Rectus abdominus

The most obvious of your abdominal muscles if you're built like a male model*. Abdominals are important in archery as they help stabilise the torso and keep the body upright. See also the section on the oblique, another important abdominal muscle

* If you're built like a male model this is your 'six-pack'. In many male archers, unfortunately, it's covered by the evidence of the six-packs of the previous ten years...