Exo-LiFFT Simple Calculator

Exo-LiFFT: Ergo Assessment

Repetitions

lifts

Lever Arm

16 in

Object Weight

33.0 lb

Peak Load Moment

59 Nm

Exo Moment

Cumulative Damage Without Exo

0.014

Cumulative Damage With Exo

0.005

LBD Risk Without Exo

45.5

LBD Risk With Exo

33.4

Exo Reduces Cumulative Damage By

68.0 %

Beta Version 0.9
Exo-LiFFT is an ergonomics assessment tool to estimate the effect of lift-assist exoskeletons and exosuits on low back disorder (LBD) risk without EMG testing.

Reference: Zelik, K. E., Nurse, C. A., Schall Jr, M. C., Sesek, R. F., Marino, M. C., & Gallagher, S. (2021). An ergonomic assessment tool for evaluating the effect of back exoskeletons on injury risk. medRxiv.
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LBD (Low Back Disorder) Risk = probabiity of a job being a high risk job. High risk jobs are defined as 12+ injuries per 200,000 hours worked (Marras et al. 1993). Reductions in LBD Risk are correlated with reductions in actual low back injury incidence in the workplace, based on a multi-year prospective study (Marras et al., 2000).

Lever Arm = peak horizontal distance from lumbar spine to object during a lift.

Exo Moment = assistive lumbar moment provided by exo; obtained from exo manufacturer or empirical testing of device for specified task. Must be less than Peak Load Moment for Exo-LiFFT assessment.

For assessing multiple tasks, see the Exo-LiFFT Multi Task Calculator.

For more info on the original LiFFT ergonomics assessment tool, see Gallagher et al., 2017

Calculator is provided in the hope that it will be useful, but are provided "as is" without any warranty, express, implied or otherwise.

Questions/comments? Contact: karl.zelik@vanderbilt.edu

Exo Reduces LBD Risk By

26.6 %

Exo Reduces Back Muscle Loading By

43732 kg

Exo Reduces Handheld Weight By

51.0 %

Exo Reduces Handheld Weight By

7653 kg

Handheld Weight Lifted Without Exo

15000

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Example of how to use Exo-LiFFT calculator:

Imagine a safety professional has already implemented good ergonomic practices within the hierarchy of controls, to the extent practical. However, back discomfort and injuries persist amongst workers. They decide to evaluate the potential benefits of a commercially-available back exo that provides 30 Nm of torque about the back during a typical lift. In practice, this 30 Nm exo moment comes from mapping the lifting postures of workers (e.g., bend angles during lifting, as assessed by the safety professional) onto the mechanical assistance provided by an exo (e.g., back extension moment vs. joint angle curve provided by the exo manufacturer, or found from empirical testing of the device). If needed, contact the exo manufacturer to request exo moment values for relevant work tasks.

In this example, let’s say the safety professional already knows (from their previous ergonomic assessments, reviewing videos of work tasks, or from operational/organizational data) that their workers perform about 2,000 lifts per day, the average object lifted is 15 kg, and average horizontal distance from the spine to the object is about 50 cm. For this precursory analysis these values can be ballpark estimates, but note that the average peak exo moment (at or near the time of peak load moment) expected for a given job or task should be used, not simply the maximum moment an exo can generate.

Given this simple information, the safety professional can now use Exo-LiFFT to estimate the Cumulative Damage and LBD (Low Back Disorder) Risk to the workers with vs. without the exo, to quantify expected effects of augmenting workers with exos. The safety professional would simply input into the Exo-LiFFT Calculator:

Repetitions: 2000
Lever Arm: 50 cm
Object Weight: 15 kg
Exo Moment: 30 Nm

The Exo-LiFFT Calculator will compute the reductions in Cumulative Damage and LBD Risk with vs. without the exo.

See the manuscript for more details and examples.