Exercises to activate and strengthen the lower traps and serratus anterior
So having discussed the role of both the lower fibres of trapezius and the serratus anterior in upwardly rotating the scapula to allow movement of the arms overhead, I now plan to show a few exercises which should help get these muscles working as they should. The name of the game with these is 'feeling' the exercise; what I mean by this is concentrating your mind on which muscles are effecting the movement; ensuring form is perfect; to this end it is not necessary and indeed counter-productive to load on weight. Besides the fact that no-one cares how much weight you use for esoteric rehab exercises, it will also serve to force your body to compensate and revert to stronger muscles, missing the point of the exercise altogether.
The first exercise is the Prone Y, a component of the popular YTWL complex. The Y portion of the complex in particular is designed to teach activation of the lower fibres of trapezius. To perform this exercise, the torso needs to be approximately parallel to the floor. You can either lean over, keeping your spine extended, or lie on a bench. Let your arms hang down in front of you. To initiate the movement, squeeze the scapulae back and down (retract and depress). Now, lift your arms out to the side, maintaining an angle of about 135 degrees to your body. Your thumbs should be pointing towards the ceiling. Once your arms have been lifted as far as possible, try to make them as long as possible. You should not be shrugging your shoulders to your ears - there should be a feeling on intense contraction between the scapulae. Lower the arms and repeat.
The next exercise is the Scap Pressup. This starts off similarly to a normal pressup. Assume a strong planked position. Now, lower your body by retracting and depressing your scapulae, keeping your elbows locked out. Only your scapulae should move; this is quite hard to do at first but will come with practice. Once you have lowered as far as possible, reverse the movement by protracting your scapulae as hard as possible and driving upwards. The range-of-motion is quite small so don't be tempted to extend it by either bending at the elbows or sagging at the waist. Keep it tight and activate the serratus.
This next exercise is also one for the Serratus Anterior. I have to credit James Jowsey with showing this to me. I'm not sure if it has a name. Stand about 18 inches or so from a wall. Lean forward and place both forearms in contact with the wall, having your elbows flexed to about 90 degrees. To start the movement, slide one arm upwards, keeping the hand and forearm in contact with the wall at all times. Drive the shoulder forward during this movement to further activate the serratus. If done correctly you should feel intense contraction under the armpit on the side of the chest wall. To aid in feeling this, take the non-working hand off the wall and place it just down from the armpit on the side of the chest. You should feel the muscular slips of the serratus bulge out as you perform the motion.
Finally, I've included the Scap Wall-slide. This exercise generally improves scapular retraction and humeral external rotation, as well as actively stretching the pecs and lats and improving mobility of the thoracic spine. We'll get on to why these are such good things later; suffice to say that you get a lot of bang for your buck and should therefore do it. It is a hard exercise; as you can see in the video, I am only capable of a fairly limited range-of-motion. Even this causes intense contraction of the muscles retracting the scapulae and extending the thoracic spine. To perform the movement, sit against a wall. Keep the full length of your spine in contact with the wall at all times. Retract your scapulae and put your arms in contact with the wall, elbows flexed at 90 degrees, so you form an L shape with each arm. Now, keeping all the arm in contact with the wall, slowly slide your arms up the wall. The forearms should remain at 90 degrees to the floor at all times. Move only as far as flexibility allows, then slide the arms back down. This is tough, but persist and shoulder mobility will improve dramatically.
These four exercises would be an excellent part of a warm-up before a workout that makes extensive use of the shoulders. If you're training right, this will be every workout. They are worth doing on rest days also, particularly if you get shoulder pain.