Effects of cognitive loading on lumbar flexion relaxation phenomenon in healthy people.

[Purpose] The objective of this research was to examine the impact of cognitive load on the flexion relaxation phenomenon (FRP) during trunk flexion and return from flexion task. [Subjects and Methods] Twenty-two healthy subjects (18 males, 4 females) participated in the study. Each participant was exposed to 3 experimental conditions: no cognitive task, easy cognitive task and difficult cognitive task. Surface electromyography was used to measure lumbar erector spinae muscles activity level. Flexion relaxation ratio (FRR) was compared in order to assess the differences between the three experimental conditions during flexion and extension (FLX FRR and EXT FRR). [Results] The FRR was decreased with increase in cognitive difficulty; the difficult cognitive task was associated with significant lower value of FLX FRR in both sides. However, these changes were not significant in easy cognitive task. In addition, the EXT FRR was decreased in cognitive task conditions, but these results were not statistically significant except for difficult cognitive task condition in comparison to no cognitive task condition in left side. [Conclusion] These findings suggest that cognitive loading can affect FRP in healthy subjects.