The effects of ratio in the multifidus muscle thickness according to various angle of mediolateral ramp during double stance

[Purpose] This study was conducted to predict the risks of standing on mediolateral ramps by identifying the ratios of the multifidus muscles on the two sides of the spine when standing postures are maintained on mediolateral ramps of diverse angles. [Subjects and Methods] The study was conducted with 15 healthy adult males. All subjects participated voluntarily. Mediolateral ramps at five angles (0°, 5°, 10°, 15°, and 20°) were used. Ultrasonography was used to determine the thicknesses of the multifidus muscles under individual conditions. [Results] The ratio of the left/right multifidus muscles showed statistically significant differences as the angle of the mediolateral ramp increased. Post-hoc test results showed that the use of the two multifidus muscles was asymmetric on mediolateral ramps at angles equal to or larger than 10°. [Conclusion] The asymmetric use of the multifidus muscles began on a mediolateral ramp at an angle of 10°, suggesting that subjects with instability in body control might have risk factors such as falls on mediolateral ramps with angles equal to or larger than 10°. Therefore, caregivers must be attentive and/or assist patients and older adults when they are walking on ramps at angles of approximately 10° and up in their daily lives.