This is from the IFBB judging criteria which explains why contests are won from the back
Back Double Biceps (see Figure 4)
Standing with his back to the judges, the competitor will
bend the arms and wrists as in the Front Double Biceps
pose, and will place one foot back, resting on the toes.
He will then contract the arm muscles as well as the
muscles of the shoulders, upper and lower back, thigh
and calf muscles.
The judge will first survey the arm muscles and then do
the head-to-foot survey, during which there are more
muscle groups to look at than in all of the other poses.
This includes the neck, deltoids, biceps, triceps, forearm,
trapezius, teres, infraspinatus, erector spinae, external
obliques, latissimus dorsi, gluteus, thigh biceps, and
calves. This pose, probably more than the others, will
help the judge to determine the quality of the
competitor’s muscle density, definition, and overall
balance.
