For lateral raises, do not lift your arms above the shoulder line (parallel to the floor) in order to avoid over-engaging the upper trapezius and to maximize work on the lateral deltoids.

noli's read

This advice is based on the biomechanics of the movement: the lateral deltoid is the primary mover of abduction up to approximately 90 degrees. Beyond that, a study published in the 'Journal of Electromyography and Kinesiology' (electromyography) indeed shows increased activation of the upper trapezius to assist in scapular rotation. The creator here aims for specific isolation of the deltoid, which is a classic approach in bodybuilding for aesthetics. However, labeling moving past the shoulder line a 'major mistake' is a simplification: some comprehensive training programs incorporate full ranges of motion for shoulder health. This is not an absolute danger, but a choice of muscle targeting. The analysis is therefore technically consistent with isolation objectives, while remaining a training style preference rather than a universal truth.

the sources

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