Ergonomics of stretching

Responding are Josh Kerst, vice president, and Michael Hoonhorst, associate consultant and ergonomics engineer, Humantech Inc., Ann Arbor, MI.

Answer: To stretch or not to stretch? This is a common question within the ergonomics community. Should companies deploy stretching programs to reduce the likelihood of employees developing a work-related musculoskeletal disorder? Although many companies advocate stretching before and during the workday, research indicates mixed results. Some research that claims stretching is effective is based on subjective, rather than objective, measurements. Therefore, these claims aren’t necessarily proven.

MSDs are injuries that usually occur at joints in the body and involve muscles, bones, nerves, tendons, ligaments, cartilage and spinal discs. They may be the result of overexertion and cumulative load on the body. Proponents of stretching argue that it limits the risk of developing these types of injuries because it alters the properties of the tendon muscle unit, changing the amount of force production and range of motion at that particular joint. This change affects the distance the muscle can stretch and the amount of force required to tear the tissue.

However, the largest body of research is focused on athletes and injury prevention. Care should be taken in extrapolating these findings to workers, as the intensity, repetition and duration of physical exertion vary between these two populations. In most cases, major physiological differences between athletes and industrial workers make inference even more difficult.

Reviews of the most relevant published medical studies on stretching found that while stretching does increase flexibility, it does not prevent injuries.¹ Dr. Ian Shrier, past-president of the Canadian Academy of Sport and Exercise Medicine, agrees with these findings.

His research concluded that stretching will not change eccentric muscle activity, which is believed to contribute to most injuries, and that stretching actually can cause skeletal damage. Research also suggests that stretching may mask muscle pain, which could cause the worker to ignore key pre-injury signals.

Bruno and Vieira² reviewed seven articles that measured the ability of a stretching program to prevent work-related MSDs. The articles looked at workplace stretching programs across several industries. None of the articles reviewed showed a significant decrease in work-related MSDs.

Researchers have expressed concern that stretching may be harmful for those already experiencing work-related MSD symptoms. The article, “A review of physical exercises recommended for VDT operators,” pointed out that 90 percent of common office ergonomics stretching exercises could actually aggravate pre-existing conditions.³

Findings from Humantech’s recent studies show that companies saw better returns on their investments by proactively fitting the job to the person, rather than seeking to match the person to the demands of the job.

The participating companies understand that they should drive improved employee performance through ergonomics, rather than attempting to manage MSDs. For example, if a person complains of back pain because he or she constantly bends over to retrieve parts from a pallet, raise the height of the pallet. The higher work height will eliminate the need to bend over and the associated back pain.

If we can perform our work in the comfort zone (between our shoulders and knees), then our need to stretch out aches and pains brought on by our job tasks diminishes.

References
1. Thacker, S.B., Gilchrist, J., Stroup, D.F., and Kimsey, C.D. (2004). The impact of stretching on sports injury risk: a systematic review of the literature. Medicine & Science in Sports & Exercise, Vol. 36, No. 3, pp. 371-378.
2. Bruno, R.C. and Vieira, E.R. (2008). Stretching to reduce work-related musculoskeletal disorders: A systematic review. Journal of Rehabilitation Medicine, Vol. 40, No. 5, pp. 321-328.
3. Lee, K., et al. (1992). A review of physical exercises recommended for VDT operators. Applied Ergonomics, Vol. 23, No. 6, pp. 387-408.

Editor’s Note: This article represents the independent views of the author and should not be construed as National Safety Council endorsements.