Just for the record, and in case it's important in experiment planning, caffeine isn't actually tasteless at all. has a fairly bitter and certainly easy to recognize taste dissolved in just water.

It is, however, really easy to mask in, for example, orange juice, so the taste shouldn't make the experiments hard as such. Just another design constraint to be aware of.

I'd also recommend adding some sort of n days on, m days off cycling to your tests, mostly because that's what I do and I want to take advantage of other people's research.