[Purpose] The purpose of this study was to investigate the changes in the muscle activities of the neck, trunk, and lower extremities when an unstable base of support and a stable base of support were used in bridging exercises. [Subjects] The subjects of this study were 14 persons in their twenties (9 Males, 5 Females, 23.3 years old, 168.7 cm, and 70.0 kg). [Methods] The subjects performed an ordinary bridging position (stable base) and a bridging position with a dynamic ball cushion (unstable base). The muscular activities of the longissimus capitis and sternocleidomastoid in the neck, the erector spinae and rectus abdominis in the trunk, the rectus femoris and lateral hamstring in the thigh, and the tibialis anterior and lateral head of the gastrocnemius in the lower leg were measured using surface electromyography. [Results] The erector spinae, lateral hamstring and gastrocnemius activities were significantly higher on the unstable base of support than on the stable one. [Conclusion] Activity of muscle groups varies according to the stability of the base of support during bridging exercises. Therefore, conducting bridging exercises with lumbar pain patients requires a gradual change from a stable to an unstable base of support.