Dr Mike Israetel:
"In reality, the biceps are so poorly leveraged to be exposed mechanical damage, produce so little force…
The forearm flexors of most individuals are a roughly even mix of fiber types, so on paper you should be aiming to train biceps with a wide mix of rep ranges.
However, your biceps get pretty much all the heavy work they need as contributors to your heavy back work, and the bicep isolation work you do for them should likely be biased towards higher reps.
Additionally, curling for super heavy (sets of 6 or less) sets can be unsafe, so it’s best to focus most of your bicep volume between 8 and 15 rep sets, with occasional uses of higher rep ranges for metabolite work."