To better target the rear shoulder (posterior deltoid) during a pulling exercise, Enzo Foukra advises avoiding excessive squeezing of the shoulder blades and slightly rounding the back.

noli's read

This advice offers an interesting technical nuance aimed at further isolating the posterior deltoid by limiting the involvement of shoulder blade retractor muscles, such as the middle trapezius and rhomboids. In biomechanics, strong scapular retraction places these muscles in a shortened position that favors their recruitment, which can effectively 'steal' a portion of the tension initially intended for the posterior deltoid during rowing or reverse fly-type movements. While sports literature often emphasizes the importance of a stable posture (neutral scapulae) for joint health (NASM, NSCA), the idea of slight protraction (rounding the upper back) to isolate the posterior deltoids is a practice observed in bodybuilding to optimize specific work on this area. This is not a universal safety rule—on the contrary, a rounded back is generally discouraged to protect the spine under heavy loads—but in a context of pure isolation with moderate loads, it can help direct tension to the desired target. The potential for exaggeration lies in the risk of technical confusion: for a beginner, 'rounding the back' can be misinterpreted and lead to unnecessary strain on the lumbar or thoracic region.

the sources

No named source held this one up — that absence is part of the verdict.