It all depends on the nature of the session as to how hard you want to work. The longer the reps, the slightly slower the pace will be. Or if doing hills, focus on RPE rather than pace. But you always want to be working hard to ensure you make the necessary gains.
It’s said that 1 minute of swimming has the same benefit as 1 minute of running. So a nice 45 minute swim replaces an easy 45 minute run and takes away any impact. Ideal if you are struggling a little with injury.
If you have an accurate heart rate, then use that as your main data to determine pace, if not RPE is the best option. Hills are always going to cause them to go too high, unless you are super fit. Finish off with some strides.
