Underhand grip is going to be more lats because the lats have the most leverage when your arms are adducted to the body. The lats use the ribcage as a fulcrum. Once the arm moves away from the body- the lats can no longer use the ribcage as fulcrum and its no longer the lats doing the work). If you going from pronation (overhand) to supination (underhand) you’ll automatically notice as you do so, your arm begins to move away from your body. This will engage more of the upper back and less lats. I feel like I may to get a question on this, but even though I am pulling past my body slightly in the underhand pulldowns, doesn’t mean there is absolutely no lat musculature involved. With an underhand grip, you will get more lats than upper back. With an overhand grip, you will get more up