| Approximately 4 to 7 percent of workers are exposed to potentially harmful levels of WBV in Canada, the United States, and some European countries (Bovenzi, 1996a). Exposure to vibration is known to cause certain physiological responses. However, there is still a lack of understanding on how these responses tax the neuromuscular system. The objective of this work has been to develop a better understanding on what are the effects of vibration induced fatigue on true proprioceptive and neuromuscular performance. A series of neuromuscular and kinaesthetic tests were performed before and immediately after exposure of 45 min of the experimental protocol chosen for each trial (Standing, Standing with vibration, Squatting and Squatting with vibration)(3.5 Hz) in 12 healthy subjects. A significant decrease in mean maximum voluntary contraction (MVC) torque was produced during extension and flexion POST Squatting Trial (SQT) and Vibration Squat Trial (VSQT) experimental conditions. A significant decrease was also produced POST VSQT in raw electromyography root-mean square (EMG RMS) for the rectus femoris, in twitch PT, Doublet PT and Doublet HRT. Similarly a significant decrease in twitch contraction-time (CT), twitch half-relaxation time (HRT) twitch peak torque (PT) was produced POST SQT. Velocity matching tasks were performed at the knee using three different velocities (30°/s, 90°/s and 120°/s) to assess kinaesthetic sense, before and immediately after experimental protocols. For velocity matching errors, the between-subject factors that were chosen to be evaluated are as follows: Condition (1 Squat, 2 Standing, 3 Squatting with vibration, 4 Vibration), Direction (flexion/extension), Speed (30°/s, 90°/s, and 120°/s) and Time (PRE, POST). However there was a significant difference between directions (F=6.66, P=.027). The results also yielded significant interactions between Speed * Direction (F=5.515, P =.025), Condition * Speed * Direction (F=10.266 Sig=.006), and Condition * Speed * Time (F=4.682, P=.041). It seems that sense of effort and velocities of movement also have a definitive influence on movement matching performance. |
