The effects of work experience, lift frequency and exposure duration on low back muscle oxygenation.

BACKGROUND Previous studies have shown changes in low back muscle oxygenation after static muscle contractions or short-term dynamic lifting exertions. The aim of this study was to document the changes in low back muscle oxygenation during prolonged lifting activity over an entire workday as of function of work experience and lift frequency. METHODS Four novice and six experienced subjects participated in a lifting study in which they lifted load with a given weight at one of five different frequencies (2, 4, 8, 10, 12 lifts/min) for an 8-h period. Oxygen saturation of the left and right erector spinae was measured continuously and non-invasively using near-infrared spectroscopy during each lifting session. FINDINGS Exposure duration had a statistically significant effect on muscle oxygenation level (P<0.0001). Oxygen saturation in the erector spinae increased during the 8-h lifting period. As lift frequency increased, back muscle oxygenation in experienced subjects also increased. In general, the increase in muscle oxygenation for experienced subjects was less than that for novice subjects. INTERPRETATION This study suggested that the requirement of oxygen for the low back muscle in a typical industrial lifting job increased over time and experienced workers responded differently from the novice subjects. These findings may provide more insight into the physiological changes of the working muscle and the potential risks of developing muscle injury.