The DOL Strength Levels – does oversimplifying job demands increase exposure to injury risk?

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Written by: Mike Sonne, PhD, CCPE

Summary: The DOL strength levels classify jobs into 5 separate categories defined by force/weight, and frequency of exertion. The classification system leads to a broad oversimplification of the demands of work, which in the worst case can lead to over and under estimates of physical demands of over 500%. A much more granular system is needed to better understand the different physical demands of work, and how that  can be used in return to work, and injury prevention.

The Department of Labor’s strength definitions are widely used when determining the physical demands of a job, or the capacity of a worker when it comes to post-offer of employment testing,  return to work, disability management, and functional capacity evaluations. These strength definitions aim to look at the material handling component of jobs, and state what is required of the worker to be able to successfully perform that aspect of the work. Strength demands of work are broken into 5 categories – sedentary, light, medium, heavy, and very heavy. Each of these demand levels have a force and frequency component – stating what weight a person can lift, push, pull, or carry at a given frequency (Table 1).

Table 1. Force/Weight, and frequency characteristics for the DOL levels of Sedentary through Very Heavy.

Rating Occasionally Frequently Constantly
Sedentary 0 – 10 lbs 0 lbs N/A
Light 0 – 20 lbs 0 – 10 lbs 0 lbs
Medium 20 – 50 lbs 10 – 25 lbs 0 – 10 lbs
Heavy 50 – 100 lbs 25 – 50 lbs 10 – 20 lbs
Very Heavy 100+ lbs 50+ lbs 20+ lbs

According to the Bureau of Labor Statistics, the most common jobs in America are in the medium category – but this varies greatly by industry. Management and technical jobs have more of the light jobs, whereas construction, trades, and manufacturing jobs have more of the heavy jobs (Figure 1).

Figure 1. Percentage of civilian jobs requiring different strength levels in selected occupations, Bureau of Labor Statistics, 2016.


While these five levels of classification of strength are useful in providing an initial look at the demands of work, there is not a lot of granularity when it comes to establishing how a worker is capable of performing these tasks.

Ergonomists have a wide variety of tools for assessing the demands of work, and many are specific to individual physical demand types. One of these tools is the NIOSH lifting equation (Waters et al., 1991) – a tool that looks at the start and end height of a lift, the frequency and duration of lifting, the twisting required, and how far the worker has to reach to perform the lift. This equation returns a recommended weight limit (RWL) – the amount of weight that could be lifted that would keep the worker’s back safe during work. If you divide the actual weight being lifted by the RWL, you will get a value indicating the overall risk level of that given lift. If that value is greater than 1.0, this lift is above the RWL and puts the worker at a higher risk of injury.

Looking at the DOL levels, and a simple lift from about knee height to waist height, I simulated what the RWL would be for the ranges of frequencies and lifting weights from the DOL strength levels (Figure 2). (For those who would like to replicate these calculations, the start height was 30 cm, travel distance was 45 cm, horizontal reach was 40 cm, there was no asymmetry, or coupling factors modification. For frequencies, I used the less than 1 hour factors, and V<30. Each lift was assumed to be 2 s in duration, and the corresponding FM factor was found).

Figure 2. Lifting Index for the minimum, average, and maximum frequency possible (in % of time) for each DOL strength level. Values of greater than 1 (above the black line), would be considered “unacceptable”, as they increase the risk of injury in the lifter.

According to the Lifting Index, and the NIOSH lifting equation, the vast majority of DOL levels for strength would be unacceptable and cause an elevated risk of injury for workers. In fact, no simulated task for the heavy or very heavy categories would be a safe lift, and only 2 of the 15 simulated lifts in the medium category would be safe lifts. What is very interesting, is these large ranges spanning the frequencies identified in the DOL strength levels, can produce a lifting index of as low as 0.87, and as high as 4.41, all within the same strength bin (in this case, Medium). That is a 507% increased risk of injury in one strength category – primarily because of the high force levels, and huge variety of frequencies defined in this methodology.

The NIOSH lifting equation examines risk during lifting as a factor of the amount of spine compression that is occurring. NIOSH recommends lifts should not exceed 3400 N of spine compression during lifting. The peak spine compression of a lift is an interesting variable to examine, but it doesn’t necessarily factor in frequency – which can be an important variable in assessing risk. Even without frequency, you can see the DOL levels and their corresponding peak spine compression levels (predicted using Potvin 1997’s method) often exceed what’s known to be safe (Figure 3).

Figure 3. Predicted spine compression level from different lifts, classified by the DOL levels of strength, compared to the NIOSH safe lifting limit of 3400 N.

DOL levels that feature 50 lbs or higher as the acceptable lift are in the high risk category. That means, these types of jobs are only appropriate for very strong individuals, if you want someone to work there with a low risk of injury. Even then, over the long term, these individuals are more likely to sustain a back injury in the workplace.

What isn’t included in the DOL levels  are the other physical demands that could lead to an increased risk of injury in these types of work, e.g. lifting at, or above, shoulder height; lifting with a flexed spine; or a poor point of contact for gripping significantly impact the risk of injury.

The Demand Score includes the physical demands included with strength, but also factors in reaching, gripping, handling, data entry, and many more (26 different physical demands),  compares these demands against known ergonomic standards, and develops a score from 1 to 100, helping you better understand a job, and how it compares to other jobs within the same industry.

In summary – job descriptions and physical demands analyses are very nuanced and detailed things. Boiling them down into one of 5 categories over-simplifies the different factors in return to work and injury prevention, which can lead to either prolonged absences, or exposure to higher levels of injury risk than previously considered.

Our Solution

MyAbilities has included the strengths points of the DOL levels for exertions, but build out these other risk factors into a more comprehensive look at a job called the Demand Score.

MyAbilities has 30,000 Job templates in JOBX system, and each job has a demand score. For each of those jobs, you’re not fitting them into one of 5 categories – you’re fitting them in to that 100 point grade, allowing for much finer determination on return to work capacity and identification of modified or light duty jobs.

About Dr. Michael Sonne

VP Innovations and Research at MyAbilities

A leading occupational biomechanics researcher, with a history of developing technologies to automate ineffective processes in the ergonomics industry. In 2010, Mike developed the Rapid Office Strain Assessment – a method for conducting self-guided, office ergonomics assessments, resulting in a reduction of musculoskeletal injuries. Mike has developed global standards for muscle fatigue assessment in repetitive work, particularly in assembly lines. Mike is an adjunct professor at Brock University, and the University of Ontario Institute of Technology, and continues to publish in peer reviewed journals.


Waters, T. R., Putz-Anderson, V., Garg, A., & Fine, L. J. (1993). Revised NIOSH equation for the design and evaluation of manual lifting tasks. Ergonomics, 36(7), 749-776

Potvin, J. R. (1997). Use of NIOSH equation inputs to calculate lumbosacral compression forces. Ergonomics40(7), 691-707

Use Collaboration, Technology for ADA Compliance and Positive Return to Work Outcomes

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May 28, 2019 BY AMAXX / Michael B. Stack

Returning an injured worker to the job before he’s physically ready can be a nightmare. The last thing an employer wants to do is put the employee at risk of reinjury.

On the other hand, waiting to bring an employee back until he is 100 percent recovered prolongs the number of lost work days and impedes the worker’s recovery. Reinjuries, as well as extended disability durations both, add costs to the claim.

What’s needed is an accurate depiction of the physical requirements of a job, along with a deep understanding of exactly what the injured worker is physically able to do or not do. Armed with such information, the employer can make the best decisions for the injured worker and the organization.


Video Kinematics Produces Physical Job Demand Descriptions on Steroids

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March 26, 2019 BY AMAXX / Michael B. Stack

How familiar are you with the physical demands of every job in your company? That may sound like a loaded question, but the more understanding you have of each job, the better you’ll be at preventing injuries, reducing workers’ compensation costs and improving your bottom line.

However, many companies face the challenge of lack of time or resources to do a thorough and complete job of developing a physical demands database. The development of technology and artificial intelligence now makes this easy.


The MyAbilities Digital Job Profile

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Hi everyone! We’re looking to get some feedback on our new format for conducting physical demands descriptions. We have a short survey here – the only caveat is that you’ll need a modern web browser to complete it (anything but Internet Explorer 11).

Preventing Repetitive Strain

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4.5 million Canadian adults annually experience a Repetitive Strain Injury that is serious enough to limit normal, day-to-day activities, and with Repetitive Strain Injury Awareness Day is coming up on Thursday, February 28th, we welcome Dr. Mike Sonne to the show to help us prepare.

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Recalculating for Small Business – Reed Hanoun & Paul Bellantone

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How to adjust your workspace to reduce the risk of injury

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JANUARY 22, 2019 BY CityNews

Small inexpensive adjustments you can make to your workspace to increase blood flow and reduce the risk of injury.

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Work Habits Impact Bodies

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Many do not realize the impact work habits have on their physical bodies with incorrectly placed or improperly sized equipment causing injuries which can result in time off work, depending on insurance and benefits, and could mean lost wages, says Reed Hanoun, founder and CEO of MyAbilities. It works with employers, service providers, and insurers to keep people safe and healthy in their workplace environment. Its technology uses ergonomic research to conduct self-assessments and provide self-guided training to make sustainable office ergonomic changes. However, injuries can be prevented. Office chairs are adjustable for a reason. The best chairs allow for frequent adjustments, changing posture throughout the day. This promotes healthy blood flow and reduces the effects of muscle fatigue. Those who work primarily on a laptop, tablet, or a cell phone should realize these devices were not developed with a 40-hour work week in mind. Employees should consider getting a full-sized keyboard, a monitor, and mouse to plug in. Finally, employees should rest to destress. When people get stressed, muscles become tense, and back pain and other musculoskeletal discomfort can result. Microbreaks should be taken throughout the day to work on deep breathing and to stretch.

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ODG by MCG Announces Release of ODG Job Profiler Powered by MyAbilities

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Austin, TX – ODG, an MCG Health company, recently announced a partnership with MyAbilities Technologies to incorporate a unique new product option, the ODG Job Profiler, into its industry-leading medical treatment and return-to-work (RTW) guidelines.

The ODG Job Profiler is a software platform powered by MyAbilities™ which will be made available as an add-on to the ODG by MCG User Interface in January 2019. The ODG Job Profiler adds job demand data across every industry and occupation by providing a comprehensive database of physical, cognitive, and environmental demands specific to over 30,000 jobs spanning nearly every industry. This solution helps insurers, third-party administrators (TPAs), and employers identify and mitigate the risk of injury by creating a customized Physical Demands Analysis (PDA) for each job function, adjusting disability duration guidelines according to job demands.


MyAbilities Helping Companies Stay Ahead of the Curve

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New Burlington health and safety technology company introduces artificial intelligence in the workplace

Nov 22, 2018, Burlington Post

MyAbilities is a health and safety technology company that incorporates artificial intelligence (AI) and advanced data analytics. – MyAbilities photo

When it comes to analysis of ergonomic trends and assessing physical demands, MyAbilities is helping companies stay current and competitive.

The new Burlington-based business has developed an integrated ergonomic innovation that positions artificial intelligence as a digital assistant.

“We wanted to create an advanced solution that strives for objectivity and accuracy,” said founder and CEO Reed Hanoun. “Utilizing artificial intelligence to track physical job demands, our technology allows employers to reduce occupational risk and streamline services in real time.”