Relationships between lower limb and trunk discomfort and vascular, muscular and kinetic outcomes during stationary standing work.

Standing work is associated with discomfort and symptoms in the trunk and lower limb. However, mechanisms underlying these observations are poorly understood. Moreover, most research on standing-related symptoms has focused on only one region (lower limb or trunk), and has not considered the impact and interactions between vascular, muscular and balance outcomes. We measured foot and soleus blood flow, ankle mean arterial pressure, muscle activity of the plantar and dorsi flexors, gluteus medius and trunk flexors and extensors, center of pressure changes and leg and back discomfort in 18 healthy volunteers performing a repetitive box-folding task for 34 min. Results show significant decreases with time in lower limb muscle activity (p<0.00053), and increases in foot blood flow and center-of-pressure mediolateral sway amplitude (p=0.00066). There were significant time effects on back (p=0.017) and lower limb (p<0.000001) discomfort, the latter significantly correlated (r=0.35) to time-related increases in foot blood volume. No changes were correlated to the increase in back discomfort. Results suggest that the origin of standing-related lower limb discomfort is likely vascular in origin, whereas back discomfort is likely multifactorial, involving muscular, vascular and postural control variables.