The bird dog movement pattern is a firm favourite with physios, however its transference is relatively low across tasks performed at high force. The Bird Dog arms is a good exercise to start the pattern of loading across the the lower back, across into the thoracic region of the opposite side and into the lifting shoulder. As well as this, the hand that is in contact with the floor is getting a lot of feedback and is therefore being worked at the same time, despite it feeling like it isn't doing anything
Hands under eyes for more serratus anterior
Balance an imaginary drink between shoulder blades
Zip up your abdominals
Targeted muscles trained
Key movements trained
Scapular upward rotation
Rotator cuff co-contraction (weight bearing arm)
Shoulder proprioception (weight bearing arm)
Due to the change in the body's position relative to gravity pull on your body, this may unlock overhead positions when they are unavailable when standing. This can be a very useful way to bypass the muscles of the front and side of the shoulder and work the back of the shoulder, which is has a big influence over shoulder health.
This can be considered a low load shoulder stability or proprioception exercise. The hand in contact with the floor passes force up through the arm and into the shoulder joint, this force is adapted for by the rotator cuff muscles to create stability in the shoulder joint. Intent is important, so pushing that hand into the floor actively can be useful for increasing the demand of the exercise.
The asymmetrical nature of the exercise, will create a diagonal force from the opposite hip to the lifting arm. This mechanism can be affected during shoulder pain, so this exercise may work well to begin addressing the dysfunction or keeping it at bay if pain is in your recent past.