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Model-based vs. measured muscle activity in dynamic lifting tasks with and without back-support exoskeletons.
Mohamad Behjati Ashtiani1, Mohammadhossein Akhavanfar2, Lingyu Li1
1Department of Industrial and Systems Engineering, Virginia Tech, Blacksburg, VA, USA.
Journal of Biomechanics
|November 16, 2025
Summary
Musculoskeletal models show promise for evaluating back-support exoskeletons (BSEs) by estimating muscle activity. While accurate, model predictions were less precise when participants wore BSEs during lifting tasks.
Area of Science:
- Biomechanics and Ergonomics
- Occupational Health and Safety
Background:
- Back-support exoskeletons (BSEs) aim to mitigate lower spine work-related musculoskeletal disorders.
- Surface electromyography (sEMG) is standard for assessing BSE effects but has practical limitations with trunk muscle monitoring.
- Musculoskeletal (MSK) models offer a non-invasive alternative for estimating muscle activity.
Purpose of the Study:
- To evaluate the accuracy of two MSK models (AnyBody™ Modeling System and OpenSim) in estimating trunk muscle activity.
- To compare model-derived muscle activity estimates against normalized sEMG (nEMG) data during lifting tasks with and without BSEs.
Main Methods:
- Two full-body MSK models (AMS and OpenSim) were used to estimate activity of lumbar extensors (longissimus, iliocostalis).
- Data were collected from 18 participants performing symmetric and asymmetric lifts with and without two types of BSEs.
- Model estimates were compared to nEMG using maximum normalized cross-correlation (MNCC), root-mean-square error (RMSE), and peak activity.
Main Results:
- Both AMS and OpenSim demonstrated strong correlations with nEMG (mean MNCC: 0.90-0.95) but showed moderate errors (mean RMSE: 0.09-0.15).
- Models generally captured reduced peak muscle activity with BSE use, aligning with nEMG findings, though magnitudes varied.
- Model accuracy decreased (lower MNCC, higher RMSE) under BSE conditions, indicating challenges with simplified human-BSE interaction models.
Conclusions:
- MSK models show potential for estimating trunk muscle activity in occupational settings and for evaluating BSE effectiveness.
- Accuracy is reduced in BSE conditions, highlighting the need for improved human-BSE interaction modeling.
- Findings support MSK model utility in ergonomics but emphasize the need for cautious interpretation, especially for complex scenarios.
