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Ergonomic Assessment of Work Activities for an Industrial-oriented Wrist Exoskeleton

Roberto F. Pitzalis, Nicholas Cartocci, Christian Di Natali, Luigi Monica, Darwin G. Caldwell, Giovanni Berselli, Jesús Ortiz

TL;DR

Musculoskeletal disorders are a leading cause of work-related injuries; this study targets hand and wrist risk in artisanal saddle production. It combines subjective workload measures (NASA TLX), hand-wrist risk assessment (HAL/ACGIH TLV), and visual hand pain mapping with objective forearm EMG against MVC baselines to guide a wrist exoskeleton design, using metrics such as Normalized Peak Force ($NPF$). Findings reveal that workers report substantial fatigue while EMG measures indicate medium to high fatigue around the risk thresholds, highlighting the value of integrating subjective and objective data (normalized to $MVC$). The work provides a data-driven foundation for developing assistive devices in contexts where automation is impractical, aiming to reduce MSD incidence and improve worker health.

Abstract

Musculoskeletal disorders (MSD) are the most common cause of work-related injuries and lost production involving approximately 1.7 billion people worldwide and mainly affect low back (more than 50%) and upper limbs (more than 40%). It has a profound effect on both the workers affected and the company. This paper provides an ergonomic assessment of different work activities in a horse saddle-making company, involving 5 workers. This aim guides the design of a wrist exoskeleton to reduce the risk of musculoskeletal diseases wherever it is impossible to automate the production process. This evaluation is done either through subjective and objective measurement, respectively using questionnaires and by measurement of muscle activation with sEMG sensors.

Ergonomic Assessment of Work Activities for an Industrial-oriented Wrist Exoskeleton

TL;DR

Musculoskeletal disorders are a leading cause of work-related injuries; this study targets hand and wrist risk in artisanal saddle production. It combines subjective workload measures (NASA TLX), hand-wrist risk assessment (HAL/ACGIH TLV), and visual hand pain mapping with objective forearm EMG against MVC baselines to guide a wrist exoskeleton design, using metrics such as Normalized Peak Force (). Findings reveal that workers report substantial fatigue while EMG measures indicate medium to high fatigue around the risk thresholds, highlighting the value of integrating subjective and objective data (normalized to ). The work provides a data-driven foundation for developing assistive devices in contexts where automation is impractical, aiming to reduce MSD incidence and improve worker health.

Abstract

Musculoskeletal disorders (MSD) are the most common cause of work-related injuries and lost production involving approximately 1.7 billion people worldwide and mainly affect low back (more than 50%) and upper limbs (more than 40%). It has a profound effect on both the workers affected and the company. This paper provides an ergonomic assessment of different work activities in a horse saddle-making company, involving 5 workers. This aim guides the design of a wrist exoskeleton to reduce the risk of musculoskeletal diseases wherever it is impossible to automate the production process. This evaluation is done either through subjective and objective measurement, respectively using questionnaires and by measurement of muscle activation with sEMG sensors.

Paper Structure

This paper contains 5 sections, 3 figures.

Table of Contents

  1. Introduction
  2. Methodology
  3. Results
  4. Discussion
  5. Conclusions

Figures (3)

  • Figure 1: Working tasks assessed: seat preparation (a) and assembly (b), cushion covering (c), cushion mounting (d), and sewing (e).
  • Figure 2: NASA Task Load Index is divided into six subjective sub-scales (Mental Demand, Physical Demand, Temporal Demand, Performance, Effort, Frustration). These scales score perceived fatigue from "Very Low"(1) to "Very High" (21), except for "Performance", with which a task is performed, which is rated from "Perfect" (1) to "Failure" (21). In all cases lower values represents better scores.
  • Figure 3: HAL/ACGIH TLV assessment. The graph shows the maximum normalized force values (NPF) of 5 subjects exerted by the right hand and left hand while performing work activities, reporting both the old (2001) and updated (2018) threshold limits. White triangles report subjective (SUB) measures assessed by administering a CR-10 Borg scale to subjects; while black triangles report objective (OBJ) measures derived from an analysis of EMG data.