From The Ergoweb® Learning Center

Research Summaries: Workstyle and Upper-Extremity Symptoms; and, Pathomechanics of Peripheral Nerve Loading

It’s Not What Is Done But How It’s Done

Key Point: Employee response to physical risk factors and work demands is a better predictor of musculoskeletal symptoms than job stress factors.

Workstyle – the psychological, physiological, and behavioral response to work demands and physical risk factors – predicted upper extremity pain and functional limitation among 169 office workers in a prospective study by Nicholas et al. The authors suggest that exposure to physical risk factors and high/increased workload can create negative employee workstyle response (i.e., self-imposed workpace/workload, breaks, and mood) which contributes to the development/exacerbation of upper extremity disorders.

Subjects, some with and some without upper extremity symptoms, completed a baseline self-reporting survey consisting of inquires related to:
* Sociodemographics and work history
* Work demands (workload and workload variability measures)
* Job stress (work-related conflicts, pace of work, physical conditions)
* Ergonomic factors (physical work factors and Borg scale of perceived exertion)
* Workstyle measure (working through pain, social reactivity, limited workplace support, deadlines/pressure, self-imposed workpace/workload, breaks, mood, and autonomic response)

After three months, the participants filled out a survey involving work-related health and functional capability. Cases were those that 1) had upper extremity symptoms within the prior 12 months, 2) with symptoms not caused/contributed to by non-work injury or accident, and 3) had symptoms start after beginning the current job. The relationship between cases and work demand, job stress, ergonomic factors, and workstyle measures was evaluated.

Upper extremity symptoms were strongly associated with work demands, ergonomic factors, and workstyle measures but not job stress. The authors felt this may be due to the definitional differentiation between job stress (presence of conflicts with supervisor/coworkers, work urgency) and workstyle measures (employee belief/behavioral response to work conditions).

The authors propose that upper extremity symptoms may be best predicted by a biobehavioral workstyle model comprised of work demands (high workload and work load variability), physical risk factors (awkward posture, repetition, force) and workstyle (employee response to work).

Article Title: Workstyle and Upper-Extremity Symptoms: A Biobehavioral Perspective

Publication: Journal of Occupational and Environmental Medicine 47: 352-361, 2005

Authors: R A Nicholas

Research Summary #2:

Pressure Can Overwhelm Nerves

Key Point: Human and animal studies are supplying the pieces to complete the picture of nerve pathogenesis which will facilitate the understanding/treatment/accommodation of peripheral nerve conditions like carpal tunnel syndrome.

Insight into the role of tissue pressure and vibration in nerve injury pathogenesis, such as carpal tunnel syndrome, is offered through a literature review of animal and human studies by Keir and Rempel.

Twenty mm Hg of pressure on a nerve can interfere with internal blood flow. Thirty mm Hg of pressure can alter axonal transport and cause both nerve swelling and nerve dysfunction. Brief duration/low magnitude pressure can induce nerve injury which triggers a repair process that can take months to complete.

As finger, wrist, and forearm posture deviates from a neutral position, pressure within the carpal tunnel increases in a dose-response relationship. Fingertip loads (both pulp and pinch grip) increase carpal tunnel pressure in a dose-response manner with the critical pressure of 30 mm Hg created by 36.2 pounds of pinch grip force.

Hand tool vibration levels applied to a rat hindlimb for four/five hours a day for five days produced nerve tissue changes similar to pressure (intraneural edema and altered myelinated/unmyelinated fiber structure). Human nerve tissue degeneration of the same nature was seen among workers who used vibrating tools.

Studies are beginning to assess the relationship of finger/wrist posture on wrist contact/hydrostatic pressure and carpal tunnel area/volume/shape.

Article Title: Pathomechanics of Peripheral Nerve Loading: Evidence in Carpal Tunnel Syndrome

Publication: Journal of Hand Therapy 18: 259-269, 2005

Authors: P J Keir and D M Rempel

This article originally appeared in The Ergonomics Report™ on 2006-02-08.