PrimarySecondaryNot worked
This movement mainly trains triceps, and also recruits Rear delts.
With the arm overhead, the long head of the triceps is stretched — it is the only one of the three that crosses the shoulder, and this is the only position that loads it truly lengthened.
Ten to fifteen reps, moderate load. Full range matters more than weight here: the stretch is what justifies the movement.
Letting the elbows flare out on the way up. Load spreads onto the shoulder, and the long head loses exactly the stretch this position was chosen for.
The variants REPWIND's catalogue carries, under the name the app shows:
The journal, the anatomical map and all 257 catalogue exercises — free to start.