I used to go swimming often and manage between 30-40 lengths in half an hour. But I was one of those people who came out the pool with dry hair as I always kept my head above the water. I had a feeling I wasn't doing it right (breaststroke) as it strained my neck a bit but I'd never been shown how to do it properly. Anyway a colleague told me that if I swam under the water & brought my body up to take a breath, this 'proper' technique is much more effective. So I nicked my DD's goggles & tried the 'proper' technique today. OMG what a difference! I found it really hard to get my breathing technique at first but got used to it. But I only managed a max of 20 lengths, having to take a break after each 2!! And I'm still completely knackered an hour later! Guess this technique works!