Estimating total maximum isometric force output of trunk and hip muscles after spinal cord injury

Med Biol Eng Comput, 2020 · DOI: 10.1007/s11517-020-02120-0 · Published: April 1, 2020

Spinal Cord Injury Neurology Biomechanics

Simple Explanation

This study focuses on improving the accuracy of musculoskeletal models used for designing controllers for functional neuromuscular stimulation (FNS) in individuals with spinal cord injury (SCI). These models rely on accurate estimates of maximum isometric force (MIF) of muscles. The current method of estimating MIF in SCI individuals often assumes it is 50% of able-bodied values, which may not be accurate. The study developed a method to estimate subject-specific MIF during dynamic motions produced by electrical stimulation. The findings suggest that the strengths of paralyzed muscles when stimulated with FNS may be underestimated, and using individualized estimates of MIF can improve the accuracy of musculoskeletal models.

Study Duration

Not specified

Participants

Five volunteers with SCI

Evidence Level

Not specified

Key Findings

1
Experiments indicate that an MIF of the 50% able-bodied values commonly used is significantly lower than the identified estimates in 33 of 44 muscle groups tested.
2
Subject-specific musculoskeletal models can more closely mimic the motions of subjects by using individualized estimates of MIF.
3
An estimate of 65% of the able-bodied value is much closer to matching the identified MIF values.

Research Summary

This study addresses the underestimation of maximum isometric force (MIF) in musculoskeletal models for individuals with spinal cord injury (SCI) using functional neuromuscular stimulation (FNS). A system identification method was used with a musculoskeletal model to estimate optimal MIF values by matching simulated and experimentally observed trunk motions in five SCI volunteers. The results suggest that commonly used 50% able-bodied MIF values underestimate actual force outputs, and individualized MIF estimates improve model accuracy, potentially accelerating controller design for neuroprostheses.

Practical Implications

Improved Controller Design

More accurate musculoskeletal models, incorporating individualized MIF estimates, will enable better design and tuning of controllers for FNS, reducing the need for extensive in-vivo testing.

Enhanced Neuroprosthesis Performance

By using more realistic models, the functionality and performance of implanted neuroprostheses for trunk control and seated posture can be significantly improved.

Personalized Rehabilitation Strategies

Subject-specific MIF estimates can be used to tailor rehabilitation strategies and FNS protocols to the individual's unique muscle characteristics and injury profile.

Study Limitations

1
The musculoskeletal model utilized in the system identification is based on the work of Lambrecht et al. [20], which has several assumptions that are also present in the current study.
2
Muscle fatigue was not accounted for within the model.
3
The users had a variable amount of time with the implant before the beginning of this study that ranged from 2 to 20 years.

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