INTRODUCTION: Sit-to-stand (STS) test is used for assessment of lower limbs function at different seat heights. It was reported that electromyographic (EMG) activity during STS movement changed by seat height or initial position of lower limbs and trunk. (Kim and Ju, 2019, Goulart and Valls-Sole, 1999) However, the change in activity pattern of the trunk muscles, especially deep muscles such as tranversus abdominis (TrA) and psoas major (PM), during STS movement at different seat heights is unknown. Then, the purpose of this study was to investigate muscles activity using intramuscular EMG during STS movement and compare between different seat heights.
METHODS: Fifteen healthy men participated in this study. EMG and motion analysis data were obtained synchronously during STS movement for 3 sec. The participants performed the STS movement with bilateral and single (right) leg from following different seat heights; 10 cm, 20 cm, 30 cm, 40 cm. Fine-wire electrodes were inserted into the right TrA, PM, and gluteus minimus (Gmin) under ultrasound guidance. Surface electrodes were attached to the rectus abdominis, external oblique (EO), internal oblique (IO), erector spinae (ES), multifidus (MF), gluteus maximus, rectus femoris (RF), biceps femoris (BF) on the right side. The STS movement was divided into flexion and extension phases by using the hip flexion angle. For each muscle, normalized EMG amplitudes (%MVIC) in each phase were calculated and evaluated by using the 2-way analysis of variance (phase and seat height). Significant levels were set to 0.05.
RESULTS: The EO activity showed significant interaction during STS movement with bilateral and single leg. The EO activity during flexion phase at 10 cm height with bilateral and single leg were respectively 11.6 ± 7.5% MVIC and 46.4 ± 7.5% MVIC, and significantly greater than those of other tasks. The Gmed activity showed significant main effect of seat heights during STS movement with single leg, and gradually increased as the seat height is lower. There were no significant differences between the seat heights in the deep muscles such as the TrA, PM, and Gmin.
DISCUSSION: Previous study (Eom et al, 2016) reported that the the abdominal muscles activity increased with hip and knee flexion angle at initial position during STS movement since the function of trunk and hip flexion required to move the center of mass toward anterior direction. Therefore, the EO which has greater torque of trunk flexion showed higher activity during STS movement from low seat height. Additionally, the Gmed activity gradually increased with lower seat heights during STS movement with single leg. It is considered that the Gmed required to control the greater torque of hip abduction/adduction on frontal plane at lower seat heights. In contrast, the deep muscles did not show significant differences. The results suggested that specific exercise with low load is necessary to enhance the activity of the deep muscles.