The combined fatigue effects of sequential exposure to seated whole body vibration and physical, mental, or concurrent work demands

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.

Fig 1. Experimental conditions and seated whole body vibration exposure.

Fig 2. Experimental protocol.

Top Inset: Experimental study collection protocol. Conditions presented in 2, 15-minute bouts, WBV in a single 30-minute bout. Bottom Inset: (A) Pre- and Post- session baseline test battery, (B) Intermediary test batteries between first bout of condition and ATV simulation and between ATV simulation and second bout of condition.

Fig 3. Visualization of trends of measures demonstrating statistically significant time effects.

Values standardized to z-values to visualize trends of measures for each condition. Data plotted over time at intervals of time at which a test battery was collected (cutaneous sensation and Purdue pegboard test limited to Pre-and Post). Increase z-value score indicate increasing fatigue based on conventional interpretation of each measure. Decrease z-value score indicate decreasing fatigue. (A) Control Condition. (B) Physical Condition. (C) Mental Condition. (D) Concurrent Condition. Statistical post-hoc comparisons between time periods were shown in Table 3.