The Importance of Lifting in Function

Proper body mechanics are critical to maintaining musculoskeletal health and preventing injuries, especially during lifting tasks. Lifting is a fundamental activity both at work and at home—from moving boxes in a warehouse to carrying groceries or picking up children. When performed incorrectly, lifting can lead to common injuries such as low back pain, shoulder strain, and overuse disorders.

Work-related musculoskeletal injuries are a significant concern, accounting for a substantial portion of lost workdays and healthcare costs annually. These injuries not only affect a worker’s productivity but also their quality of life. Physical therapists (PTs) play a key role in addressing these issues by:

• Assessing Faulty Movement Patterns: PTs evaluate how individuals perform lifting tasks and identify compensatory patterns, such as excessive spinal flexion, poor engagement of core stabilizers, or overuse of smaller muscle groups like the shoulders. By observing movement mechanics, PTs can pinpoint areas of dysfunction and develop strategies to correct these patterns, such as improving coordination and ensuring appropriate muscle activation during lifting.

• Strengthening Key Muscle Groups: Proper lifting relies on a combination of strength and stability in these critical areas and others. PTs primarily focus on:

  • Core Muscles: Enhancing core stability to protect the spine and improve force transfer.

  • Lower Body: Strengthening the glutes and quadriceps to drive power during lifts.

  • Shoulders and Upper Back: Building scapular stability and rotator cuff strength to manage load and prevent shoulder injuries.

  • Eccentric Control: Developing hamstring and lumbar extensor strength to control lifting descent and protect against strain.

• Educating Patients on Optimal Biomechanics: PTs guide patients in practicing proper lifting techniques, such as maintaining a neutral spine, engaging the core, using the legs to lift rather than the back, and keeping the load close to the body. Repeated practice and education foster safer habits, reducing the likelihood of reinjury.

By proactively addressing ergonomic risks, PTs can help employers reduce injury rates and improve worker safety. Through targeted interventions, PTs can help patients and workers perform daily tasks safely and efficiently, reducing the overall burden of work-related injuries.

A Practical Way to Evaluate a Lift-The WISHA Calculator

The WISHA Lifting Calculator offers a standardized and evidence-based approach to evaluating and quantifying the safety of lifting tasks. This tool is invaluable for physical therapists aiming to assess lifting risks and guide interventions effectively. By incorporating the WISHA Calculator into practice, PTs can:

• Objectively measure the risk associated with specific lifting tasks.

• Provide evidence-based recommendations for safer lifting practices.

• Educate patients and employers on the biomechanics of lifting to prevent injuries.

Understanding the WISHA Calculator: Inputs and Outputs ¹

The WISHA Lifting Calculator evaluates lifting tasks by analyzing key factors:

• Weight of the load: The heavier the load, the higher the risk.

• Horizontal and vertical position of the load: Determines the distance from the body and the strain placed on the spine.

• Distance from the body: Lifting objects closer to the body reduces mechanical stress.

• Lifting frequency and duration: Repetitive or prolonged lifting increases fatigue and injury risk.

• Twisting or awkward postures: These movements exacerbate strain and injury potential.

Based on these inputs, the calculator generates outputs that help assess the risk of injury¹ :

• Recommended Weight Limit (RWL): The RWL represents the maximum safe weight for a specific lifting task under the given conditions. It is calculated by considering the load’s position, distance from the body, and frequency. Adjustments are made for factors like twisting or awkward postures, which can increase strain and reduce safe limits.

• Lifting Index (LI): The LI is a ratio of the actual weight lifted to the RWL. An LI below 1 indicates that the task is within safe limits, while an LI above 1 suggests the lift exceeds safety thresholds and poses a higher risk of injury. For example, an LI of 1.5 indicates the task is 50% more demanding than the recommended limit.

• Twisting Adjustments: The tool calculates a reduction in the RWL when significant twisting or rotation is involved in the lift. This adjustment reflects the additional strain placed on the spine and surrounding structures during asymmetrical movements.

• Frequency Multipliers: The output includes adjustments based on how often the lift is performed. High-frequency lifting tasks result in a lower RWL due to cumulative fatigue and increased injury risk.

• Visualization Tools: The calculator provides graphical representations or charts that outline the risk factors, including the relationship between load weight, posture, and frequency. These visuals are helpful for explaining risks and recommendations to patients and employers.

Validating the WISHA Lifting Calculator

The WISHA Lifting Calculator is often compared to the Revised NIOSH Lifting Equation (RNLE), a well-established ergonomic assessment tool used to determine safe lifting limits based on biomechanical and physiological factors. The RNLE considers variables such as horizontal reach, vertical lift, frequency, duration, and asymmetry to calculate a Recommended Weight Limit (RWL) and Lifting Index (LI). While comprehensive, the RNLE can be complex and time-consuming to apply in fast-paced clinical and occupational settings.

A study titled "A Comparative Assessment of Manual Load Lifting Using NIOSH Equation and WISHA Index Methods in Industrial Workers of Shiraz City" examined the validity of the WISHA Lifting Calculator by comparing its results to the RNLE. The study found a fair correlation between the two methods, supporting WISHA’s reliability as a tool for ergonomic risk assessment. While the RNLE remains the gold standard for detailed lifting analysis, the WISHA Calculator's simplicity makes it highly practical for quick evaluations in clinical and workplace environments.

The study highlighted that while the RNLE provides a more detailed breakdown of lifting risk, the WISHA Lifting Calculator is much easier to administer. Its user-friendly format allows for efficient screening of high-risk lifting tasks, making it ideal for use by physical therapists in clinical settings, occupational safety professionals, and employers seeking to implement ergonomic improvements. The findings reinforce that the WISHA Lifting Calculator is a valid and effective tool for assessing work-related lifting risks and recommending modifications to prevent musculoskeletal injuries.

Patient Case Study

Let’s practice here and see the utility of a calculator. Below is a patient case study and the patient has a job requiring lots of routine lifting. As you go along the case please also utilize this online resource that does a great job of breaking down how to do the calculations to understand his injury risk:
https://www.slideshare.net/slideshow/wisha-lifting-calculator/70922215#24 

John is a 35-year-old warehouse employee responsible for stocking shelves. His daily tasks involve lifting boxes from the floor and placing them onto shelves at various heights. Each box weighs approximately 30 pounds. He performs this lifting task about 10 times per hour, totaling 80 lifts during his 8-hour shift.

Lifting Task Details:

• Load Weight: 30 pounds

• Horizontal Distance: 20 inches (distance from the midpoint between the ankles to the hands while lifting)

• Vertical Position:

  • Start: 10 inches from the floor

  • End: 50 inches from the floor

• Asymmetry Angle: 0 degrees (no twisting involved)

• Frequency: 10 lifts per hour

• Duration: 8 hours per day

Take a brief pause here and try and apply what you have already learned previously to get an idea about the safety of this lifting task for John. Hint: utilize the lifting index calculation. 

Results:

• Recommended Weight Limit (RWL): 25 pounds

• Lifting Index (LI): 1.2 (calculated as Actual Load Weight / RWL, i.e., 30 lbs / 25 lbs)

For those interested in the numbers breakdown here is what I have.

Calculation Steps:

1. Unadjusted Weight Limit (UWL):

   • Based on the vertical position of the hands at the start of the lift (10 inches from the floor), the UWL is determined.

   • According to the WISHA Lifting Calculator, for a vertical height of 10 inches, the UWL is 40 pounds.

2. Adjustment Factors:

   • Horizontal Location Adjustment:

     • For a horizontal distance of 20 inches, the adjustment factor is 0.85.

   • Frequency and Duration Adjustment:

     • For a frequency of 10 lifts per hour over an 8-hour shift, the adjustment factor is 0.75.

   • Twisting Adjustment:

     • Since there is no twisting involved (0 degrees), the adjustment factor is 1.0.

3. Calculate the Adjusted Weight Limit:

   • Adjusted Weight Limit = UWL × Horizontal Adjustment × Frequency/Duration Adjustment × Twisting Adjustment

   • Adjusted Weight Limit = 40 lbs × 0.85 × 0.75 × 1.0

   • Adjusted Weight Limit = 25.5 pounds

4. Determine the Lifting Index (LI):

   • LI = Actual Load Weight / Adjusted Weight Limit

   • LI = 30 lbs / 25.5 lbs

   • LI ≈ 1.18

An LI of 1.2 indicates that the current lifting task exceeds the recommended safe limit, suggesting an increased risk of musculoskeletal injury.

Alright, great. Now that we understand the lifting task has an increased likelihood of causing injury what are some practical recommendations we can make for John? Obviously, we are not going to ask him to change jobs because that’s not practical for 99% of patients. Instead we are gonna play with the numbers. If you understand the inputs of the calculator it’s easy to change outputs.

Practical Recommendations for Risk Mitigation:

• Reduce Load Weight: Decrease the weight of each box to 25 pounds or less to align with the RWL.

• Adjust Shelving Heights: Modify shelf heights to minimize vertical lifting distance, ideally keeping lifts between knee and shoulder height.

• Increase Team Lifting: Encourage team lifting for heavier items to distribute the load.

• Implement Mechanical Aids: Use lifting aids or equipment to reduce manual handling.

• Provide Training: Educate workers on proper lifting techniques and the importance of ergonomics. This is where our expertise of biomechanics really comes in.

These changes are not rocket science and that’s a good thing. Improving the safety and efficiency of everyday tasks has a far greater impact on our patients' long-term health than an often-overlooked home exercise program focused on core stability.

Practice Uses in Clinical Settings

The WISHA Lifting Calculator serves as a valuable tool in occupational health for:

• Job Modification: Providing objective data to support changes in job design or work practices to enhance safety.

• Workers' Compensation Cases: Offering quantifiable evidence of lifting risks, which can be instrumental in assessing injury claims and determining necessary workplace adjustments.

By utilizing the WISHA Lifting Calculator, physical therapists can proactively identify high-risk lifting tasks and implement evidence-based interventions to prevent injuries, thereby promoting a safer and more efficient workplace.

Parting Thoughts

The WISHA Lifting Calculator serves as a valuable, evidence-based tool for assessing and mitigating lifting risks. By integrating this calculator into practice, physical therapists can improve workplace safety, prevent injuries, and advocate for necessary ergonomic adjustments. Its simplicity and ease of use make it a highly practical resource for clinical settings, ensuring that risk assessments can be performed quickly and effectively without requiring extensive calculations.

Also would love to hear any other thoughts on the patient case. How would you approach modifying the lifting tasks of our warehouse worker case study? What strategies would you implement to reduce their lifting burden? Share your insights and experiences in the comments, and let’s continue the conversation on improving workplace ergonomics together!

References:

1. ErgoPlus. WISHA Lifting Calculator Guide. ErgoPlus website. Available at: https://ergo-plus.com/wisha-lifting-calculator-guide/. Accessed February 1, 2025.

2. Asadi N, Choobineh AR, Keshavarzi S, Daneshmandi H. A Comparative Assessment of Manual Load Lifting Using NIOSH Equation and WISHA Index Methods in Industrial Workers of Shiraz City. J Health Sci Surveillance Sys. 2015;3(1):8-12.

3. Washington State Department of Labor and Industries. WISHA Lifting Calculator. SlideShare, uploaded by SlideShare user, 2017, https://www.slideshare.net/slideshow/wisha-lifting-calculator/70922215#24. Accessed 2 Feb. 2025.

Disclaimer:

I am a current Doctor of Physical Therapy (DPT) student sharing information based on my formal education and independent studies. The content presented in this newsletter is intended for informational and educational purposes only and should not be considered professional medical advice. While I strive to provide accurate and up-to-date information, my knowledge is based on my current academic and clinical rotations and ongoing learning, not extensive clinical practice.