Let me guess...
Your "core workout" looks like this: planks for time, Russian twists, flutter kicks, sit-ups, maybe some dead bugs if your coach is feeling fancy.
Here's the problem: You're training your core like a weekend warrior, not an elite swimmer.
While you're wasting time with exercises that were outdated 20 years ago, fast swimmers are using a completely different approach that builds ACTUAL swimming strength and mobility.
The truth? Your current core training is making you SLOWER.
Those endless crunches and planks just lock down your core and don't train it for flexible and explosive movements you need in the pool...