# Evaluation of lower back and lower limb kinetics while lifting a baby dummy in squatting, kneeling and standing postures

Diana Pardo Ramos, Antoine Muller, Raphael Dumas, Adriana Savescu

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Diana Pardo Ramos, Antoine Muller, Raphael Dumas, Adriana Savescu. Evaluation of lower back and lower limb kinetics while lifting a baby dummy in squatting, kneeling and standing postures. International Journal of Industrial Ergonomics, 2026, 113, 10.1016/j.ergon.2026.103920. hal-05535007

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# Evaluation of lower back and lower limb kinetics while lifting a baby dummy in squatting, kneeling and standing postures

Diana Pardo Ramos<sup>a,b</sup>, Antoine Muller<sup>a,b</sup>, Raphael Dumas<sup>a</sup>, Adriana Savescu<sup>c,*</sup>

## ARTICLE INFO

### Keywords:

Musculoskeletal disorders

Intersegmental moments

Markerless motion capture

## ABSTRACT

Musculoskeletal disorders affect childcare workers at the lower back and the lower limbs. Childcare professionals lift children while adopting standing, kneeling and squatting postures. The risks associated with lifting from standing postures have been extensively evaluated, but evidence remains insufficient regarding the adoption of kneeling or squatting postures. This study aimed to estimate peak intersegmental moments at the L5/S1, hips and knee joints during a lifting activity in these three postures. This biomechanical evaluation was conducted under controlled laboratory conditions using two baby dummies of 2.7 kg and 10 kg. Joint kinetics was assessed using tri-dimensional video data and ground reaction forces. Results suggest that both lifting posture and dummy's load impact peak intersegmental magnitudes in all the joints. Lifting from a standing posture using the 10 kg baby dummy presented the highest peak intersegmental moments at the L5/S1 and the hip joints, with associated magnitudes of 228 Nm and 131 Nm respectively. These magnitudes decreases around 20% in squatting and 40% in kneeling postures. In contrast, the solicitations at the knee joint were higher in squatting (75 Nm) and kneeling (92 Nm) postures. These orders of magnitude were comparable to those found in the literature using classical loads of equal or greater mass, likely due to the postural exigence related to the type of load (a baby dummy) and grip (under the armpits). However, considering the work specificities in a nursery, the current recommendations for manual material handling cannot be directly followed for childcare workers.

## 1. Introduction

Musculoskeletal Disorders (MSDs) are alterations of the musculo-skeletal system that mainly affect the muscles, tendons and nerves (Putz-Anderson et al., 1997). Childcare workers have a high incidence of musculoskeletal disorders MSDs (Bright and Calabro, 1999) and low back pain (Rossi et al., 2013). In particular, 92% of occupational diseases recognized in this professional sector in France are related to periarticular conditions (CNAM-DRP-MStat, 2021).

Childcare professionals are highly exposed to manual material handling (MMH) activities. Lifting a child is the most frequently manual handling activity in nurseries, with a frequency of around 8 lifts per hour (Holtermann et al., 2020; Labaj et al., 2019). Higher lifting frequencies are observed with younger children (<2.5 years), especially during transfers onto changing tables and into cribs (King et al., 1996; Labaj et al., 2019; Sanders and Morse, 2005). Nursery furniture can be adapted in order to decrease lifting exposure (e.g. stairs that child can climb to

reach the change station, cribs at the ground level) (SPF Emploi, Travail et Concertation sociale, 2015). However, these solutions require children to walk, which they cannot do until they are at least 12 months old.

Child lifting is commonly associated with standing postures involving a forward trunk inclination of 30° or above (Holtermann et al., 2020), but they are also frequent in kneeling and squatting postures (Holtermann et al., 2020; Labaj et al., 2016). These postures have been considered as a source of the higher incidence of MSDs in this professional field, in particular at the lower back (Bright and Calabro, 1999; McGrath, 2007). Epidemiological studies have demonstrated a strong causal relationship between lifting from a standing posture and MSDs at the lower back (Putz-Anderson et al., 1997) in work fields other than childcare. In contrast, there is insufficient evidence to establish a link between lifting a load from kneeling or squatting postures and MSDs.

Laboratory outcomes suggest that workers who adopt kneeling postures are more exposed than those who adopt standing or sitting postures, particularly for the lower back (Gallagher, 2005) and for the knee

<footnote><sup>a</sup> Univ Lyon, Univ Gustave Eiffel, Univ Claude Bernard Lyon 1, LBMC UMR T_9406, F-69622, Lyon, France</footnote>

<footnote><sup>b</sup> Conseil Départemental du Val de Marne, Direction des Crèches, 94000, Créteil, France</footnote>

<footnote><sup>c</sup> INRS, Conception - Equipements de Protection - Interfaces Homme-Machine, Nancy, France</footnote>

<footnote>* Corresponding author.</footnote>

<footnote>E-mail address: adriana.savescu@inrs.fr (A. Savescu).</footnote>
(Andersen et al., 2016; Ditchen et al., 2015). Specifically, lifting a load from a kneeling posture can place even greater strain on the lower back compared to lifting from a standing posture using a stoop technique (Gallagher et al., 1994). Nonetheless, these studies only considered occupational fields that involves vertical restrictions, as is the case of underground coalmines or aircraft baggage handlers. The specific risks associated with lifting a load—in this case a child—from squatting or kneeling positions remain underexplored.

Intersegmental moments are commonly used to characterize the biomechanical risk factors of MSD during MMH as they are a good predictor of pain and discomfort at the lower back (Gallagher, 2005; Marras et al., 1993). Only a few studies have evaluated joint kinetics during child lifting, either in situ (Labaj et al., 2016) or under controlled laboratory conditions with baby dummies (Kim et al., 2022). These studies, however, have focused exclusively on lifting from standing postures. Although lifting from kneeling and squatting postures have been identified in situ, the complexity of the work activity has precluded its biomechanical characterization. A first step under controlled laboratory conditions is therefore required to expand current knowledge on the biomechanical solicitations related to a lifting task, using a childlike load, from these postures, using technologies that provide accurate measurements but are difficult to implement in situ (such as force plates).

The aim of this study is then to characterize a lifting task from standing, squatting and kneeling postures under controlled laboratory conditions. The peak intersegmental moments at the lower back, hips, and knees while lifting two baby dummies of different mass were assessed and compared to those reported in current MMH literature.

## 2. Methods

### 2.1. Experimental protocol

Eight healthy participants (one male and seven females, BMI = 24.6 ± 3.8 kg/m², age = 28 ± 6 years) participated in the experimental protocol with the approval of the ethical committee of University Gustave Eiffel, France. Participants did not experience any MSDs in the six months preceding the experimental session, and had not undergone any surgery in the previous three months. Although participation was open

to individuals regardless their profession and experience, no childcare professionals took part in the study. Demographics of each participants is shown in Table S1 of supplementary materials.

The tasks consisted of lifting a baby dummy from ground level while adopting kneeling, squatting, and standing as initial postures. To standardize the postures, participants were required to replicate the postures shown in Fig. 1 as closely as possible.

Participants were asked to position themselves in front of the dummy at a self-selected distance in the initial position over two force platforms, keeping one foot/knee on each platform. From the initial posture, they had to reach the baby dummy with both hands symmetrically positioned under its armpits, bring it straight towards their chest, hold the posture for a few seconds, and then lower the baby dummy back to the initial position (Fig. 2). Two baby dummies of 2.7 kg weight, 50 cm height and 10 kg weight, 76 cm height were used. The use of a baby dummy was chosen over typical loads (e.g., boxes) to account for a realistic grip during child lifting, which is generally performed under the armpits. The dummies were limited to a mass of 10 kg, corresponding to the average weight of a one-year-old child whose lifting is unavoidable.

A total of six posture-load trials were evaluated (3 postures x 2 loads), with three consecutive lifts performed for each trial. To minimize bias due to participant fatigue, a minimum of 1 min of rest was provided between trials (average trial duration: 40 s). The order of the trials was randomized for each participant to prevent bias in lifting performance related to fatigue, task difficulty, or learning effects. Participants were informed of the next posture-load combination during the rest period between trials.

Participants were familiarized with the task, the postures, and the baby dummies before recordings began. During the recordings, they were required to keep the feet (for standing and squatting postures) or the feet and knees (for the kneeling posture) static and in contact with the force platforms throughout the repetitions. No other body segments were allowed to contact the force platforms at any point. Lifting strategy was not imposed, allowing participants to choose the approach that worked best for them (e.g., flexing the knees, the trunk, or both).

### 2.2. Data acquisition

Ten Qualisys Miqus Video cameras (sampling frequency at 50 Hz)

<figure><img src="image_2.png" /><figcaption>**Fig. 1.** Example of the initial standing, squatting and kneeling postures.</figcaption></figure>
<figure><img src="image_3.png" /><figcaption>**Fig. 2.** Example of a lifting sequence in standing, squatting, and kneeling postures with a 10 kg baby dummy.</figcaption></figure>

were used in this experimental protocol. The cameras were synchro-
nized and calibrated using Qualysis Track Manager. Camera calibration
was performed using an L-shape object to define the laboratory coor-
dinate system, and a calibration wand to estimate extrinsic camera pa-
rameters. Ground reaction forces were measured using two
synchronized force platforms (Treadmetrix, sampling frequency at 2000
Hz).

2.3. *Lifting phase definition*

Lifting was defined as the period from when participants began reaching for the baby dummy from the initial position (Fig. 2: start of the lifting phase) until they returned to the initial posture while holding the dummy (Fig. 2: end of the lifting phase). These events were identified manually from video recordings for each of the three repetitions performed by the participants. Repetitions were excluded if participants did not start from a static posture.

2.4. Kinematics and kinetics estimation

Whole body kinematics were computed using Theia3D (Theia Mar-
kerless v2023.1) from video recordings. Intersegmental moments of L5/
S1, hips and knee joints were estimated using three-dimensional kine-
matics data, and ground reaction forces and moments, using a biome-
chanical model as described by Lahkar et al. (2022) implemented in
Visual3D (C-motion, v2022.10.2). Body segment inertial parameters
(BSIPs) for each participant were calculated according to Dumas and

Wojtusch (2018). Intersegmental moments and ground reaction forces were post-processed using a fourth-order Butterworth low-pass filter (cut frequency at 12 Hz).

The amplitude of the L5/S1, hip, and knee intersegmental moments was computed for all repetitions. Due to the symmetry of the task, the average amplitude of the intersegmental moments at the right and left hip and knee joints was considered. The peak intersegmental moment amplitude for each repetition in each trial was then obtained and averaged. In this document, this mean value is referred to the peak intersegmental moment.

3. Results

Peak intersegmental moments at the L5/S1, the hips and the knee
joints for each posture-load combination are shown in **Fig. 3**. Mean and
standard deviation magnitudes are presented in **Table 1**, together with
peak intersegmental moments reported in MMH literature.

The highest peak intersegmental moment was observed at the L5/S1
joint when participants lifted a 10 kg baby dummy from a standing
posture (median: 228 Nm). Across all configurations, peak interseg-
mental moments at the L5/S1 joint were consistently highest in the
standing posture. They decreased in squatting posture (26.6% and
23.3%) and in the kneeling posture (39.2% and 39.1%) with the 2.7 kg
and the 10 kg baby dummies, respectively. Similarly, peak interseg-
mental moments at the hip joint decreased in the squatting posture
(33.2% and 26.7%) and in the kneeling posture (47.4% and 41.7%)
compared to the standing posture. In contrast, peak intersegmental
<figure><img src="image_4.png" /><figcaption>**Fig. 3.** Peak intersegmental moments for L5/S1 (□, red), hip (X, blue) and knee (O, green) joints by trial. Each point corresponds to a participant. Box and Whisker plot represent the minimum, 25th quartile, median, 75th quartile, maximum and outliers. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)</figcaption></figure>

moments at the knee joint increased in squatting (223% and 204%), and kneeling postures (250% and 270%).

Intersegmental moments were higher when lifting the 10 kg dummy compared to the 2.7 kg dummy for all joints. Increasing the load by approximately 7 kg resulted in a 15 to 20% increase in moments at both the L5/S1 and hip joints. The load showed to have less influence on the knee joint, particularly when participants adopted the squatting or standing postures.

Concerning the instant at which peak intersegmental moments occur during the lifting cycle, intersegmental moments at all joints were lowest at the beginning and reached their peak during the baby dummy lifting phase, except at the knee in the kneeling and squatting postures (Fig. S1–S8 in supplementary material).

## 4. Discussion

This study aimed to estimate peak intersegmental moments at the L5/S1, the hips and the knee joints during a lifting task from three postures commonly used during childcare under controlled laboratory conditions.

The order of magnitudes reported in the present study using baby dummies are comparable to those in the literature using regular loads, as shown in Table 1. Peak intersegmental moments at L5/S1 joint are greater to 100 Nm regardless of the initial posture or the load mass, and they reach maximum peaks of 228 Nm while lifting the 10 kg baby dummy from a standing posture. These orders of magnitudes are comparable to those reported in the literature with loads weighting up to 23 kg, although this study limited the mass of the baby dummy to 10 kg. Lifting a 20 kg load in laboratory conditions has been associated to peak intersegmental moments of around 210 Nm (Tröster et al., 2022). This

level of solicitation has been considered as a biomechanical risk factor for the lower back. The present study presented similar magnitudes while lifting a baby dummy 10 kg lighter, suggesting that the type of load plays a major role in joint solicitation. It is likely that grip a baby dummy under the armpits induces the participants to place far from the dummy and to flex their back and their knees to place correctly their hands. Likewise, the level of joint solicitation at the hips and the knees is comparable to the literature, with peak intersegmental moments of around 100 Nm and 30 Nm, respectively.

Peak intersegmental moments while lifting from squatting and kneeling postures cannot be directly compared to the literature for any of the joints. Two studies have evaluated L5/S1 moments during lifting in kneeling posture (Gallagher et al., 1994; Splittstoesser et al., 2007). Unfortunately, substantial differences in the experimental protocols and the calculation method of joint kinetics compared to those used in the present study make such comparisons unfeasible.

Standing posture shows greater magnitudes at L5/S1 and hip joints than squatting or kneeling postures although kneeling posture imposes a higher biomechanical solicitation to the knees. This is likely due to the variation of the lever arm between the ground reaction forces and the joints across the postures. In particular, intersegmental moments at the knee joint reach their minimum magnitude during the dummy lifting phase in kneeling posture (Fig. S1–S8 in supplementary material). That finding should not be interpreted to mean that kneeling is better than standing or squatting postures for lifting a load. While kneeling, forces are mainly applied directly at the knee joint that has been considered as a risk factor for patellofemoral pathologies (Porter et al., 2010). Rather, it indicates that joint solicitations depend on the adopted posture and vary throughout the lifting cycle.

Lifting heavier loads logically involves higher biomechanical
<caption>**Table 1**</caption>

Mean and standard deviation of peak intersegmental moments [N.m] at L5/S1, hip and knee joints obtained in this study and in the literature.

<table><thead><tr><th rowspan="2">Study</th><th rowspan="2">Participants</th><th rowspan="2">Lifting posture</th><th rowspan="2">Technique</th><th rowspan="2">Load (kg)</th><th colspan="3">Joint</th></tr><tr><th>LJC</th><th>Hip</th><th>Knee</th></tr></thead><tbody><tr><td rowspan="2">Plamondon, (2010)</td><td>MMH experience</td><td rowspan="2">Standing</td><td rowspan="2">Not imposed</td><td>15-23</td><td>226 ± 37</td><td>-</td><td>-</td></tr><tr><td>Healthy volunteers</td><td>15-23</td><td>228 ± 43</td><td>-</td><td>-</td></tr><tr><td rowspan="6">Tröster et al. (2022)<sup>b</sup></td><td rowspan="6">MMH experience</td><td rowspan="3">Standing</td><td rowspan="3">Stoop</td><td>4</td><td>170 ± 7</td><td>-</td><td>-</td></tr><tr><td>8</td><td>180 ± 10</td><td>-</td><td>-</td></tr><tr><td>20</td><td>210 ± 5</td><td>-</td><td>-</td></tr><tr><td rowspan="3">Standing</td><td rowspan="3">Squat</td><td>4</td><td>180 ± 5</td><td>-</td><td>-</td></tr><tr><td>8</td><td>210 ± 10</td><td>-</td><td>-</td></tr><tr><td>20</td><td>230 ± 5</td><td>-</td><td>-</td></tr><tr><td rowspan="6">Hwang et al. (2009)<sup>a b</sup></td><td rowspan="6">Healthy volunteers</td><td rowspan="3">Standing</td><td rowspan="3">Stoop</td><td>5</td><td>153 ± 13</td><td>93 ± 13</td><td>80 ± 7</td></tr><tr><td>10</td><td>180 ± 7</td><td>106 ± 7</td><td>86 ± 7</td></tr><tr><td>15</td><td>213 ± 13</td><td>126 ± 7</td><td>100 ± 7</td></tr><tr><td rowspan="3">Standing</td><td rowspan="3">Squat</td><td>5</td><td>147 ± 7</td><td>73 ± 7</td><td>40 ± 7</td></tr><tr><td>10</td><td>186 ± 7</td><td>86 ± 13</td><td>27 ± 7</td></tr><tr><td>15</td><td>226 ± 20</td><td>113 ± 13</td><td>13 ± 7</td></tr><tr><td rowspan="4">Van Der Have et al. (2019)<sup>b</sup></td><td rowspan="4">Healthy volunteers</td><td rowspan="2">Standing</td><td>Stoop</td><td>10</td><td>180 ± 50</td><td>105 ± 35</td><td>50 ± 20</td></tr><tr><td>Squat</td><td>10</td><td>175 ± 75</td><td>80 ± 30</td><td>60 ± 10</td></tr><tr><td rowspan="2">Standing</td><td rowspan="2">Not imposed</td><td>4.6</td><td>121 ± 10</td><td>102 ± 10</td><td>89 ± 37</td></tr><tr><td>7.6</td><td>134 ± 9</td><td>126 ± 25</td><td>105 ± 35</td></tr><tr><td rowspan="3">Kim et al. (2022)<sup>a</sup></td><td rowspan="3">Healthy volunteers</td><td rowspan="3">Standing</td><td rowspan="3">Not imposed</td><td>9.8</td><td>147 ± 19</td><td>147 ± 22</td><td>95 ± 30</td></tr><tr><td>11 - 13</td><td>156 ± 26</td><td>-</td><td>-</td></tr><tr><td>13 - 17</td><td>176 ± 41</td><td>-</td><td>-</td></tr><tr><td rowspan="4">Labaj et al. (2019)</td><td rowspan="4">Childcare workers</td><td rowspan="4">Standing</td><td rowspan="4">Not imposed</td><td>2.5 - 11</td><td>156 ± 26</td><td>-</td><td>-</td></tr><tr><td>11 - 13</td><td>176 ± 41</td><td>-</td><td>-</td></tr><tr><td>13 - 17</td><td>151 ± 50</td><td>-</td><td>-</td></tr><tr><td>2.7</td><td>170 ± 21</td><td>94 ± 14</td><td>39 ± 18</td></tr><tr><td rowspan="3">This study</td><td rowspan="3">Healthy volunteers</td><td rowspan="3">Standing</td><td rowspan="3">Not imposed</td><td>10</td><td>204 ± 18</td><td>110 ± 11</td><td>37 ± 18</td></tr><tr><td>2.7</td><td>120 ± 19</td><td>61 ± 9</td><td>77 ± 15</td></tr><tr><td>10</td><td>159 ± 27</td><td>80 ± 14</td><td>76 ± 22</td></tr><tr><td rowspan="2">This study</td><td rowspan="2">Healthy volunteers</td><td rowspan="2">Squatting</td><td rowspan="2">Not imposed</td><td>2.7</td><td>103 ± 11</td><td>54 ± 6</td><td>86 ± 12</td></tr><tr><td>10</td><td>123 ± 23</td><td>62 ± 10</td><td>98 ± 21</td></tr></tbody></table>

constraints for all the joints. This trend is also presented in the literature, which reported significant differences when mass increases from 4 to 8 kg to 20 kg. The present study consider loads of 2.7 and 10 kg but children in nurseries can weight 17 kg at 3 years old. Therefore, joint solicitations are expected to increase substantially with older children.

## 4.1. Points of vigilance during child manual handling

Some of the biomechanical risk factors associated with MMH activities are related to the frequency and duration of the task, the type of load, its mass, and its initial and final positions (Ferguson et al., 2005; Gallagher, 2005; Lavender et al., 2003), as well as the postures adopted during the activity (Gallagher, 2005; Von Arx et al., 2021). This study did not evaluate task frequency or duration, as these parameters are difficult to reproduce under laboratory conditions with baby dummies and non-professional participants. In contrast, this study provides information concerning the biomechanical solicitation at the lower back, the hips and the knees while lifting a baby dummy (type of load and mass) placed at the ground (initial and final position) in standing, squatting and kneeling postures (lifted postures).

Current MMH recommendations usually focus on modifying the distance from the load (as short as possible), the lifting posture (avoiding forward trunk bending), the placement of the load grip (at the top of the load) and the foot positioning (even or ipsilateral), among many others. Most of these parameters are not modifiable during child manual handling. The “load” (a child) is typically lifted from the armpits that forces to maintain a certain distance from the load, as it was observed in the present study using baby dummies. The dummy position and participant's foot position were fixed in this experimental protocol but it could be modifiable in real-work situations in order to reduce joint solicitations.

In a working environment, joint solicitation during MMH also depends on the worker experience (Plamondon, 2010). None of the participants in this study had professional experience lifting children,

however, peak intersegmental moments at the L5/S1 joint were comparable to those observed in childcare workers in real situations (mean: 156 ± 26 Nm) (Labaj et al., 2016). Unlike other work fields, children are a dynamic load with whom professionals must interact. Work experience is likely to help in managing the unpredictable nature of their movements (e.g., a child resisting being lifted). Such variables cannot be reproduced or evaluated under laboratory conditions, but the present study provides reference values and calculation methods that can be applied in further evaluations in situ.

No specific recommendations were found in the literature regarding lifting from squatting or kneeling postures, but the variables mentioned above could be applied to these cases. The aim of this work was not to develop recommendations on how to perform a lifting task in these postures, but rather to provide new insights into biomechanical constraints at the lower back and lower limbs. Our results showed that posture influences the magnitude of peak intersegmental moments, and should therefore be considered when developing recommendations to prevent MSDs during MMH activities. A key focus could be on mechanisms and strategies that help maintain balance during these tasks.

## 4.2. Limitations

This study presented a biomechanical evaluation of the lower back and the lower limbs constraints during lifting a baby dummy from postures typically observed in nurseries. A limitation of the results relates to its ecological validity. This study was limited to baby dummies weighing up to 10 kg (representing a one-year-old child) while children in nurseries may weigh up to 17 kg. However, child over one year (and over 10 kg) gradually gain independence, and lifting can sometimes be avoided. By contrast, lifting children under one year is unavoidable, which is why this study prioritized dummies representing that age group. The use of baby dummies instead of children removes the dynamic nature of a child, which may influence the magnitudes of intersegmental moments. However, baby dummies have already been used in the literature to

<footnote><sup>a</sup> Values multiplied to mean participant's body mass.</footnote>

<footnote><sup>b</sup> Values obtained from plots.</footnote>
characterize biomechanical risks factors of MSDs associated with childcare, as they reproduce child grip, mass, and morphology. For the purpose of this study, the use of baby dummies allows to standardize the task while avoiding ethical concerns related to the inclusion of a vulnerable population such as children under 3 years of age. In the same vein, the participants in this study were not childcare professionals. The contribution of professional experience, and thus the lifting strategies used to lift children, are not taken into account. However, this experimental protocol includes a controlled lifting activity that may conceal the gestures developed over years of professional practice. Finally, eight participants were included in this experimental protocol. Although a larger cohort would be ideal, the peak intersegmental moments were consistent across participants and comparable to those reported in the literature. Thus, the order of magnitudes presented in this study appear reliable and yield consistent results.

### 4.3. Future work

This study was motivated by health concerns in the childcare field. It biomechanically evaluates one task related to MSDs in this occupational context: lifting a child. Although different postures and load masses were tested, other parameters directly related to children or childcare workers were not included, mainly due to the difficulty of replicating them in the laboratory. It is therefore suggested that future work focus on an in situ evaluation. However, such an approach involves additional constraints, such as the choice of measurement system and the reliability of the acquired data, which are issues largely avoided in laboratory-based studies.

This study uses tri-dimensional video data for the estimation of joint kinematics. Although the accuracy of video data for the estimation of kinematic variables is still under evaluation for various tasks (Chaumeil et al., 2024; Kanko et al., 2021), it opens the possibility to apply this technology in situ. Likewise, this study made use of two force platforms to obtain reliable information on ground reaction forces, but these instruments are unsuitable in nursery settings. Therefore, future research should focus on alternative methods of estimating external forces in order to evaluate joint intersegmental moments.

## 5. Conclusions

Intersegmental moments at the L5/S1, the hip and the knee joints while lifting a baby dummy were found comparable to the orders of magnitude reported in the literature using conventional loads in standing posture. Peak magnitudes were comparable for load masses exceeding 10 kg those used in the present study, likely due to the load (a baby dummy) and the grip (under the armpits) imposed.

Peak intersegmental moments around 200 Nm while lifting a 10 kg baby dummy in standing posture, which has been identified in the literature as a potential biomechanical risk factor during MMH. Both, the lifting postures and the dummy mass had an influence in the magnitude of peak intersegmental moments. The L5/S1 and hip joints presented greater peak intersegmental moments in the standing posture, whereas the knee joint showed the lowest magnitudes in this posture. As expected, higher magnitudes were associated while lifting the 10 kg than the 2.7 kg baby dummy. However, changes were less evident at the knee joint and in the kneeling posture for all the joints.

Finally, most of current recommendations during a lifting task could not be directly transferred to child lifting. One possible strategy to reduce joint solicitations in the lower back and the lower limbs during childcare could be to focus on adapting lifting postures during child lifting.

This study represents a first step in evaluating biomechanical risk factors of MSDs during child lifting. It opens perspectives for an in situ evaluation in nurseries to account for individual characteristics, lifting strategies, and real child-worker interactions.

## CRediT authorship contribution statement

**Diana Pardo Ramos:** Writing – review & editing, Writing – original draft, Methodology, Investigation, Formal analysis, Data curation, Conceptualization. **Antoine Muller:** Writing – review & editing, Validation, Software, Methodology, Conceptualization. **Raphael Dumas:** Writing – review & editing, Validation, Supervision, Methodology, Conceptualization. **Adriana Savescu:** Writing – review & editing, Validation, Supervision, Methodology, Conceptualization.

## Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

## Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi.org/10.1016/j.ergon.2026.103920.

## Data availability

Data will be made available on request.

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