Shoulders shrug during the pause
Upper traps elevate to maintain the position; medial delt is bypassed.
Overactive muscles
Upper trapeziusLevator scapulae
Corrective work
Foam RollUpper traps↗StretchLevator scapulae stretch↗Upper traps elevate to maintain the position; medial delt is bypassed.
Arm angle changes; the medial delt loses its optimal position.