Speed and whole body vibration in a sample of grapple skidders from the US South
Whole body vibration (WBV) is a risk factor for the development of musculoskeletal disorders among logging equipment operators. In 2014 we sampled operator exposure to WBV in logging equipment common in the southern United States. The average weighted acceleration anticipated over an eight-hour day (A(8)) was 0.64 ms-2 (sd 0.32) for trailer mounted loaders, 1.04 ms-2 (sd 0.42) for wheeled feller-bunchers, and 1.58 ms-2 (sd 0.34) for skidders. All were above the European Union (EU) action value of 0.51 ms-2, but skidders were consistently above the limit value of 1.15 ms-2. Because travel speed is important for skidder productivity, we explored the relationship between WBV and speed. We accumulated data over 52 second intervals (0.0006 day) generating more than 2900 intervals from 11 sites. A regression analysis by site revealed significant positive relationships between speed and vibration for 9 of 11 skidders (R2 from 0.02 to 0.62). Speed distributions revealed three operational styles and mean speeds ranging from 1.15 to 1.54 ms-1. A stepwise regression with speed, and speed2 for all skidders was significant (F 125.51, MSE 39.77, R2 0.34 and df 12, 2898) and included speed, speed2, operational style, locations (trail or landing), and all but one of the two-way interactions. When A(8) was estimated for other skidders, the model generated important differences in A(8) for speed and operational styles. Operational planning and training about tradeoffs between speed and productivity could be an important administrative control for reducing exposure to WBV.