The back consists of 4 main muscles, the most prevalent being the Latissimus Dorsi (Lats) which contribute to back width and is used for Shoulder Adduction and Extension, the Trapezius (Traps) contributes to back thickness, these are used for Scapular elevation (eg. shrugging) and scapular retraction (eg. a row), similar to the Rhomboid Major and Minor. The Erector Spinae (Spinal Erectors) extend all the way up the back and are used to extend the entire vertebral column (spine).
A study (https://www.ncbi.nlm.nih.gov/pubmed/19826307) has shown that simply thinking about contracting the Lats whilst completing an action involving shoulder hinging increases activation and EMG activity (a recording on electrical activity produced by muscles, therefore indicating usage).
The various sections of the back suggest that skeletal muscles in the back can be split into 2 main sections, the ones moving in a vertical plane and those moving in a horizontal plane.
Vertical plane; pull-ups and pulldowns are considered the main movements within the vertical plane, a study (https://www.ncbi.nlm.nih.gov/pubmed/24245055) has shown that relative Lat activation is fairly even for both movements, however bicep activation is increased during a pull-up, therefore better for indirectly targeting the biceps, however when aiming to singularly isolate the Lats, the pulldown movement is more effective. Furthermore, the usage of a pronated grip (overhanded) is shown to be more effective than using a supinated grip (underhanded). (https://www.ncbi.nlm.nih.gov/pubmed/20543740)
Horizontal plane; variations of the rowing movement are used to target the rhomboids and traps as rows involve scapular retraction and extension. Studies have indirectly indicated that movements not involving the need for stability increase EMG activity within the muscles, therefore a movement such as a bent over row will be less effective than a chest supported row.
The Lats and Traps are type 2 dominant, therefore are fast twitch muscles meaning they respond better to higher loads (higher weights) for lower reps, therefore a decrease in volume with an increase in overall load will be more effective for targeting these muscles.
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