Abstract
Many occupations in agriculture, construction, transportation, and forestry are non-routine, involving non-cyclical tasks, both discretionary and non-discretionary work breaks, and a mix of work activities. Workers in these industries are exposed to seated whole body vibration (WBV) and tasks consisting of physical, mental, or a combination of demands. Risk assessment tools for non-routinized jobs have emerged but there remains a need to understand the combined effects of different work demands to improve risk assessment methods and ultimately inform ergonomists and workers on optimum work arrangement and scheduling strategies. The objective of this study was to investigate fatigue-related human responses of WBV sequentially combined with physical, mental, or concurrent physical and mental demands. Sixteen healthy participants performed four conditions on four separate days: (1) physically demanding work, (2) mentally demanding work, (3) concurrent work, and (4) control quiet sitting. For each condition, participants performed two 15-minute bouts of the experimental task, separated by 30-minutes of simulated WBV based on realistic all-terrain vehicle (ATV) riding data. A test battery of fatigue measures consisting of biomechanical, physiological, cognitive, and sensorimotor measurements were collected at four interval periods: pre-session, after the first bout of the experimental task and before WBV, after WBV and before the second bout of the experimental task, and post-session. Nine measures demonstrated statistically significant time effects during the control condition; 11, 7, and 12 measures were significant in the physical, mental, and concurrent conditions, respectively. Overall, the effects of seated WBV in combination with different tasks are not additive but possibly synergistic or antagonistic. There appears to be a beneficial effect of seated ATV operation as a means of increasing task variation; but since excessive WBV may independently pose a health risk in the longer-term, these beneficial results may not be sensible as a long-term solution.
Highlights
Work tasks in manufacturing settings are often predictable; jobs in agriculture, transportation, forestry, and construction are typically less routinized, non-cyclical, peripatetic, and involve both discretionary and non-discretionary work breaks [1,2,3]
Back/lower extremity Maximum Voluntary Contraction (MVC) force significantly decreased as a result of physical activity, but increased after whole body vibration (WBV) (Fig 3B)
Similar to the control condition, heart rate improved after seated WBV and cutaneous sensitivity improved at cessation compared to baseline (Fig 3C)
Summary
Work tasks in manufacturing settings are often predictable; jobs in agriculture, transportation, forestry, and construction are typically less routinized, non-cyclical, peripatetic, and involve both discretionary and non-discretionary work breaks [1,2,3] In these sectors and in many contemporary jobs, workers are exposed to a mix of work activities, including exposure to seated whole body vibration (WBV) with tasks consisting of physical, mental, or a combination of demands [4]. Significant increases in spine loading were observed with concurrent cognitive and physical tasks; less controlled trunk motion and increase in torso muscle co-activation was attributed to work-related mental processing [13] Not surprisingly, both physical and mental demands contribute to decrements in operation system performance, such as increased work error rates [14]
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