Concept 2 users probably all know this but one of the good things about ’em is that it is not hard to set up programs (on the little monitor that comes on the gadget) which will set you a course of intervals…you get to decide how long the hard and relaxed stretches are. That is a real blessing. It is SO hard to do self-administered intervals…and the Concept 2 helps a lot. No reason not to do the same thing on a real or stationary bike, but it’s a help to have it built in.
The real answer is a trainer – with a stopwatch in one hand and a knout in the other. But that gets expensive. Also, hate that damned knout.