This provides an excellent opportunity to explain the contrast between your run/bike training and the sets you do at coached swims. I’ll note first that I’ve completed open-water swim events of 40km-plus in length, training mostly off pool repeats of 200m or less, saving longer swims for open water – so obviously it’s very different to training on land.
If we take ‘steady aerobic swim’ to mean a continuous swim of 20-40mins in length, this would make sense if swimming was more like cycling and running. However, the factors determining how well you swim, and how the swim affects your ability to perform your best across all three disciplines, are very different. A quick summary:
To have your best race, your aim is to swim your desired pace as easily as possible, saving energy to work harder, and for longer, on the bike and run. You convert effort into speed far more efficiently on land than in the water, thus bike and run workouts should be more aerobically demanding.
How fast you run and bike is determined 70% or more by aerobic capacity. Whereas for the swim, efficiency, not aerobic fitness, will account for 90% of performance.
I surmise that your swim coach probably gives shorter repeats, because that’s what they’re most familiar with from having a great deal of swimming experience. It makes even more sense for triathletes because it’s the perfect way to train faster and easier.
For example, let’s compare a continuous 20min swim with a set of 10 x 100m repeats: you would likely swim 5-10% faster with the same, or perhaps less, effort on the shorter repeats. You’d almost certainly maintain a higher level of efficiency (swimming that pace in fewer strokes) on the shorter reps.
Rather than longer swims, I suggest you personalise the coach’s sets by striving to swim your current practice pace more easily and efficiently, and more consistently. Here are a few ideas for getting more value from a common set such as 10 x 100m:
Experiment with efficiency-improving techniques – align your head and spine and kick less.
Count strokes – Can you swim the same pace in fewer strokes, paying attention to the above focal points?
Complete each rep with as little time variation as possible, and keep a consistent stroke count.
The enhanced purpose and focus of these practice goals should become their own reward, but you should also find yourself swimming faster with less effort within weeks