Exoskeleton for upper limbs in meat processing industry: Influence on muscle activity and physical effort

Introduction

Brazil ranked fourth in global pork production during the 2024 season, with an output of 4.5 million tons. Brazilian pork exports reached 1.352 million tons in the same year, according to the Brazilian Association of Animal Protein. ¹ “Brazil is home to some of the world's leading meat producers and exporters”. ²

Southern Brazil is responsible for 67% of total production and hosts most meat slaughtering and processing industries. These companies present “situations with the potential to compromise worker health and safety”. ³

The prevalence of musculoskeletal disorders among slaughterhouse workers has been widely documented in international studies, revealing a consistent pattern of physical impairment associated with the working conditions in this sector.

A total of 40.97% of evaluated workers were found to have soft tissue musculoskeletal disorders, with most performing repetitive movements (89.6%) and working shifts longer than six hours (78.9%). ⁴ These findings strengthen the link between physical overload and the development of occupational injuries.

The overall prevalence of musculoskeletal disorders among slaughterhouse workers was 64,9%, with symptoms most commonly affecting the hands and wrists (54.8%), elbows (45.2%), and lower back (43.5%). ⁵ Similarly, in another recent study of poultry slaughterhouse workers, 61.5% reported shoulder pain, 60.3% reported pain in the hands or wrists, and 35.9% reported pain in the lower back. ⁶ These findings demonstrate that musculoskeletal disorders represent a global and persistent issue, regardless of geographic location or slaughterhouse type.

The use of innovative technologies plays a fundamental role in improving working conditions and preventing occupational injuries, especially in jobs with high physical demands and repetitive movements, which are common in the meat processing and slaughter industries.

In industrial environments such as meat slaughtering and processing, ergonomic issues have been a constant challenge to worker health, representing significant biomechanical risks that require effective technological solutions. In this context, the use of passive exoskeletons has emerged as a promising approach to mitigating these risks.

The introduction of new technologies and applications is crucial in ergonomics, as they promote worker safety and well-being, prevent injuries, and improve performance.^7,8

The use of upper limb exoskeletons reduces muscle effort, particularly in the lateral and medial deltoids, thereby lowering biomechanical risk. ⁹

In addition, electromyography has proven effective in quantitatively identifying muscle contractions. ¹⁰ These approaches aim to improve working conditions and promote the health and comfort of workers.

Several studies involving various exoskeleton models applied to laboratory simulations have been conducted.^11–26

These studies indicate that wearable technologies positively impact the risk of injuries to the shoulders, elbows, spine, and hands and provide strong evidence that surface electromyography (sEMG) is a safe and effective method for muscle evaluation.

Some reports emphasize the need for field studies, in which other variables may interfere with the results. This observation underscores the importance of field tests with exoskeletons in real work situations, such as the practical studies conducted by some authors.^27,28 These investigations tested exoskeletons in production environments—the first in the vehicle assembly sector of the Ford Motor Company in Glendale, MI, USA, and the second in two John Deere factories.

Despite the growing interest in using exoskeletons to improve ergonomics and prevent injuries in the workplace, researchers have paid little attention to their applicability in environments such as slaughtering and meat processing industries. This study aimed to analyze the effectiveness of the exoskeleton in reducing physical effort in the upper limbs during repetitive dynamic activities in meat processing production lines, considering its usability.

Materials and methods

A field study was conducted at a representative meat processing company using a purposive sampling technique. The sampling was not based on the number of individuals evaluated but on the significance of their relationship to the investigated problem. This study employed a within-subjects design in which the same participants performed the tasks both with and without the use of the exoskeleton. Therefore, group randomization was not required, as each individual served as their own control.

Evaluated tasks

Seventeen activities were selected in which the shoulders performed dynamic flexion and abduction movements at angles between 45° and 90°.

The 4 first tasks (1-stocking sausage trolley, 2-stocking calabrese sausage, 3- hanging bacon, and 4-hanging fresh pork sausage) have similar characteristics involving the actions of hanging and unhanging processed products on trolleys. Each task requires a worker to walk very short distances to pick up products from a table or machine output and place them in trolleys.Tasks 5 and 6 (5-hanging reels on the overhead rail system and 6-unhanging reels from the overhead rail system) were performed by two workers who adopted an upright posture and repetitive upper limb movements. One worker performs the task of hanging reels, grabbing them with both hands, and lifting them to a position on the rails; the other worker unhangs the reels from the overhead system, grabbing them with both hands, and placing them on a side table.

Tasks 7 to 17 were 7: swine tenderloin removal, 8: belly primal separation, 9: shoulder primal deboning, 10: ham primal deboning, 11: deboning humerus, 12: detaching muscle, 13: swine carcass shoulder removal, 14: neck bone removal, 15: manual belly scraping, 16: total deboning, and 17: final trimming. They are performed in an overhead rail system in which pigs are brought to workstations where the workers are positioned standing facing the production line.

The line is continuous, and the pigs hung on the overhead rail system pass in front of the workers who must perform their tasks by cutting parts of the pig's carcass. Using knives in one hand and holding the pig with the other, workers performed specific tasks of cutting, scraping, and detaching meat from the pig carcass. On the other hand, the device that does not hold a knife is used to hold a piece of meat during cutting or hair scraping. In this overhead rail system process, 11 workers perform similar tasks with the same goal of cutting pork but removing different parts of the pig.

Figure 1 presents a macro flowchart of the industrial process, with the tasks selected for the study highlighted in black.

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Figure 1.

Industrial process flowchart.

Practical application of the exoskeleton and electromyograph

The exoskeleton model used in this study was EXYONE, manufactured in Brazil by Exygroup – Industrial Exoskeletons, designed to reduce the physical effort of the upper limbs. Figure 2 represents the use of the EXYONE exoskeleton by one of the 17 participants in the studied tasks in the meat slaughtering and processing industry production system.

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Figure 2.

Using the exoskeleton.

The electromyograph used was the Miotool – 400^® model, featuring four channels, a 14-bit analog-to- digital converter board, surface sensors for acquisition at 2000 samples per second, common mode rejection of 100 dB, and signals amplified with a gain of 1000 times. A disposable foam (3 M model 2223BRQ) was used as the electrode.

For this study, signal filtering was performed using a low-pass filter with a cutoff frequency of 500 Hz to remove high-frequency noise, and a high-pass filter with a cutoff frequency of 20 Hz to eliminate low-frequency components such as motion artifacts.

Results

Regarding the results presented by sEMG, the variables generated by Miotec Suit 1.0 software were: Peak (μV) and, Adjusted Mean (μV). The Adjusted Normalized Mean (%MVC) was selected to compare the values obtained during exoskeleton use and non-use as shown in Figure 3.

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Figure 3.

Normalized adjusted mean of the 4 studied muscles: columns indicate mean values; error bars represent 95% confidence intervals derived from Table 1.

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Table 1.

Average values with Confidence Intervals (CI) and statistical significance.

Muscle	Average with exo (CI)	Average without exo (CI)	p-value	Adjusted α (Bonferroni)	Statistical significance	Cohen's (d)	Effect size
Left anterior deltoid	13,3% MVC [9,8% – 16,8%]	15,3% MVC [11,9% – 18,8%]	0,0387	0,1548	No	−0,2843	Small
Left medial deltoid	17,0% MVC [10,0% – 24,1%]	22,4% MVC [14,8% – 30,0%]	0,0505	0,2020	No	−0,3486	Small
Right anterior deltoid	20,9% MVC [14,1% – 27,7%]	25,5% MVC [17,0% – 34,0%]	0,0232	0,0928	No	−0,2857	Small
Right medial deltoid	22,5% MVC [17,0% – 28,0%]	26,0% MVC [19,8% – 32,1%]	0,0110	0,0440	Yes	−0,2796	Small

The graphic indicates a reduction in the intensity and frequency of the signal captured by the sEMG when the exoskeleton was used. Therefore, there were gains in this aspect compared to non-use.

Table 1 presents the mean values of muscle activation with and without exoskeleton use, including the confidence intervals, p-values, and corresponding effect sizes. Overall, a trend toward reduced muscle activity was observed with the use of the device, although only the right medial deltoid showed a significant difference.

Figure 4 depicts the statistical analysis of the four muscles studied for each participant, where the average of the normalized peaks (peak) of the 17 participants was applied considering the use and non-use of the exoskeleton.

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Figure 4.

Average of normalized peak values (peak): columns indicate mean values; error bars represent 95% confidence intervals derived from Table 2.

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Table 2.

Peak values with Confidence Intervals (CI) and statistical significance.

Muscle	Average with exo (CI)	Average without exo (CI)	p-value	Adjusted α (Bonferroni)	Statistical significance	Cohen's (d)	Effect size
Left anterior deltoid	75,9% [64,8% – 87,0%]	91,9% [82,2% – 1015%]	0,0798	0,3192	No	−0,7255	Medium
Left medial deltoid	74,2% [61,2% – 87,3%]	97,0% [93,1% – 1009%]	0,0138	0,0552	No	−1,1196	Large
Right anterior deltoid	83,7% [73,9% – 93,5%]	93,5% [84,3% – 1027%]	0,0927	0,3708	No	−0,4894	Small
Right medial deltoid	84,9% [78,3% – 91,4%]	97,1% [93,3% – 1008%]	0,0138	0,0552	No	−1,0791	Large

Considering the normalized sEMG peak values of the four muscles evaluated across the 17 tasks, none showed a statistically significant difference.

However, overall, the mean normalized peak values were reduced with exoskeleton use compared with non-use, as shown in Table 2.

Of the 17 individuals who participated in the study, Figure 5 shows that during exoskeleton use, 23.5% reported applying very light effort (score 1) on the Borg Scale, while 76.5% indicated light effort (scores 2 and 3). In contrast, in the absence of the exoskeleton, 41.2% of the participants reported light effort (scores 2 and 3), and 58.8% reported moderate effort (scores between 4 and 6)

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Figure 5.

Borg Scale: Comparison of force application in the upper limb with and without exoskeleton use.

According to Questionnaire 02, the responses shown in Figure 6 demonstrate the results related to the usability of the passive upper-limb exoskeleton.

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Figure 6.

System Usability Scale (SUS).

Conceptually, the SUS establishes the acceptability parameters for a system. In this study, the concept of the system was adapted for the usability of wearable technology in the upper limbs of an exoskeleton.

The average score established by the SUS is 68. Of the 17 participants, 15 demonstrated excellent usability, one showed good acceptance of the usability of this exoskeleton, and one participant showed neutral acceptability.

Discussion

The results indicate a general trend of reduced muscle activity with the use of the exoskeleton, as demonstrated by the average activation levels presented in Table 1. Statistical analysis, conducted using Student's t-test and the Wilcoxon test with Bonferroni correction, revealed statistical significance only for the right medial deltoid muscle. In contrast, Table 2, which presents the peak muscle activation values, shows no statistically significant differences between the evaluated conditions.

Additionally, the calculation of effect size using paired Cohen's d coefficients allowed for a deeper analysis of the magnitude of the observed differences. For the muscles evaluated using MVC, the d values indicated small effects, suggesting that although there was a trend toward reduced muscle activation with the use of the device, this difference was modest and statistically uncertain. In contrast, the peak data revealed moderate to large effects in three muscles, with negative estimates, reinforcing the practical relevance of these findings even in the absence of statistical significance.

The negative direction of the estimators (d < 0) in all analyzed muscles suggests that, on average, the use of the exoskeleton is associated with lower muscle activation, which may reflect a reduction in biomechanical demand during task execution. These findings support the hypothesis that the device contributes to reducing muscular load, especially in the shoulder muscles, although the intensity of the effect varies depending on the muscle group and the type of measurement used (MVC vs. peak).

Considering these results, it is pertinent to discuss the applicability of exoskeletons in occupational settings. Their use has emerged as a promising strategy for improving ergonomics and mitigating the risk of injuries in activities involving repetitive physical effort and biomechanically unfavorable postures, such as those in meat production lines. The observed reduction in muscle activity, particularly in the deltoid muscles, suggests that the device may help reduce fatigue, discomfort, and physical strain.

For effective implementation, aspects such as anthropometric adjustments, physical space suitability, and adaptation to workers’ physiological characteristics must be considered. The possibility of incorporating the exoskeleton as personal protective equipment (PPE) reinforces its potential for integration into work routines. Moreover, evaluating its impact on productivity, worker acceptance, and organizational culture is essential for its adoption on an industrial scale.

Discussions on applicability should also consider other sectors with similar demands, such as vehicle assembly, logistics, and cargo handling, to extend the benefits of this technology beyond the meat processing sector. The incorporation of exoskeletons aligned with ergonomic strategies can foster safer, more efficient, and more sustainable work environments, thereby promoting occupational health and business competitiveness. The evolution of this technology, combined with longitudinal studies and adaptation to the specificities of different contexts, reveals its transformative potential for industrial environments.

Conclusions

This study aimed to analyze the usability of a specific passive exoskeleton model developed for the upper limbs, focusing on reducing physical effort during repetitive dynamic activities in meat processing production lines. The choice of field research was motivated by the need to expand studies related to exoskeleton applications in slaughterhouses.

For data collection, field research was conducted integrating the use of exoskeletons by workers in production lines, surface EMG, and two questionnaires to address the research problem. The collected data enabled the identification and analysis of results, ultimately providing answers to the research question.

The results of the sEMG analysis indicated a reduction in muscle activity in the left anterior deltoid, left medial deltoid, and right medial deltoid muscles during task execution with the exoskeleton. This suggests that its use may contribute to lowering muscular load in repetitive and biomechanically demanding tasks, such as those performed in industrial environments. This reduction may have a direct impact on the prevention of musculoskeletal injuries, reduction of fatigue, and improvement of workers’ occupational health.

Results consistent with those of the present study were observed in the evaluation of similar muscle groups, as reported in previous research. ²⁵ The hypothesis that the exoskeleton can be applied to other similar activities, regardless of whether they involve the processing of pork, beef, or poultry, was confirmed. This is particularly relevant when considering tasks involving continuous and repetitive lifting of the arm at angles greater than 45° for at least half of the task cycle time.

The technological model used in this study presented some fitting limitations reported by participants, indicating the need for improvements to accommodate different anthropometric profiles.

One of the main limitations of this technology, specifically the exoskeleton model for production lines, is related to spatial requirements. This exoskeleton expands the individual workspace area; therefore, additional physical space is required to prevent collisions and allow free mobility.

The effective contribution of this wearable technology is directly related to the reduction in biomechanical risk resulting from upper-limb physical effort, especially in the anterior and medial deltoid muscles of both arms. This was confirmed by the results of the subjective perception of the Borg Scale as well as by the sEMG findings, which indicated differences between the use and non-use of the exoskeleton. Given this background, the use of exoskeletons in meat-processing production lines has the potential to promote better performance with reduced physical effort, enabling application in a wide variety of similar work situations. Except for prolonged static activities involving arm lifting—which were not the focus of this study—the findings suggests that the studied exoskeleton could benefit both workers and companies.

The usability of the exoskeleton in a slaughterhouse setting presents a realistic opportunity to minimize the physical effort resulting from excessive arm flexion and abduction postures commonly observed in production lines, which over time can lead to discomfort, illness, and absenteeism.

The reduction in applied force with exoskeleton use was evident, as sEMG captured electrical signals in microvolts (μV) and revealed differences between conditions. The adjusted mean statistics for each evaluated muscle group highlighted modest differences between the use and non-use of the exoskeleton. However, participants’ perceptions of reduced subjective effort were clear.

The upper-limb exoskeleton can become an important ally for meat processing industries seeking to improve quality of life at work. However, other factors such as broad applicability, use by women, individuals with disabilities, and those with varied physical characteristics, must be explored to ensure inclusivity. Another potential area of study is the implementation of this technology as PPE, which would require further specific investigation for regulatory approval.