Take Home Points on Bridging:
  1. The bridge with hip adduction increases core and glute activation.

The bridge may seem like an out-dated Jane Fonda exercise move, but this simple exercise can likely improve glute activation.  What is glute activation?  You activate your glutes when you try to squeeze your two butt cheeks together.  When was the last time you seriously tried to squeeze your butt together?  No one deny the important of the glutes for ground-based sports and protection of the knees and low back, making the bridge a staple for many preventative and rehabilitation programs.

Many simply perform the bridge while lying on their back, but perhaps there are other ways to increase core and glute activation with the bridge…
Bridging with Hip Adduction Increases Core Activation
Jang (2013) had fourteen healthy adult females (~29.5 years) without low back pain performed bridging exercises with and without hip adduction. The EMG activities of the rectus abdominis (RA), external oblique (EO), internal oblique (IO), and gluteus maximum (GM) muscles were recorded. 

This study used surface EMG, one drawback of the study.
The EMG activities of all muscles were significantly increased during the bridge with hip adduction, compared to the traditional bridge.

Why More Core and Glute Activation?

This increased muscle activation may be from the hip adductors origin (proximal to the inferior aspect of the body and ischium), making a control alter pelvis stability.

Now, studies assessing single leg bridges are necessary to see if hip adduction or single leg bridges result in greater glute activation. However, it is key to remember, finding the most appropriate exercise intensity is more important than simply finding the hardest exercise!

Reference:
  1. Jang EM, Kim MH, Oh JS. Effects of a Bridging Exercise with Hip Adduction on the EMG Activities of the Abdominal and Hip Extensor Muscles in Females. J Phys Ther Sci. 2013 Sep;25(9):1147-9. doi: 10.1589/jpts.25.1147. Epub 2013 Oct 20.