Investigation of trunk muscle activity for modified plank exercise: A preliminary study

Abstract

BACKGROUND: Plank exercise is one of the most popular methods of exercise for strengthening the trunk muscles. However, many individuals might have some difficulty performing this exercise. OBJECTIVE: This study aimed to identify trunk muscle activation with postural changes and the use of dynamic cushion during a traditional plank exercise in order to propose a set of exercise levels according to exercise performance ability. METHODS: Seven participants were asked to perform the traditional plank exercise (TPE), a modified plank exercise (MPE), an unstable traditional plank exercise (UTPE), and an unstable modified plank exercise (UMPE). The UTPE and UMPE use a dynamic cushion to simulate an unstable surface. Surface EMG of the ractus abdominis (RA), external oblique (EO) and erector spinae (ES) was recorded while participants were engaged in these exercises. The plank exercises were performed for ten seconds with a ten-minute break between each posture. RESULTS: Comparing the measurement results from the four postures, significant differences were observed in the RA and EO (p < 0.05) which were found to be significantly different during the UTPE than during the MPE and UMPE (p < 0.05), while TPE showed a significant difference only in the left EO muscle activation (p < 0.05). In terms of the right RA and the left EO, a significant difference was observed only with respect to MPE (p < 0.05). CONCLUSION: The results of this study may be used as a basis to arrange the order of exercise, based on the level of muscle activation appropriate for the participant's exercising ability. Individuals who have difficulty performing the TPE, may first perform the MPE and the UMPE.