When you stand up from the saddle, your heart rate will likely increase (unless you’re Tom Scotto!). Even if power remains the same (same resistance, same cadence), the cost of standing up is higher than sitting. This is reflected as an increased heart rate. Of course, the more fit you are, the less of an impact standing will have. But, if you spend a lot of time out of the saddle you will likely be spending more energy for the effort.
I had an opportunity to highlight this to my class yesterday in a very revealing way. It’s a great technique to point out the impact that standing has on the cardiovascular system, and then show how to bring that heart rate back down once you return to the saddle while still working at the same effort as prior to standing. For outdoor cyclists, this revelation is critical (and possibly unknown by many cyclists), and the knowledge gained can help improve recovery while working. This in turn will improve overall climbing endurance as you work to reduce the effects of standing.
My profile consisted of five sets of muscular endurance climbing repeats of 6 to 9 minutes, with cadence at the high 60s on up to 80 rpm. Most of the effort was in the saddle but for each repeat, we did two short standing segments of 30 seconds.