Which trunk exercise most effectively activates abdominal muscles? A comparative study of plank and isometric bilateral leg raise exercises

BACKGROUND Various forms of trunk exercise have been used for increasing abdominal strength. The plank exercise and bilateral leg raise exercise are one of these trunk exercises. However, there are few studies that compared the effects of these exercise variations. OBJECTIVE The present study aimed to investigate how effectively the trunk muscles during plank and bilateral leg raise exercises are activated. METHOD Surface electromyography responses of the rectus abdominis, internal oblique, and erector spinae muscles were investigated during the plank and bilateral leg raise exercise with different hip position. A total of 18 healthy, physically active female volunteers completed the normal plank exercise, plank exercise with placing the lower leg in a horizontal condition, bilateral leg raise exercise, and bilateral leg raise with lower leg as horizontal condition. RESULTS The horizontal condition caused significant increases in activity of the internal oblique muscles compared with the general condition (p< 0.05). The bilateral leg raise exercise showed significantly greater activation in the rectus abdominis compared to the plank exercise (p< 0.05). CONCLUSION The present study showed that the horizontal condition had the advantage of activating the internal oblique muscles, and the leg raise exercise is effective in strengthening global muscle such as the rectus abdominis.