Effect of flooring on lower extremity discomfort and fatigue during long-term standing/walking: evaluation of muscle oxygenation as an objective measure of fatigue using near infrared spectroscopy

Long-term standing is associated with multiple health problems affecting the lower extremity including musculoskeletal discomfort and fatigue. Unfortunately, many occupations require workers to endure prolonged periods of time spent standing. This research study investigated the effect of anti-fatigue flooring on subjective measures of discomfort and behavioral responses during long-term standing and walking. In addition to other measures of fatigue, near infrared spectroscopy was used to measure tissue oxygenation in the soleus and erector spinae muscles. Changes in muscle SO2 can provide insight to the physiological processes that occur within muscles throughout long-term standing and walking. The goal was to determine the association between muscle SO2 and subjective discomfort measures. Three flooring surfaces were examined in this study: a hard tile, a standard ergonomic soft mat, and a rubber tile. Subjects stood for 6 hours and walked for 2 hours on each of the 3 flooring surfaces. During this time, subjects rated levels of perceived discomfort while objective measures of fatigue were monitored. Flooring surface had a minimal impact on subjective discomfort during long-term standing. Additionally, erector spinae and soleus SO2 were poorly related to subjective discomfort ratings. No significant changes in muscle SO2 were found over time standing however, a positive relationship was revealed between soleus SO2 and postural movements. Flooring effects were found after just 1 hour in subjective measures during long-term walking. Walking on the soft mat reduced overall leg tiredness, upper back discomfort, ankle discomfort, and feet discomfort compared to walking on the hard tile. Muscle SO2 significantly increased from resting values but similar to the standing protocol, no flooring effects were found during long-term walking. The results from this research suggest the development of subjective discomfort during long-term standing is not easily related to changes in muscle SO2 likely due to the increase in postural movements. The effect of flooring on muscle SO2 is inconclusive due to the similarities in subjective discomfort found across flooring conditions examined in this study