A case study of assessing psoas major muscle activity in dolphin kick swimming using muscle functional MRI

The purpose of the present study was to examine the validity of muscle activity assessment using muscle functional MRI (mfMRI) and to evaluate the muscle activity level of the psoas major muscle in dolphin kick swimming using mfMRI as a case study. One male collegiate swimmer participated in this study. The participant performed two dolphin kick swimming trials with the different methods of muscle activity assessment: 1) MRI imaging before and after dolphin kick swimming and 2) measuring surface electromyography (sEMG) during dolphin kick swimming. The subjective muscles of mfMRI were psoas major, rectus abdominis, low back muscles (erector spinae and multifidus), rectus femoris, and biceps femoris and that of sEMG were rectus abdominis, erector spinae, rectus femoris, and biceps femoris. As the results of mfMRI, the change of T2 value in psoas major muscle was 13.1%, which was the second highest activity level after that of the biceps femoris muscle (14.8%). Furthermore, the cosine similarity of the muscle activity levels in the four muscles (excluding the psoas major) evaluated from both mfMRI and sEMG was 0.99, and therefore, it was suggested that the muscle activity assessment using mfMRI might be sufficiently valid.