In the grad scheme of things, I think that coasting versus lightly pedaling is rather inconsequential in terms of the broader energetic and fuel savings.
With the goal of trying to arrive to the finish as fresh as possible, your goal is to conserve energy in terms of glycogen. Fatigue is closely tied with the amount of muscle glycogen you have and can be prolonged with glucose intake (as we all know). When you lightly pedal, you aren’t expending energy whereas lightly pedaling you maybe be utilizing primarily fats (due to relatively low VO2 requirement) and to a lesser extent glucose and glycogen.
We can get into the details further and say that each time you stop pedaling and rest for a period of time (in the realm of 5+ minutes, which is not really happening during race situations, maybe during a long decent??) there is a “restart cost”. That is, there is primarily anaerobic demand to produce the power until the aerobic system ramps of sufficiently to better support energy production. During this period glycogen and the PCr system will be used more aggressively. However, in reality during a race, you’ll stop pedaling for maybe 10 seconds (?), unless it is a descent, at which point you’ll start pedaling again. So these efforts are really aerobic in nature and the proportion of fuel utilization will be dictated by the intensity of the effort(s).
In terms of lactate, the rate of lactate uptake and utilization will be dependent on the several factors including the number of transporters in the muscle and mitochondria and the ability to oxidize lactate. The key part here is that lactate has an associated H+ ion, which decreases the pH in your muscle and blood. Your ability to shuttle and neutralize the excess H+ ions is closely related to your ability to clear lactate. While pedaling, you are continuing to maintain greater rates of blood perfusion throughout your muscles, so this can help clear lactate and H+ shuttling them to other tissues where they can be utilized. In terms of oxygen levels and recovering faster with no-pedaling, I am not sure I have heard that, but would like to see the data.
You could get into the nitty gritty and calculate the amount of kJ saved from lightly pedaling versus no pedaling. I think you will find that the energy savings are rather small. Focusing on fueling, race positioning, etc. will be key. Essentially this boils down to do what you need to do to save your “fuel” (glycogen), for when you need it most. If that means pedaling less, do that!
