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Assessing the effects of a soft passive lowback exoskeleton for emergency medical services

Tiash Rana Mukherjee, Tiago Gunter, Eshan Manchanda,

Oshin Tyagi, Ranjana K. Mehta, Prabhakar Pagilla

4th IEEE International Conference on Human-Machine Systems

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Motivation

Emergency Medical Technicians and Paramedics (EMTs) Injuries in the US (2022)

22,781 injuries in EMS ¹

3 times national average of injuries across any work domain ¹
42% injuries lower back ^1,2
Main cause: Patient Handling and Lifting

2 million EMS → 22 millions patients/year ²

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Current mitigation strategies

Automatic Stretchers ^2,3
Trainings for better lifting strategies ^2,3,4

Injury rates are still high

Current solutions and techniques are not effective
Difficulties in designing strategies due to unstructured nature of EMS

Reference: 1. NIOSH (2022) ,2. Kim et al (2017) 3. Cole (2018) 4. Crill et al (2005)

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Ergonomic Solution

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Soft Passive Low back Exoskeletons (LBE) can be a potential solution.

“They are wearable devices that augment, enable, assist, or enhance motion, posture, or physical activity”

LBE use in manufacturing industries

Reduced muscular loads in lower back ^1,2
Changes in range of motion allowing more ergonomic lifting strategy ^3.4
Perceived physical exertion is lowered with LBE use for repetitive lifting and lowering tasks ³

Reference: 1. Goršič et al (2021) 2. Yandell et. al (2020) 3. Novak et. Al (2023) 4. Nuesslin et al (2023)

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Ergonomic Solution

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Soft Passive Low back Exoskeletons (LBE) can be a potential solution.

Research Objective:

Evaluate the neuromuscular, biomechanical, and subjective perceptions of Lowback exoskeleton use in Emergency Medical Service

Hypothesis

Reduction in muscular load in the lowback
Changes in ROM allowing efficient utilization of legs during lifting tasks
EMTs will perceive lowered physical and mental demands

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What did we do?

Experimental Protocol

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Participant wearing the Hero Wear Back Assist Exosuit

Tasks selected based on EMT specific Physical Agility Tasks (PAT)

Control and Exo conditions counterbalanced.

Repeated twice in each condition. All EMTs did both conditions.

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For our experiment: We used a commercially available exo as shown in the picture, next

(click)

We selected five tasks taken from the PAT test that new EMT recruits undergo to be deemed physically fit for the occupational demands. These tasks were performed in a circuit to mimic real world applications. All EMTs were asked to perform the tasks they way they would on field. – they started and ended at the same task- that was the backboard lift. The other tasks in order were – a one hand carry of a cardiac monitor across the stair case, a barbell carry emulating stretcher carry, stretcher push/pull into the ambulance and CPR. These tasks are commonly performed on the field and With this experiment we wanted to test if the exoskeleton was benefitting or being detrimental to during use

(click)

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What did we do?

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Number of participants: 20

Average Age (SD):
Average BMI (SD):
Average Years of experience (SD): 10 (5.6)

Statistical Analysis performed using Wilcoxon's Signed Rank Test b/w conditions (control, exo)

Anterior Deltoids

Upper Trapezius

Lumbar Erector Spinae

Biceps Femoris

Metrics: Amplitude Probability Density Function

Mean (50^th percentile)
Peak (90^th percentile)
Reference Task: Symmetrical Ankle to Overhead Lifting with a 9.8 kg cardiac monitor

Dependent Variables:

Muscle Activity

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What did we do?

Statistical Analysis performed using Wilcoxon's Signed Rank Test b/w conditions (control, exo)

Head
Shoulder
Elbow
Wrist

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Dependent Variables:

Muscle Activity

Range of Motion

Formula ROM = Joint Angle (95^th Percentile – 5^th Percentile)

Number of participants: 20

Average Age (SD):
Average BMI (SD):
Average Years of experience (SD): 10 (5.6)

L5/S1
Hip
Knee
Ankle

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What did we do?

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Dependent Variables:

Muscle Activity

Range of Motion

Ratings of perceived exertion
Mental Demand
NASA - TLX

Participant

Researcher

Participant performing Backboard Lifting task

Collected after trials in each condition were completed.

Statistical Analysis performed using Wilcoxon's Signed Rank Test b/w conditions (control, exo)

Number of participants: 20

Average Age (SD):
Average BMI (SD):
Average Years of experience (SD): 10 (5.6)

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Results!

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Electromyography

Benefits observed in lower limbs

Lowered muscular demand seen in left side (19 EMTs - right dominant)

Weight transfer to non-dominant leg provides stability ^1-3
LBE use offloaded weight from the left limb

Benefits seen in squat lifting, staircase climbing and on-floor CPR

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Reference: 1. Yoo et. al (2012) 2. Tanaka et. al (1984) 3. Oda et. al (1995) 4. Lyon et. al (1983) 5. Ho et. al (2018)

Muscle Activity comparable between conditions for low back

Deviates prior studies evaluating LBE

Where, LBE use decreases spinal loads therefore decreases muscular load in the lower back

Exoskeleton use did not affect low back or shoulder

EMTs knew movement kinematics – already used their legs more than the lowback

With LBE use - Red: ↑ Green:↓

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Motion Capture

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Reference: 1. Yoo et. al (2012) 2. Tanaka et. al (1984) 3. Oda et. al (1995) 4. Lyon et. al (1983) 5. Ho et. al (2018)

Enabled different postural strategies

~40% ↑ Hip Adduction, ~37% ↓ Knee Rotation, ~10% ↑ Ankle Flexion

No differences observed during lifting tasks
Potentially contributing to Limb Stability during stair climbing tasks

Causing improved load redistribution in the Biceps Femoris⁴

~12% ↓ Knee Rotation & Adduction during CPR

CPR requires effective upper body weight during chest com⁵

Reduced ROM enabled an improved upright position during kneeling

With LBE use - Red: ↑ Green:↓

One-Hand Carry

Barbell Carry

CPR

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So here, our second hypothesis was we expected changes in the ROM of the lower extremity based on Exo use in manufacturing industry.

For example an increased ROM for the knees and reduced trunk and hip ROM in lifting and lowering tasks are likely beneficial which means that participants lifted more with their legs, But in our case we do not observe differences in any ROM during the Backboard lift that is a similar task. And this in our opinion is good because the exo did not impede the correct way of lifting.

(click)

But if we look at the staircase climbing tasks, especially the barbell carry where they had to carry a 75 pound barbell across the staircase and then return walking backward, we can say the the decrease in the knee rotation and increased ankle rotation might be to improve limb stability for better postural control. And this might have caused redistribution of load engaging the right limbs too as seen in the muscle activity.

(click)

Similarly, we observed some differences in posture during CPR

With keeping the knees closer during kneeling and this might have beneficial for effective use of upper body weight during chest compression. So from the discussed results we can say that the exo was probably beneficial – but we also know that these benefits were dependent on the context of the tasks and it cannot be generalized.

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Perception

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Despite comparable ratings of RPE and MD, users report lower ratings of perceived workload with exoskeleton use

Aligns with no differences observed in muscle activity of lower back
But suggests a mismatch between effort assessments during individual tasks and after circuit completion

With LBE use - Red: ↑ Green:↓

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Limitations & Future Work

Current study focused only on Range of Motion and Muscle Activity ^4-6

Is the LBE use enhancing task performance?
Did EMTs adopt different postural strategies to accommodate similar levels of performance?

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Immediate benefits not recognized is a concern ¹

This can affect user’s willingness to adopt LBEs
Need to investigate user perception and perspectives

Sex differences might influence HEI ^2-4

Studies evaluating LBEs have reported significant sex differences
Particularly due to sex-based differences in human physiology

Reference: 1. Mun et. al (2006) 2. Bennet et. al (2023) 3. Gorsic et. al (2021) 4. Bennet (2022) 5. Ojelade et. al (2023) 6. Kim et. al (2024)

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Although our results from this study provide a fundamental understanding of how EXOs might impact EMTs when they are used in practice. There are still several limitations that we plan to address in the future.

First, just as I said initial interaction differs from future assessments. This is a concern as not recognizing immediate benefits affect technology acceptance adversely. So we propose more indepth behavioral assessments or even a neuroergonomic approach where we look at the brain data in tandem to other measures. I am a part of the neuroegonomics laboratory – and we use ambulatory neuroimaging techniques to look at how functionally independent regions of the brain interact with each other. In some of our previous studies, brain data has helped us understand certain perceptual results that surveys weren’t able to pin point at. However, due to methodological constrains we could not collect the brain data here – but for future studies we aim to collect it.

Second, the participants were mostly males. Due to differences in physiology of different sex there are significant differences in the way they interact with the device. Infact, one of my prior work with passive shoulder exoskeletons have found that the exo was benefiting females more – infact it was more of an equalizing factor. Therefore, future studies should definitely approach human-exoskeleton interaction with more sex-balanced populations.

Lastly, I have been saying oh exo was beneficial – we still don’t know what we are assuming to be a benefit, if is maybe increasing the risk somewhere else. Therefore from this study we do understand that effects of exo use need to be evaluated using task-specific metrics, but in future we wlll also assess the quality of performance and will try to perform risk-based assessments for a more comprehensive evaluation.

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Thank you!

Connect with us!

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Advanced Robotics Laboratory at Texas A&M:

https://robotics.engr.tamu.edu/

Neuroergonomics Laboratory at

University of Wisconsin – Madison:

https://neuroergolab.org/

Tiash Rana Mukherjee:

tiashrana@tamu.edu

LinkedIn: ./tiashranamukherjee

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