Repeated muscle contractions with brief holds are more effective for building neuromuscular pathways than static holds.

“one of the advantages however of doing these brief 10-second holds and really focusing on the contraction of the abdominals hard or as hard as you can and then releasing is that as opposed to doing a long hold just trying to hold as long as you can and building a lot of endurance in the abdominals when you repeatedly contract a neuromuscular connection you build the pathways you basically allow the pathways that can engage those strong muscular contractions to a greater degree than if you're trying to just statically hold that particular position for a very very long time like 30 seconds or 60 seconds or longer”