You may be like me. I don’t really vary by much more than 5s/100 over a season going from untrained to race ready. What is your swimming background like? I came up through the county ranks in the UK - state level USA. I swim about 1:20 flat out for a 100, a decent set hitting about 1:27-1:30 on repeats in the off season, and drop to about 1:15 flat out and around 1:23-25 repping through a set the week before an Ironman. For me, I cannot increase my arm tempo. I am a strong and slow stroker. If you are over gliding, then you should work on your tempo, but that is easier said than done. I find that if I increase my arm speed, I fatigue quickly, and my stroke gets out of whack as the session goes on.
What are your target races? You are swimming around my pace by the sounds of things, so 53-55 min Ironman swim time? I have come to accept that this is really good enough for me - front of age group pack, off the back of the pros, but then I am not going to ever race pro. If you are doing races such as ITU at a high level where speed is of the essence, then you need to look at form, strength and tempo. If you increase your ability in these three, you will go quicker.
Are you doing weights?
Is your stroke as refined as it can be, or are you an ‘Arnie’ in the water?
Is your stroke tempo too slow?
Now, it isn’t a case of just increasing your tempo and you will go faster. Like me, your stroke might go to hell and you will be slower.
If you are a somewhat lazy swimmer as I am, then I would recommend two things:
I have joined a masters squad this year - not because I need to increase my swim time as it is, but because it is more fun. I am however seeing some good results, and I am probably at my summer speed now in February, so it is a little bit of a voyage into the unknown with regards to what speed I can get to for July. The other thing this has done is push me. As I say, I am lazy in the water. The squad I am with were national champions last year and I just about hang on the back of lane 1.
Secondly, if you need to increase speed, how about doing very short reps? A set like 20 x 25m with plenty of rest at each end - repping on a minute say? This will increase your tempo over time, and potentially your power as a result. It will take time, but you will hopefully get used to swimming a slightly higher tempo which will translate into your longer swims.
It is easy I think for us triathletes to be quite lazy with our swims. We focus on long sessions and don’t truly push ourselves. Get in, knock out 20 x 100’s or something similar holding a steady tempo, but don’t truly get out of sorts. I have left some sessions with my masters squad unable to pull myself out of the pool or open doors for the next few hours. Eye opening.