Manual materials handling (MMH) jobs can be tough. Working in factories, construction, labour, or anything involving prolonged/ repetitive lifting can lead to fatigue, discomfort, pain, and even injury when job tasks are poorly designed. However, even though an individual task might be OK, exposures on the body due to physical work accumulate, and a task that is normally OK can become problematic if performed after a series of other high exposure tasks. Therefore, it is important that ergonomists and injury prevention specialists are well equipped to understand these “multi-task” exposures and are aware of the tools that can measure them. Even the United States Council of Automotive Research (USCAR) Ergonomics Task Force (ETF), which encompasses research expertise across major US automotive companies, identified the need for ergonomists to be able to measure exposure accumulation across a workday, workweek, and beyond:
Despite the need for multi-task assessment, a recent survey (Beliveau et al., 2022) shows the prevalent use of “snap-shot” tools that only assess exposure at single instances in time (see the image below). While it is necessary to address seemingly obvious problems with a work task, such as extremely awkward postures as detected by a Rapid Upper Limb Assessment (RULA) or a Rapid Entire Body Assessment (REBA), this may cause us to overlook the accumulated volume of work performed by workers when consider a series of sequence of work tasks.
Recently, we tried to identify the state-of-the-art in multi-task assessment tools (Veerasammy et al., 2022 – you can download it for free!). For our purposes, we defined multi-task work as work that involves the completion of multiple efforts, done on the same workday, that result in an overall accumulation of physical exposure on the worker. We also aimed to understand and organize multi-task assessment tools based on how they aligned with underlying theories of musculoskeletal disorder causation. From a theory perspective, evidence suggests two primary pathways that can lead to musculoskeletal disorders (MSD) over time:
- through an accumulation of mechanical damage to loaded tissue, and/or
- through an accumulation of muscle fatigue.
Based on these two overall concepts, we identified tools and models that aligned with each primary pathway:
The diagram highlights several tools that can be used for multi-task assessment, and particularly those that focus on the accumulation of mechanical exposure pathway. However, some tools may be more accessible than others where accessibility and useability are often key factors that may influence tools use (Beliveau et al., 2022). For example, the Lifting Fatigue Failure Tool (LiFFT), The Shoulder Tool (TST), and the Distal Upper Extremity Tool, can all be freely and easily accessed through www.lifft.pythonanywhere.com, where basic training is also available via the website.
When thinking about the muscle fatigue accumulation pathway, several models exist within the peer reviewed literature, but very few accessible, usable tools. This may be related to our limited understanding of muscle fatigue, but perhaps more so, recovery. Emerging evidence suggests that not all recovery is equal, and in fact, recovery might depend on the muscles that were fatigued, but also on the motor units within the muscle that were fatigued (Potvin and Fuglevand, 2018).
Multi-task exposure accumulation and multi-task assessment tools to quantify exposure accumulation remain important. We found several tools that may be useful to estimate multi-task exposure accumulation for some tissues and modes of loading, but not all. We also found several models to predict the accumulation of muscle fatigue, but few tools ready for our ergonomics tool-belt. Our limited understanding of recovery from muscle fatigue may be one reason why few such tools exist. As MSD prevention efforts move forward, we continue to strive to develop and validate tools that can effectively quantify relevant risks (i.e., specific to the tissue, mode of loading, and exposure characteristics) in ways that are accessible and easy to use. Understanding how to optimize work to balance periods of effort with periods of recovery will help us to keep workers safe!
References
Beliveau, P.J., Johnston, H., Van Eerd, D., Fischer, S.L., 2022. Musculoskeletal disorder risk assessment tool use: A Canadian perspective. Appl. Ergon. 102, 103740. https://doi.org/10.1016/j.apergo.2022.103740
Potvin, J.R., Fuglevand, A.J., 2018. A motor unit-based model of muscle fatigue and recovery, in: Abstracts, Presentations, International Society of Electrophysiology and Kinesiology. International Society of Electrophysiology and Kinesiology, Dublin, Ireland, p. 144. [O18.4]. https://doi.org/10.1371/journal.pcbi.1005581
Veerasammy, S., Davidson, J.B., Fischer, S.L., 2022. Multi-task exposure assessment to infer musculoskeletal disorder risk: A scoping review of injury causation theories and tools available to assess exposures. Appl. Ergon. 102, 103766. https://doi.org/10.1016/j.apergo.2022.103766