4 (0.3)</td><td>6.8<br>(0.6)</td><td>-8.5<br>(0.9)</td></tr><tr><td>S4</td><td>13 (11)</td><td>-57 (2)</td><td>26<br>(3)</td><td>-30<br>(1)</td><td>5.8 (1.4)</td><td>-3.0 (0.5)</td><td>5.5<br>(0.4)</td><td>-4.1<br>(1.1)</td></tr><tr><td>S5</td><td>39 (7)</td><td>-59 (2)</td><td>25<br>(2)</td><td>-18<br>(2)</td><td>9.6 (1.3)</td><td>-1.6 (1.2)</td><td>9.7<br>(0.7)</td><td>-1.3<br>(1.0)</td></tr><tr><td>S6</td><td>44 (7)</td><td>-64 (3)</td><td>20<br>(1)</td><td>-21<br>(1)</td><td>8.3 (1.2)</td><td>-5.1 (0.6)</td><td>8.4<br>(0.7)</td><td>-4.1<br>(1.0)</td></tr><tr><td></td><td colspan="4">Average value (°)</td><td colspan="4">Average value (Nm)</td></tr><tr><td>S1</td><td>22 (1)</td><td>-10 (2)</td><td>22<br>(1)</td><td>-6 (1)</td><td>2.8 (0.4)</td><td>-0.3 (0.1)</td><td>0.8<br>(0.2)</td><td>-1.7<br>(0.2)</td></tr><tr><td>S2</td><td>13 (2)</td><td>-10 (1)</td><td>23<br>(2)</td><td>-2 (1)</td><td>2.4 (0.2)</td><td>-0.3 (0.1)</td><td>0.8<br>(0.3)</td><td>-1.7<br>(0.2)</td></tr><tr><td>S3</td><td>23 (3)</td><td>-31 (3)</td><td>14<br>(1)</td><td>-3 (1)</td><td>2.7 (0.1)</td><td>-0.4 (0.1)</td><td>2.4<br>(0.1)</td><td>-3.2<br>(0.1)</td></tr><tr><td>S4</td><td>7 (7)</td><td>-30 (2)</td><td>15<br>(1)</td><td>-17<br>(1)</td><td>1.7 (0.3)</td><td>-0.7 (0.1)</td><td>1.9<br>(0.3)</td><td>-1.4<br>(0.3)</td></tr></tbody></table>
<table><thead><tr><th></th><th></th><th></th><th></th><th></th><th></th><th></th><th></th><th></th></tr></thead><tbody><tr><td>S5</td><td>17 (4)</td><td>-33 (2)</td><td>11<br>(2)</td><td>-8 (1)</td><td>3.0 (0.3)</td><td>-0.4 (0.3)</td><td>2.9<br>(0.1)</td><td>-0.3<br>(0.3)</td></tr><tr><td>S6</td><td>16 (3)</td><td>-26 (3)</td><td>9 (2)</td><td>-11<br>(1)</td><td>2.2 (0.2)</td><td>-1.2 (0.2)</td><td>2.3<br>(0.3)</td><td>-0.7<br>(0.1)</td></tr><tr><td></td><td></td><td></td><td>Duration (%)</td><td></td><td></td><td></td><td>Duration (%)</td><td></td></tr><tr><td>S1</td><td>84 (5)</td><td>16 (5)</td><td>96<br>(2)</td><td>4 (2)</td><td>94 (1)</td><td>6 (1)</td><td>16 (4)</td><td>84 (4)</td></tr><tr><td>S2</td><td>65 (6)</td><td>35 (6)</td><td>93<br>(2)</td><td>7 (2)</td><td>94 (3)</td><td>6 (3)</td><td>26 (6)</td><td>74 (6)</td></tr><tr><td>S3</td><td>62 (8)</td><td>38 (8)</td><td>83<br>(4)</td><td>17 (4)</td><td>92 (2)</td><td>8 (2)</td><td>36 (7)</td><td>64 (7)</td></tr><tr><td>S4</td><td>6 (6)</td><td>94 (6)</td><td>34<br>(5)</td><td>66 (5)</td><td>50 (5)</td><td>50 (5)</td><td>43 (6)</td><td>57 (6)</td></tr><tr><td>S5</td><td>29 (12)</td><td>71 (12)</td><td>34<br>(9)</td><td>66 (9)</td><td>93 (3)</td><td>7 (3)</td><td>90 (7)</td><td>10 (7)</td></tr><tr><td>S6</td><td>26 (3)</td><td>74 (3)</td><td>32<br>(4)</td><td>68 (4)</td><td>84 (5)</td><td>16 (5)</td><td>84 (2)</td><td>16 (2)</td></tr></tbody></table>

Yellow cells: joint angles > ergonomic thresholds, respectively 45°, 45°, 20° and 15° for flexion, extension, ulnar and radial

deviation (NF ISO 11228-3, 2007). UD: ulnar deviation. RD: radial deviation

237

238

239

240
<figure><img src="image_4.png" /></figure>

<figure><img src="image_5.png" /></figure>

<figure><img src="image_6.png" /></figure>

<figure><img src="image_7.png" /></figure>

<figure><img src="image_8.png" /></figure>

<figure><img src="image_9.png" /></figure>

241

242 Figure 2. Wrist flexion-extension for Subject 1: distribution of joint angles frequencies, and distribution

243 of cutting force, wrist flexion and extension torque and effort depending on wrist flexion and extension

244 angles
<figure><img src="image_10.png" /></figure>

<figure><img src="image_11.png" /></figure>

<figure><img src="image_12.png" /></figure>

<figure><img src="image_13.png" /></figure>

<figure><img src="image_14.png" /></figure>

<figure><img src="image_15.png" /></figure>

245

246

247

248

<caption>Figure 3. Wrist radio-ulnar deviation for Subject 1: distribution of joint angles frequencies, and distribution of cutting force, wrist radial and ulnar torque and effort depending on wrist radial and ulnar angles</caption>

249

250

251

252

253

254

Based on the sustainability analysis used in this study, the work cycle of only Subject 4 was sustainable in all exertion directions, as $RR_c$ was less than $RA_c$. For the remaining five subjects, $RR_c$ exceeded $RA_c$ in two exertion directions (Table 3). Wrist extension was the only direction for which $RR_c$ never exceeded $RA_c$. Subjects 1, 2 and 3 had $RR_c$ exceeding in radial deviation, while Subjects 5 and 6 had $RR_c$ exceeding in ulnar deviation.
<figure><img src="image_16.png" /><figcaption>Figure 4. Knife grips used during the experiments: a.) forward knife grip; b.) edge-in reverse knife grip (cutting edge inwards) ; c.) edge-out reverse knife grip (cutting edge outwards).</figcaption></figure>

Tass1 indicates if any exertion in the work cycle had EqEffᵢ that exceeded the MAEᵢ for its corresponding DCᵢ (Table 3). For three subjects (Subjects 3, 5 and 6), there was at least one and maximum three exertions where the EqEffᵢ that exceeded the MAEᵢ, on a total of 27 exertions per cycle on average (See Supplementary Material). The mean of the peak assistive torque required to reduce the EqEffᵢ to MAEᵢ across the repetitions of the subjects was at most 1.6Nm. Naturally, subjects requiring Tass1 required Tass2 as well to make the work cycle sustainable in the corresponding exertion directions. 50% (1.1Nm) reduction in wrist flexion effort (torque) was needed for Subject 5. While 56% (5.6Nm) reduction in ulnar and radial deviation effort (torque) was needed for Subject 5 and 3, respectively.

The work cycle can be unsustainable even if individual exertions are sustainable as seen in the case of Subjects 1 and 2 performing PB. They do not require Tass1 but require up to 60% (5.8Nm) reduction in wrist flexion effort (torque) and up to 40% (2.2Nm) reduction in radial deviation effort (torque) to make the work cycle sustainable. Subjects 3 and 6 also required Tass2 in wrist flexion while not requiring Tass1. In wrist extension, Subject 6 required Tass2 in only one repetition, resulting in mean RRc lower than RAc. Likewise, in ulnar deviation Subjects 2 and 3 required Tass2 in one and two repetitions, respectively, resulting in mean RRc lower than RAc. Table 3
<table><caption>Table 3. Rest available in the work cycle $RA_c$, rest required $RR_c$, assistive torques $τ$ required computed in $Tass1$ (T1) and $Tass2$ (T2) (Nm), decrease $δ$ in current effort value required computed in $Tass2$ (%): individual results, mean $μ$ and standard deviation (SD)</caption><thead><tr><th rowspan="2"></th><th rowspan="2">(s)</th><th colspan="4">Flexion</th><th colspan="4">Extension</th><th colspan="4">Ulnar Deviation</th><th colspan="4">Radial Deviation</th></tr><tr><th>(s)</th><th>(N m)</th><th>(N m)</th><th>(%)</th><th>(s)</th><th>(N m)</th><th>(N m)</th><th>(%)</th><th>(s)</th><th>(N m)</th><th>(N m)</th><th>(%)</th><th>(s)</th><th>(N m)</th><th>(N m)</th><th>(%)</th></tr></thead><tbody><tr><td>S 1</td><td>22</td><td>10 8</td><td>0.0</td><td>4.2</td><td>56</td><td>1</td><td>0.0</td><td>0.0</td><td>0</td><td>3</td><td>0.0</td><td>0.0</td><td>0</td><td>56</td><td>0.0</td><td>2.2</td><td>40</td></tr><tr><td>S D</td><td>3</td><td>39</td><td>0.0</td><td>1.3</td><td>13</td><td>1</td><td>0.0</td><td>0.0</td><td>0</td><td>1</td><td>0.0</td><td>0.0</td><td>0</td><td>6</td><td>0.0</td><td>0.4</td><td>10</td></tr><tr><td>S 2</td><td>25</td><td>13 6</td><td>0.0</td><td>5.8</td><td>60</td><td>0</td><td>0.0</td><td>0.0</td><td>0</td><td>14</td><td>0.0</td><td>0.2</td><td>3</td><td>57</td><td>0.0</td><td>2.1</td><td>37</td></tr><tr><td>S D</td><td>6</td><td>39</td><td>0.0</td><td>1.6</td><td>12</td><td>0</td><td>0.0</td><td>0.0</td><td>0</td><td>13</td><td>0.0</td><td>0.4</td><td>7</td><td>18</td><td>0.0</td><td>1.5</td><td>22</td></tr><tr><td>S 3</td><td>8</td><td>26</td><td>0.0</td><td>4.0</td><td>47</td><td>0</td><td>0.0</td><td>0.0</td><td>0</td><td>8</td><td>0.0</td><td>0.4</td><td>5</td><td>63</td><td>1.1</td><td>5.6</td><td>56</td></tr><tr><td>S D</td><td>1</td><td>4</td><td>0.0</td><td>1.0</td><td>10</td><td>0</td><td>0.0</td><td>0.0</td><td>0</td><td>1</td><td>0.0</td><td>0.5</td><td>6</td><td>17</td><td>0.7</td><td>1.0</td><td>7</td></tr><tr><td>S 4</td><td>17</td><td>5</td><td>0.0</td><td>0.0</td><td>0</td><td>6</td><td>0.0</td><td>0.0</td><td>0</td><td>9</td><td>0.0</td><td>0.0</td><td>0</td><td>6</td><td>0.0</td><td>0.0</td><td>0</td></tr><tr><td>S D</td><td>2</td><td>1</td><td>0.0</td><td>0.0</td><td>0</td><td>1</td><td>0.0</td><td>0.0</td><td>0</td><td>1</td><td>0.0</td><td>0.0</td><td>0</td><td>2</td><td>0.0</td><td>0.0</td><td>0</td></tr><tr><td>S 5</td><td>30</td><td>32 1</td><td>1.1</td><td>5.4</td><td>50</td><td>3</td><td>0.0</td><td>0.0</td><td>0</td><td>44 1</td><td>1.6</td><td>5.6</td><td>56</td><td>3</td><td>0.0</td><td>0.0</td><td>0</td></tr><tr><td>S D</td><td>4</td><td>22 5</td><td>0.9</td><td>1.4</td><td>9</td><td>6</td><td>0.0</td><td>0.0</td><td>0</td><td>10 5</td><td>0.4</td><td>0.3</td><td>6</td><td>5</td><td>0.0</td><td>0.0</td><td>0</td></tr></tbody></table>
<table><tbody><tr><td>S<br>6</td><td>40</td><td>12<br>7</td><td>0.0</td><td>3.1</td><td>36</td><td>30</td><td>0.0</td><td>0.1</td><td>2</td><td>55<br>9</td><td>0.7</td><td>5.0</td><td>53</td><td>7</td><td>0.0</td><td>0.0</td><td>0</td></tr><tr><td>S<br>D</td><td>4</td><td>40</td><td>0.0</td><td>1.2</td><td>10</td><td>16</td><td>0.0</td><td>0.2</td><td>4</td><td>19<br>6</td><td>0.5</td><td>0.7</td><td>7</td><td>4</td><td>0.0</td><td>0.0</td><td>0</td></tr></tbody></table>

279

Yellow cells: assistance required.

280

## 4. DISCUSSION

281

The aim of this exploratory study was to propose an extensive biomechanical characterization of meat cutting tasks performed by a reduced set of professional butchers, to estimate the need for assistance and, when required, to provide data on the direction and level of assistance needed at the wrist. The global assessment of the tasks showed that every professional butcher but one exceeded the biomechanical sustainability threshold described by Potvin (2012) and Gibson & Potvin (2016).

282

283

284

285

286

287

288

289

290

291

292

293

294

295

296

297

298

Comprehensive kinematic and kinetic data with professional butchers performing real meat cutting tasks were collected for this study. Joint angle values often exceeded recommendations (NF ISO 11228-3, 2007), especially in wrist extension (45°) and ulnar deviation (20°). Capturing the kinematics of the knife was also critical to understand the difference in knife grips and its consequences for the joint torques required at the wrist. For example, this study showed that for PSR, Subject 4 had a sustainable work cycle while Subject 3 had an unsustainable work cycle. This can be due to the specific strategy of Subject 4. Subject 4 used three different knife grips enabling him to obtain a fairly even split in duration of exertion between the exertion directions, unlike Subject 3, who used two knife grips. Moreover, the additional change in knife grip for Subject 4 resulted in greater *CT* and *RA*<sub>c</sub> compared to Subject 3, leading to a lower frequency of exertions in the work cycle. These factors favorably affected the sustainability analysis for Subject 4. Given the limited subjects in this study, a future study with more subjects should investigate in detail if switching knife grips could be a viable strategy to reduce the risk of MSDs.

299

Raw value of forces also exceeded recommendations stated in the RULA ergonomics tool assessment (McAtamney & Nigel Corlett, 1993), as peak and average forces always exceeded the first threshold

300
of 20N for repeated loads and for Subject 2, the peak force exceeded the second threshold (100N).
This is consistent with epidemiological studies that display correlations between physical load and
MSDs incidence or prevalence in the meat cutting industry (Frost et al., 1998; Gorsche et al., 1998;
Moore & Garg, 1994; Nordander et al., 2009). In addition, peak and average cutting moments of
16.2Nm and 4.0Nm, respectively, have been reported for pork shoulder deboning tasks (Dempsey &
McGorry, 2004). The cutting moments at the handle core approximately translated into peak and
average cutting force of 75N and 19N, respectively, considering blade length of 15cm and half handle
length of 6.5cm (Dempsey & McGorry, 2004; R. W. McGorry, 2001). These values compare well with
the values reported in the current study. The consistency of epidemiological and biomechanical
literature with our study legitimates the use of assistance to reduce the physical workload, though the
number of tasks and subjects investigated was low in our study. Thus, the direction, then the level of
assistance that could be proposed based on our results will be discussed consecutively.

## 4.1 Directions to be assisted

In our study, wrist flexion torques were excessive compared to subject individual capabilities for
almost every subject, ulnar deviation or radial deviation torques were excessive depending on
subjects, and extension torques were considered sustainable for every subject. The differences in
torque and assistance requirement between radio-ulnar deviation can be associated with changes in
cutting strategy or knife grip for different tasks. PB, performed by Subjects 1 and 2 with the forward
knife grip, were over-represented in radial deviation while PS, performed by Subjects 5 and 6 with
predominantly the edge-in reverse knife grip, were over-represented in ulnar deviation. Thus, our
results suggest that assistive devices must be able to adjust to task and/or subject specific
requirements to be efficient. In addition, high inter-subject (or inter-task) variability was found for
every parameter measured or computed in our study, which was expected in meat cutting tasks
(Chander et al., 2022; Dempsey & McGorry, 2004; Silvin, 1999). Moreover, only three tasks were
investigated in the study, while a range of different tasks is usually performed in a meat processing
326

plant, and each task was performed by two subjects specialized in this specific task. To further evaluate

327

the results of the study, the consistency of our data with the MSDs encountered in the meat cutting

328

industry are discussed.

329

The epidemiologic literature highlights carpal tunnel syndrome, trigger finger syndromes (Frost et al.,

330

1998; Gorsche et al., 1998) and non-specific hand/wrist pain (Moore & Garg, 1994) as the most

331

prevalent distal upper limb MSDs in the meat cutting industry. Forceful exertions, especially when

332

combined with repetitive movement or awkward posture of hand or fingers, are considered a risk

333

factor for carpal tunnel syndrome (Keir et al., 2021). Trigger finger syndromes are due to finger flexor

334

tendons tenosynovitis (Durand et al., 2011), finger flexors being involved both in fingers and wrist

335

flexion (Marieb, 1993). Consequently, the excessive wrist flexion exertions highlighted in our study

336

seem consistent with the high prevalence of carpal tunnel and trigger finger syndromes in butchers,

337

although such results should be confirmed on a larger cohort of subjects. Also, the sustainable

338

exertions in wrist extension highlighted in our study seems consistent with the epidemiologic

339

literature, as e.g. finger extensors MSDs are not highlighted in epidemiologic studies performed in the

340

meat processing industry (Frost et al., 1998; Gorsche et al., 1998; Moore & Garg, 1994). Elbow

341

tendonitis are common among butchers (Moore & Garg, 1994), but no details about the medial versus

342

radial elbow tendonitis were found in the literature. Additionally, radial and ulnar deviations are both

343

controlled by several muscles, inserted on both lateral and medial epicondylitis, like finger extensors

344

and flexor carpi radialis for radial deviation and flexor and extensor carpi ulnaris for ulnar deviation.

345

Thus, literature does not give indication regarding the relative importance of a radial or ulnar deviation

346

torque assistance and cannot help prioritizing between assistance for radial or ulnar deviation.

347

Consequently, wrist flexion and possibly radio-ulnar deviation seem the more relevant directions to

348

be assisted during meat cutting tasks. As overrepresentation across time of wrist flexion was always

349

associated with overrepresented ulnar deviation, and wrist extension with radial deviation, a coupled

350

functional motion can be suspected. This coupled motion, known as a "dart-throwing motion" of the
wrist, has been demonstrated to be the most common wrist motion in activities of daily living (Moritomo et al., 2007). This raises the question of the need to assist the wrist proportionally in coupled degrees of freedom. In addition, maximal torques were developed in different wrist positions, depending on the subject (see Figure 2A and Figure 3A for Subject 1). Consequently, assistance should be provided on the largest possible articular amplitude in flexion/extension.

## 4.2 Level of assistance

Assistive torque requirements were computed in two ways. *Tass1* (Table 3) identified exertions that were highly stressful due to large effort requirement for the *DC*<sub>i</sub> of the exertion. *RR*<sub>c</sub> and *Tass2* (Table 3) served to understand the overall sustainability of the work cycle. Meat cutting is a highly dynamic activity with cutting exertions often consisting of several cutting strokes, resulting in peaks and dips in the computed effort. The sustainability analysis showed more instances of *Tass2* requirement than *Tass1* requirement, indicating that the fast-paced and repetitive nature of meat cutting tasks is a problem that affected subjects more than isolated exertions with large force/torque requirements. There can be several ways to address the problem. With *Tass2*, we adapted a strategy of uniform reduction in the effort required in the work cycle to achieve sustainability while maintaining the same cycle time. With *Tass1*, we targeted specific exertions and made them sustainable in isolation, without considering the sustainability of the overall cycle, which explains why *Tass1* is much lower than *Tass2*. *Tass1* and *Tass2* can potentially be used to determine the specifications of an assistive device, however the data must be extended with more subjects. While Subjects 1 and 2, performing PB, showed similar reduction in effort in the corresponding exertion directions, subject pairs for PSR and PS showed some inconsistencies in the level of assistance required.

*TAV* envelopes (Xia & Law, 2015) were implemented in the *MAE* models, defining the joint strengths. The *MAE* model accounted more or less for torques, repetitiveness, joint angles, and velocity in a single indicator, the three first factors being major factors of MSDs (NF ISO 11228-3, 2007). The choice
in this study was to measure isometric joint strengths, making *TAV* envelopes specific instead of using some of the literature. It was indeed expected that butchers will be stronger in wrist strength compared to literature data. This was true for all but Subjects 5 and 6 in radial deviation strength (Chander et al., 2022; Xia & Law, 2015). Thus, the results in this study must be carefully considered when applying to new butchers, whose wrist strength may not still be conditioned by their work.

McGorry et al. (2000) found that experienced butchers spent less time applying torque than less experienced butchers and suggested that using more power and less time allowed experienced butchers a greater recovery period or conditioning at job allowed them to sustain higher exertion levels than less experienced butchers. Based on the *MAE* model, sustainability can be achieved by reducing effort or increasing recovery period, or a combination of both. It is also certain that an increase in joint strength of experienced butchers due to job conditioning will reduce the effort exerted in all the exertions and, consequently, result in a reduction in RR for the task. Moreover, as seen in this study, change of knife grip during meat cutting tasks might also be a strategy that could be employed to improve the sustainability of the task. The *MAE* model, with subject specific joint strength, can indeed be used to investigate the strategies used by experienced butchers in a future study.

However, joint strength implemented in *MAE* models are only estimations, as many factors are known to modify them (Nuzzo et al., 2019). For example, neither the influence of interactions between the different degrees of freedom on wrist joint strength (La Delfa & Potvin, 2017), nor the influence of remote joint angles like elbow and shoulder (Delp et al., 1996; Xia & Law, 2015, Haering et al. 2017) could be estimated by available models. Both issues are encountered in the tasks, as flexion-extension and radio-ulnar deviations are performed during meat cutting, i.e. with or without shoulder abduction.

Additionally, joint torques estimated are net joint torques. Thus, muscle co-contraction is not accounted for during the tasks, even if co-contraction is necessary to ensure a given level of performance during the execution of the task. This is an approximation (Latash, 2018), which can underestimate the assessment of MSDs risk. On the opposite, we also assumed that the muscles were
402 activated to provide an exertion torque in a given direction. However, the same joint torque can be
403 provided by different muscles over time, with adaptive changes in muscle recruitment patterns in case
404 of fatigue (Blangsted et al., 2005) in real working conditions. Thus, RR<sub>c</sub> might be overestimated in our
405 study. These two conflicting issues may ask for further analyses at the muscle level e.g. by EMG, to
406 gain an in-depth understanding of the motor adaptations associated with performing meat cutting
407 tasks over a long period of time and better assess their sustainability.

408

409

410

411 **4.3 Limitations**

412 Limitations due to the low number of subjects involved in the study and assistive torque computation
413 have been previously discussed. Nevertheless, we can emphasize that the individual differences
414 associated with this small cohort may have a significant effect on the results, particularly as a result of
415 the healthy worker effect (Li and Sung, 1999). Limitations due to the conditions of measurement also
416 exist. The study was performed in a laboratory, where working conditions substantially differ from
417 those encountered in industry. For example, butchers usually work in a cold, noisy environment at a
418 sustained pace (Silvin, 1999), all these factors being identified as risk factors for MSDs (NF ISO 11228-
419 3, 2007). Conversely, specific constraints exist in a laboratory, like extra equipment and procedures
420 for data collection. Furthermore, our study focused on exertions at the wrist, as distal MSDs are the
421 most common (Nordander et al., 2009), but assessment of other exertions could also be of interest.
422 For example, using a hand tool like a knife involves finger flexors exertion (Marieb, 1993) and is a
423 known risk factor for MSDs in butchers (Claudon & Guiguet, 2003; Gorsche et al., 1998).
424 Measurements related to the gripping force (Gorsche et al., 1998) might be of interest, though
425 technical possibilities of assisting gripping do not seem easy to implement (Mayer et al. 2022), due to
426 the changes in knife gripping type in a single meat cutting task (Claudon & Guiguet, 2003). The physical
427 workload at the shoulder should also be assessed while evaluating an assisting device, as MSDs are
428 also common at shoulder (Nordander et al., 2009). More generally, MSDs are multifactorial diseases
429 (Bernard et al., 1997; Gouvernement du Canada, 2022; NF ISO 11228-3, 2007). In consequence, the
430 assistance of joint torques must be mixed with other factors to be acceptable as an ergonomic
431 approach.

432 Finally, sustainability thresholds should be considered with caution. It has to be noticed that the *MAE*
433 method, specifically developed to characterize the onset of upper limb fatigue (Potvin, 2012), is only
434 one of the various methods for globally assessing the physical risks of MSDs appearance. The choice
435 among these methods has been proven to influence the risk level estimation in some situations
436 (Antonucci, 2019). This choice is still in discussion within the scientific community (ACGIH, 2016;
437 Moore & Garg, 1995; Occhipinti & Colombini, 2007). However, in a recent study challenging different
438 criteria for rest requirement assessment, this model was found to require shorter duty cycle times and
439 lighter loads to be sustainable (Neumann et al., 2020).

440 5. CONCLUSION

441 This work proposed an extensive characterization of biomechanical requirements for a reduced set of
442 professional butchers, and computed the sustainability and assistive torque requirements in case of
443 the potential use of an exoskeleton at the wrist. Five of six subjects in this study exerted predominantly
444 in wrist flexion, resulting in an unsustainable workload. The exertions in radio-ulnar deviations
445 depended on the task and possibly on knife grip used by the subjects. Peak assistive torque values
446 were around 5.6 - 5.8Nm in wrist flexion, ulnar deviation, and radial deviation. However, an ideal
447 exoskeleton design should enable adjustable assistance to suit the requirements of different tasks,
448 even if practical issues may enforce the design to be focused on the most unsustainable subtasks to
449 be efficient on the largest population. The sustainability analysis showed that the fast pace of the meat
450 cutting tasks affected subjects more than isolated stressful exertions. Future work should extend the
451 sustainability analysis to more subjects and tasks, potentially also investigating subject-specific
452 strategies for the same task. In addition, the other degrees of freedom of the upper limb recorded
453 during this experimentation should be investigated in a similar manner to give a more complete view
454 of the biomechanical requirements of meat cutting.

455 ACKNOWLEDGMENTS

456 This study has been funded by the Région Bretagne, within the frame of the EXOSCARNE 2.0 project,
457 and supported by French government funding managed by the National Research Agency under the
458 Investments for the Future program (PIA) with the grant ANR-21-ESRE-0030 (CONTINUUM project).
459 The authors thank COOPERL company workers for their participation, and the LAB4i company for their
460 support during the experimentation.

461

462 REFERENCES

463 Abdel-Malek, D. M., Foley, R. C. A., Wakeely, F., Graham, J. D., & La Delfa, N. J. (2020). Exploring
464 Localized Muscle Fatigue Responses at Current Upper-Extremity Ergonomics Threshold Limit
465 Values. *Human Factors*, 18720820940536.

466 ACGIH. (2016). Upper limb localized fatigue : TLV® physical agents7th edition documentation. *The*
467 American Conference of Governmental Industrial Hygienists.

468 Antonucci, A. (2019). Comparative analysis of three methods of risk assessment for repetitive
469 movements of the upper limbs : OCRA index, ACGIH(TLV), and strain index. *International*
470 *Journal of Industrial Ergonomics*, 70, 9-21.

471 Arvidsson, I., Balogh, I., Hansson, G.-Å., Ohlsson, K., Akesson, I., & Nordander, C. (2012).
472 Rationalization in meat cutting—Consequences on physical workload. *Applied Ergonomics*,
473 43(6), 1026-1032.
474

Bernard, B. P., Putz-Anderson, V., & Burt, S. (1997). *Musculoskeletal disorders and workplace factors : A critical review of epidemiologic evidence for work-related musculoskeletal disorders of the neck, upper extremity, and low back.*

475

476

477

Blangsted, A. K., Sjøgaard, G., Madeleine, P., Olsen, H. B., & Søgaard, K. (2005). Voluntary low-force contraction elicits prolonged low-frequency fatigue and changes in surface electromyography and mechanomyography. *Journal of Electromyography and Kinesiology: Official Journal of the International Society of Electrophysiological Kinesiology*, 15(2), 138-148.

478

479

480

481

Chander, D. S., Marie, S., Gréau, M., & Pontonnier, C. (2022). Biomechanical requirements of meat cutting tasks: An overview. *Comput. Methods Biomech. Biomed. Eng.*, 25(S1), 1-3.

482

483

Claudon, L., & Guiguet, C. (2003). Analyse de la tenue en main des couteaux lors d'opérations de désossement dans différents secteurs de la filière viande. *Le travail humain*, 66(4), 377-390.

484

485

de Kok, J., Vroonhof, P., Snijders, J., Roullis, G., Clarke, M., Peereboom, K., van Dorst, P., & Isusi, I. (2019). *Work-related musculoskeletal disorders: Prevalence, costs and demographics in the EU / Safety and health at work EU-OSHA*. European Agency for Safety and Health at Work (EU-OSHA). https://osha.europa.eu/fr/publications/work-related-musculoskeletal-disorders-prevalence-costs-and-demographics-eu/view

486

487

488

489

490

Delp, S. L., Grierson, A. E., & Buchanan, T. S. (1996). Maximum isometric moments generated by the wrist muscles in flexion-extension and radial-ulnar deviation. *Journal of Biomechanics*, 29(10), 1371-1375.

491

492

493

Dempsey, P. G., & McGorry, R. W. (2004). Investigation of a Pork Shoulder Deboning Operation. *Journal of Occupational and Environmental Hygiene*, 1(3), 167-172.

494

495

Durand, S., Daunois, O., Gaujoux, G., Méo, S., Sassoon, D., & Strubé, F. (2011). [Trigger digits]. *Chirurgie De La Main*, 30(1), 1-10.

496

497

Frost, P., Andersen, J. H., & Nielsen, V. K. (1998). Occurrence of carpal tunnel syndrome among slaughterhouse workers. *Scandinavian Journal of Work, Environment & Health*, 24(4), 285-292.

498

499
Gibson, M., & Potvin, J. R. (2016, October). An equation to calculate the recommended cumulative rest allowance across multiple subtasks. In *Association of Canadian Ergonomists (ACE) Conference, Niagara Falls, ON*.

Gibson, M., & Potvin, J. (2017). *Calculating the Maximum Acceptable Effort for an Isolated Subtask While Still Accounting for the Demands of all Other Subtasks*.

Haering, D., Pontonnier, C., Bideau, N., Nicolas, G., & Dumont, G. (2019). Using Torque-Angle and Torque-Velocity Models to Characterize Elbow Mechanical Function: Modeling and Applied Aspects. *Journal of Biomechanical Engineering, 141*(8).

Gorsche, R., Wiley, J. P., Renger, R., Brant, R., Gemer, T. Y., & Sasyniuk, T. M. (1998). Prevalence and incidence of stenosing flexor tenosynovitis (trigger finger) in a meat-packing plant. *Journal of Occupational and Environmental Medicine, 40*(6), 556-560.

Gouvernement du Canada, C. canadien d'hygiène et de sécurité au travail. (2022, février 1). *Troubles musculo-squelettiques liés au travail - Facteurs de risque : Réponses SST*. https://www.cchst.ca/oshanswers/ergonomics/risk.html

Karasek, R., Baker, D., Marxer, F., Ahlbom, A., & Theorell, T. (1981). Job decision latitude, job demands, and cardiovascular disease : A prospective study of Swedish men. *American Journal of Public Health, 71*(7), 694-705.

Karltun, J., Vogel, K., Bergstrand, M., Eklund, J. (2016). Maintaining knife sharpness in industrial meat cutting: A matter of knife or meat cutter ability. *Applied Ergonomics, 56*, 92-100

Keir, P. J., Farias Zuniga, A., Mulla, D. M., & Somasundram, K. G. (2021). Relationships and Mechanisms Between Occupational Risk Factors and Distal Upper Extremity Disorders. *Human Factors, 63*(1), 5-31.

La Delfa, N. J., & Potvin, J. R. (2017). A musculoskeletal model to estimate the relative changes in wrist strength due to interacting wrist and forearm postures. *Computer Methods in Biomechanics and Biomedical Engineering, 20*(13), 1403-1411.
525

Latash, M. L. (2018). Muscle coactivation : Definitions, mechanisms, and functions. *Journal of Neurophysiology*, 120(1), 88-104.

526

527

Lemerle, B., & Chicot, B. (2018). *Observatoire des troubles musculo-squelettiques des actifs agricoles : Bilan national 2012-2016* (N° 12030). Caisse centrale MSA.

528

529

Li, C. Y., & Sung, F. C. (1999). A review of the healthy worker effect in occupational epidemiology. *Occupational medicine*, 49(4), 225-229.

530

531

Maithani, H., Corrales Ramon, J. A., Lequievre, L., Mezouar, Y., & Alric, M. (2021). Exoscarne : Assistive strategies for an industrial meat cutting system based on physical human-robot interaction. *Applied Sciences*, 11(9), 3907.

532

533

534

Marieb, E. N. (1993). *Anatomie et physiologie humaines* (2e éd). De Boeck université.

535

Marsot, J., Claudon, L., & Jacqmin, M. (2007). Assessment of knife sharpness by means of a cutting force measuring system. *Applied Ergonomics*, 38(1), 83-89.

536

537

Mayer, T. A., Harsch, A. K., Koska, D., Hensel-Unger, R., & Maiwald, C. (2022). Effects of an active hand exoskeleton on forearm muscle activity in industrial assembly grips. *Work*, 72(4), 1577-1591.

538

539

540

McAtamney, L., & Nigel Corlett, E. (1993). RULA : A survey method for the investigation of work-related upper limb disorders. *Applied Ergonomics*, 24(2), 91-99.

541

542

McGorry, R., L. Young, S., Murphy, P., & Brogmus, G. (2000). Experimental appraisal of a manual task evaluator. *International Journal of Industrial Ergonomics*, 25(3), 265-274.

543

544

McGorry, R. W. (2001). A system for the measurement of grip forces and applied moments during hand tool use. *Applied Ergonomics*, 32(3), 271-279.

545

546

McGorry, R. W., Dempsey, P. G., & O'Brien, N. V. (2004). The effect of workstation and task variables on forces applied during simulated meat cutting. *Ergonomics*, 47(15), 1640-1656.

547

548

Moore, J. S., & Garg, A. (1994). Upper extremity disorders in a pork processing plant : Relationships between job risk factors and morbidity. *American Industrial Hygiene Association Journal*, 55(8), 703-715.

549

550
551

Moore, J. S., & Garg, A. (1995). The Strain Index : A proposed method to analyze jobs for risk of distal upper extremity disorders. *American Industrial Hygiene Association Journal*, 56(5), 443-458.

552

553

Moritomo, H., Apergis, E. P., Herzberg, G., Werner, F. W., Wolfe, S. W., & Garcia-Elias, M. (2007). 2007 IFSSH Committee Report of Wrist Biomechanics Committee : Biomechanics of the So-Called Dart-Throwing Motion of the Wrist. *The Journal of Hand Surgery*, 32(9), 1447-1453.

554

555

556

Muller, A., Pontonnier, C., Puchaud, P., & Dumont, G. (2019). CusToM : A Matlab toolbox for musculoskeletal simulation. *The Journal of Open Source Software*, 4(33), 1-3.

557

558

Neumann, W. P., Motiwala, M., & Rose, L. M. (2020). A comparison of work-rest models using a "breakpoint" analysis raises questions. *IISE Transactions on Occupational Ergonomics and Human Factors*, 8(4), 187-194

559

560

561

NF ISO 11228-3. (2007, novembre). Afnor EDITIONS.

562

Nordander, C., Ohlsson, K., Akesson, I., Arvidsson, I., Balogh, I., Hansson, G.-A., Strömberg, U., Rittner, R., & Skerfving, S. (2009). Risk of musculoskeletal disorders among females and males in repetitive/constrained work. *Ergonomics*, 52(10), 1226-1239.

563

564

565

Nuzzo, J. L., Taylor, J. L., & Gandevia, S. C. (2019). CORP : Measurement of upper and lower limb muscle strength and voluntary activation. *Journal of Applied Physiology, 126*(3), 513-543.

566

567

Occhipinti, E., & Colombini, D. (2007). Updating reference values and predictive models of the OCRA method in the risk assessment of work-related musculoskeletal disorders of the upper limbs. *Ergonomics*, 50(11), 1727-1739.

568

569

570

Pontonnier, C., De Zee, M., Samani, A., Dumont, G., & Madeleine, P. (2014). Strengths and limitations of a musculoskeletal model for an analysis of simulated meat cutting tasks. *Applied ergonomics*, 45(3), 592-600.

571

572

573

Pontonnier, C., Dumont, G., de Zee, M., Samani, A., & Madeleine, P. (2012). Cutting Force and EMG Recordings for Ergonomics Assessment of Meat Cutting Tasks : Influence of the Workbench Height and the Cutting Direction on Muscle Activation Levels. *Volume 4: Advanced*

574

575
576

Manufacturing Processes; Biomedical Engineering; Multiscale Mechanics of Biological Tissues;

577

Sciences, Engineering and Education; Multiphysics; Emerging Technologies for Inspection.

578

Pontonnier, C., Marie, S., Chander, D., Kirchhofer, S., & Gréau, M. (2021). Evaluating the action

579

detection of an active exoskeleton : A muscle-control synchronicity approach for meat cutting

580

assistance. Computer Methods in Biomechanics and Biomedical Engineering.

581

Potvin, J. R. (2012). Predicting maximum acceptable efforts for repetitive tasks : An equation based on

582

duty cycle. Human Factors, 54(2), 175-188.

583

Puchaud, P., Sauret, C., Muller, A., Bideau, N., Dumont, G., Pillet, H., & Pontonnier, C. (2020). Accuracy

584

and kinematics consistency of marker-based scaling approaches on a lower limb model : A

585

comparative study with imagery data. Computer Methods in Biomechanics and Biomedical

586

Engineering, 23(3), 114-125.

587

Savescu,A., Cuny-Guerrier, A., Wild ,P., Reno, G. , Aublet-Cuvelier, A., Claudon, L. (2018) Objective

588

assessment of knife sharpness over a working day cutting meat, Applied Ergonomics, 68(4),

589

109-116.

590

Silvin, S. (1999). Sollicitations biomécaniques des opérateurs dans les ateliers de découpe de viande

591

[Thèse d'exercice]. Université de Nancy I.

592

Tappin, D. C., Bentley, T. A., & Vitalis, A. (2008). The role of contextual factors for musculoskeletal

593

disorders in the New Zealand meat processing industry. Ergonomics, 51(10), 1576-1593.

594

Tirloni, A. S., Dos Reis, D. C., Tirloni, S. F., & Moro, A. R. P. (2020). Exertion Perception When

595

Performing Cutting Tasks in Poultry Slaughterhouses : Risk Assessment of Developing

596

Musculoskeletal Disorders. International Journal of Environmental Research and Public

597

Health, 17(24), 9534.

598

Tirloni SF, Tirloni AS, Roqueiro N, Díaz Merino EA, Schmidt Alves Díaz Merino G, Moro A.R.P.

599

(2021). Cutting force measurement: Hand tool instrumentation used in slaughterhouses - a

600

systematic review. EXCLI J. 2021 Apr 13;20:727-747.
601

Tomezzoli, A., Schuster, A., Dumont, G., & Pontonnier, C. (2023). *Effect of mass addition on upper limb*

602

*joint torques during meat cutting tasks: A parametric study*. 48th Congres of the Société de

603

Biomecanique (2023), Grenoble.

604

Villalobos, A., Mac Cawley, A. (2022) Prediction of slaughterhouse workers' RULA scores and knife

605

edge using low-cost inertial measurement sensor units and machine learning algorithms,

606

Applied Ergonomics,98(1),103556

607

Wu, G., van der Helm, F. C. T., Veeger, H. E. J. D., Makhsous, M., Van Roy, P., Anglin, C., Nagels, J.,

608

Karduna, A. R., McQuade, K., Wang, X., Werner, F. W., Buchholz, B., & International Society of

609

Biomechanics. (2005). ISB recommendation on definitions of joint coordinate systems of

610

various joints for the reporting of human joint motion--Part II: Shoulder, elbow, wrist and

611

hand. *Journal of Biomechanics*, 38(5), 981-992.

612

Xia, T., & Law, L. (2015). Wrist joint torque-angle-velocity performance capacity envelope evaluation

613

and modelling. *International Journal of Human Factors Modelling and Simulation*, 5(1), 33-52.

614

615

616

617

618

619

620

621

622

623

624

625

626

627

628

629
SUPPLEMENTARY MATERIAL

630

631

The data presented in the following pages correspond the descriptive representation of the biomechanical quantities investigated during the task for each subject individually. For sake of concision, only subject 1 was presented in the article. The first table summarizes general information about the cutting task for each subject.

632

633

634

635

<caption>Table 1: Cutting task summary parameters: Cycle time, number of exertions, frequency of exertions, average and peak cutting force and moment. Mean (+/- SD)</caption>

636

637

<table><thead><tr><th rowspan="2">Subject</th><th rowspan="2">CT (s)</th><th rowspan="2">Number of exertions</th><th rowspan="2">Frequency of exertions (/min)</th><th colspan="2">Cutting Force (N)</th><th colspan="2">Cutting Moment (Nm)</th></tr><tr><th>Average</th><th>Peak</th><th>Average</th><th>Peak</th></tr></thead><tbody><tr><td>S1</td><td>53 (-)</td><td>28 (1)</td><td>31.4 (0.7)</td><td>24.2 (3.2)</td><td>79.9 (10.8)</td><td>1.2 (0.1)</td><td>5.0 (1.4)</td></tr><tr><td>S2</td><td>71 (-)</td><td>42 (3)</td><td>35.2 (2.9)</td><td>21.0 (2.1)</td><td>104.7 (11.0)</td><td>1.0 (0.0)</td><td>4.2 (0.6)</td></tr><tr><td>S3</td><td>21 (-)</td><td>14 (3)</td><td>38.4 (8.2)</td><td>23.7 (0.8)</td><td>58.1 (5.4)</td><td>1.4 (0.1)</td><td>5.1 (0.4)</td></tr><tr><td>S4</td><td>31 (-)</td><td>13 (3)</td><td>24.8 (5.0)</td><td>20.5 (3.8)</td><td>57.7 (7.0)</td><td>1.4 (0.2)</td><td>4.5 (0.5)</td></tr><tr><td>S5</td><td>52 (-)</td><td>28 (4)</td><td>31.6 (4.1)</td><td>29.9 (1.5)</td><td>90.8 (3.2)</td><td>1.8 (0.1)</td><td>5.1 (0.4)</td></tr><tr><td>S6</td><td>75 (-)</td><td>40 (8)</td><td>32.2 (6.6)</td><td>21.5 (2.5)</td><td>67.8 (9.3)</td><td>1.6 (0.1)</td><td>5.9 (0.4)</td></tr></tbody></table>

638
<figure><img src="image_17.png" /></figure>

<figure><img src="image_18.png" /></figure>

<figure><img src="image_19.png" /></figure>

<figure><img src="image_20.png" /></figure>

<figure><img src="image_21.png" /></figure>

<figure><img src="image_22.png" /></figure>

Figure 1. Wrist flexion-extension for Subject2: distribution of joint angles frequencies, and

distribution of cutting force, wrist flexion and extension torque and effort depending on wrist flexion

and extension angles
<figure><img src="image_23.png" /></figure>

<figure><img src="image_24.png" /></figure>

<figure><img src="image_25.png" /></figure>

<figure><img src="image_26.png" /></figure>

<figure><img src="image_27.png" /></figure>

<figure><img src="image_28.png" /></figure>

Figure 2. Wrist radio-ulnar deviation for Subject 2: distribution of joint angles frequencies, and

distribution of cutting force, wrist radial and ulnar torque and effort depending on wrist radial and

ulnar angles
<figure><img src="image_29.png" /></figure>

<figure><img src="image_30.png" /></figure>

<figure><img src="image_31.png" /></figure>

<figure><img src="image_32.png" /></figure>

<figure><img src="image_33.png" /></figure>

<figure><img src="image_34.png" /></figure>

647

<caption>Figure 3. Wrist flexion-extension for Subject3: distribution of joint angles frequencies, and</caption>

<caption>distribution of cutting force, wrist flexion and extension torque and effort depending on wrist flexion</caption>

<caption>and extension angles</caption>
<figure><img src="image_35.png" /></figure>

<figure><img src="image_36.png" /></figure>

<figure><img src="image_37.png" /></figure>

<figure><img src="image_38.png" /></figure>

<figure><img src="image_39.png" /></figure>

<figure><img src="image_40.png" /></figure>

651

652

653

654

<caption>Figure 3. Wrist radio-ulnar deviation for Subject 3: distribution of joint angles frequencies, and distribution of cutting force, wrist radial and ulnar torque and effort depending on wrist radial and ulnar angles</caption>
<figure><img src="image_41.png" /></figure>

<figure><img src="image_42.png" /></figure>

<figure><img src="image_43.png" /></figure>

<figure><img src="image_44.png" /></figure>

<figure><img src="image_45.png" /></figure>

<figure><img src="image_46.png" /></figure>

655

Figure 4. Wrist flexion-extension for Subject4: distribution of joint angles frequencies, and

distribution of cutting force, wrist flexion and extension torque and effort depending on wrist flexion

and extension angles
<figure><img src="image_47.png" /></figure>

<figure><img src="image_48.png" /></figure>

<figure><img src="image_49.png" /></figure>

<figure><img src="image_50.png" /></figure>

<figure><img src="image_51.png" /></figure>

<figure><img src="image_52.png" /></figure>

659

660

661

662

<caption>Figure 5. Wrist radio-ulnar deviation for Subject1: distribution of joint angles frequencies, and distribution of cutting force, wrist radial and ulnar torque and effort depending on wrist radial and ulnar angles</caption>
<figure><img src="image_53.png" /></figure>

<figure><img src="image_54.png" /></figure>

<figure><img src="image_55.png" /></figure>

<figure><img src="image_56.png" /></figure>

<figure><img src="image_57.png" /></figure>

<figure><img src="image_58.png" /></figure>

<caption>Figure 6. Wrist flexion-extension for Subject5: distribution of joint angles frequencies, and distribution of cutting force, wrist flexion and extension torque and effort depending on wrist flexion and extension angles</caption>
<figure><img src="image_59.png" /></figure>

<figure><img src="image_60.png" /></figure>

<figure><img src="image_61.png" /></figure>

<figure><img src="image_62.png" /></figure>

<figure><img src="image_63.png" /></figure>

<figure><img src="image_64.png" /></figure>

<caption>Figure 7. Wrist radio-ulnar deviation for Subject 5: distribution of joint angles frequencies, and distribution of cutting force, wrist radial and ulnar torque and effort depending on wrist radial and ulnar angles</caption>
<figure><img src="image_65.png" /></figure>

<figure><img src="image_66.png" /></figure>

<figure><img src="image_67.png" /></figure>

<figure><img src="image_68.png" /></figure>

<figure><img src="image_69.png" /></figure>

<figure><img src="image_70.png" /></figure>

Figure 8. Wrist flexion-extension for Subject6: distribution of joint angles frequencies, and

distribution of cutting force, wrist flexion and extension torque and effort depending on wrist flexion

and extension angles
<figure><img src="image_71.png" /></figure>

<figure><img src="image_72.png" /></figure>

<figure><img src="image_73.png" /></figure>

<figure><img src="image_74.png" /></figure>

<figure><img src="image_75.png" /></figure>

<figure><img src="image_76.png" /></figure>

<caption>Figure 9. Wrist radio-ulnar deviation for Subject 6: distribution of joint angles frequencies, and distribution of cutting force, wrist radial and ulnar torque and effort depending on wrist radial and ulnar angles</caption>