For me (and probably many) it's volume. May seem obvious, but so many triathletes aren't great swimmers and try the less is more approach - doesn't translate to good results unless you have a swim background.

Here's my recent example: From October to February I swam once a week - sometimes none if it didn't work with the family (2nd child was born in September). Over that time frame my time for faster 100's dropped by 6-7 seconds. Starting in March I added in a weekend swim before my long run on Sunday morning. By mid April I had gained back around 3 seconds by doing 2x swims a week. During our school spring break last week we traveled, and our time share had a 20m pool that I swam in every morning. After getting in nearly 16k yards in the week, yesterday I was only 1-2 seconds off my faster 100 time from last summer. Upping the yards and having a higher volume week kicked things into gear. Just my personal experience, and I'm sure getting in a third swim would probably get me back to the times I was seeing last season.

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