When working with either young, or older swimmers, reaching full extension in breaststroke is sometimes a challenge. Why do it: While you wouldn't do this in a race, locking the thumbs in extension starts to teach what true extension is. How to do it: 1) Slow down the stroke, and focus on really reaching forward. 2) During extension, wrap your thumbs together and glide. 3) Squeeze in on the head like a modified streamline. How to do it really well (the fine points): Slow down more. The goal of this drill is to maximize the stretch on each stroke, and you want to wait between each stroke until you really feel it. By locking the thumbs, some swimmers will be able to squeeze every last bit of integrity from the bodyline and extension of the arms. Switch back to regular swimming, trying to maintain the feeling of extension, stretch, and body position that you achieved with the thumb-lock.