Received February 21, 2006
Revised April 6, 2006
Accepted after revision May 25, 2006

¹ Liberty Mutual Research Institute for Safety
² University of Alberta

^* To whom correspondence should be addressed. E-mail: rammohan.maikala{at}libertymutual.com.

	Abstract

Exposure to whole-body vibration is implicated as one of the occupational risk factors for low-back disorders, however its influence on the lumbar muscle physiology is still poorly understood. The objective of this study is to investigate the effects of backrest support and handgrip contractions on lumbar muscle oxygenation and blood volume responses during seated whole-body vibration using a continuous dual wave Near-Infrared Spectroscopy. Thirteen healthy men were exposed to frequencies 3, 4.5, and 6 Hz on a vibration simulator, in randomized order on separate days. Each day the duration of the protocol was 30 min. During the fifth minute of vibration 'with' and 'without' backrest support, participants performed maximal rhythmic handgrip contractions for one minute. In general, compared to without vibration erector spinae oxygenation and blood volume trends decreased with vibration exposure. However, these responses were not influenced by the change in vibration frequency (P>0.05). Sitting 'without' backrest showed a greater decrease in oxygenation (by 27%, P=0.02) and blood volume (by 11%, P=0.05) than 'with' backrest, implying deficiency in oxygen supply due to the sitting posture. Compared to vibration only condition, handgrip work decreased both oxygenation (by 22%, P=0.003) and blood volume responses (by 13%, P=0.04), suggesting postural load due to prolonged sitting combined with physical activity during vibration, might further burden paraspinal muscles. Influence of adipose tissue thickness of the lumbar muscle on optically-derived oxygenation and blood volume changes was inconclusive.

Key Words: Isometric exercise, Muscle, Spectroscopy