Impacts of Different Sitting Positions on Lumbar Multifidus Muscle Thickness and Hardness: A Crossover Comparative Study

Abstract

[Purpose] To clarify the impacts of different sitting positions on lumbar multifidus muscle thickness and hardness. [Participants and Methods] The participants were 14 healthy adult males. Their lumbar multifidus muscle thickness and hardness were measured under 2 conditions: 1) adopting a study posture in a normal sitting position; and 2) maintaining a study posture in a normal sitting position for 5 minutes and returning to the normal position. There were 6 study postures: 1) good posture, 2) slouched posture, 3) on a balance disc, 4) on a balance ball, 5) crossing the right leg, and 6) crossing the left leg. Four measurements were performed in the 6 postures. Measurement values before and after each condition were compared, and the change rates among the postures were examined using a multiple comparison test. [Results] There were significant decreases in muscle thickness after adopting Postures 2, 5, and 6 under Condition 1 and Posture 1 under Condition 2. Multiple comparisons on the change rates among the postures revealed a significant increase in muscle thickness when adopting Posture 4 compared with 2 under Condition 1, and significantly lower muscle hardness when adopting Posture 6 compared with 2 under Condition 2. [Conclusion] Lumbar multifidus muscle thickness and hardness decreased after sitting while adopting a slouched posture.