Caffeine reduces RPE, but at what cost?

I’m a fan of caffeine for racing or hard training days. I see significant reduction in RPE and will typically do 400+ mg of caffeine via gels, usually taken during the earlier parts of a race. It doesn’t help everyone, but there are a lot of studies that show these benefits.

Here is my concern/question - Caffeine pushes my heartrate up ~8 beats per minute at most power levels. I think a rise in HR from caffeine is pretty common. So, while caffeine can make a given power level feel easier, it’s happening at a higher HR. It makes me wonder if the higher HR is an important contributor to the lower RPE because it’s pushing more oxygen to the muscles, etc. Regardless of how caffeine works, it’s driving a higher HR at similar power, and I have to believe there is a physiological impact as a result. While I am never consciously aware of fatigue of my heart, I assume the body regulates this to prevent it from being overworked at some point. Is there anything to this? Any science that backs this up?

At the core, I think my question is which of the following options is better/faster and can be sustained longer:
-Riding at tempo with a high dose of caffeine - lower RPE, but running a higher HR
-Riding at tempo with no caffeine - “normal” RPE and HR

Within this question, maybe the key question is whether increased HR has a negative effect on endurance or is there no measurable cost?

I’m not debating the value of caffeine in certain events. If I was doing a 40k TT or really any event under a few hours, I think the reduced RPE can help push performance to the max. For longer events, I question whether the reduced RPE ultimately comes at the cost of reduced endurance. Particularly early in a long race where I don’t need RPE to be lowered until late in the race.

I’m racing Leadville in a couple weeks and I’m locked in on my caffeine plan, but it’s definitely got me thinking about how it might help and hurt for a long event like this.

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I’m pretty sure it is strictly better to be stimulated as long as the higher heart rate doesn’t cause heart issues for you. Heart rate doesn’t really mean much bc it can be affected by mental factors like excitement, anxiety, etc. Your stated avg increase of 8bpm when caffeinated sounds like you are very caffeine-sensitive. You better ride your heart out so you can sleep! Lol

If they were legal, pro athletes would almost surely use more hardcore stimulants. So that prob answers your question to caffeine-up!

It’s interesting how there are so many attempts to separate the “central” from “peripheral” effects of training and performance, as if caffeine needs to have a physiologic effect on muscle biochemistry or function to change performance. It is entirely possible that the effects of caffeine are solely due to the effect it has on the CNS. Just because it is a CNS effect makes it no less powerful and no less limiting/enabling. Separating these two is kinda pointless IMHO.

That being said, just like the rest of life, caffeine is a tool that we can use to temporarily increase our work capacity. It doesn’t change the overall amount of stress you can sustain, it just makes it more tolerable…for a time. Staying “in the red,” whether with caffeine or without it, will have the same end destructive results.

Linking the below less as answers to you, OP, and more as additional resources for further the discussion in the thread.

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After a quick google search. Caffeine doesn’t alter carb or fat metabolism during exercise.

Just one study: Caffeine ingestion does not alter carbohydrate or fat metabolism in human skeletal muscle during exercise

From most of what I’ve read. The main overview is that caffeine does not give you super powers. You can’t out ride your physiology. But it can reduce RPE and make efforts more tolerable. So when you might typically stop pedaling after 50min at FTP now maybe you can go to 55 or 60min. However, you do have to be a bit careful because even though the RPE is reduced you still incur the same metabolic cost for hard efforts and you may pay for that later in the race if you are not careful.

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I think that is the crux of the issue. I have to believe there is a cost to my HR running higher, so am I better off not taking any caffeine early in long races? If I can ride tempo for the first 3+ hours of a long race at a lower HR and higher RPE (without caffeine), shouldn’t that position me to be better (physically) for the balance of the race? I think you could argue that the use of caffeine early is actually burning unneeded energy (extra heart beats) even though it feels easier. There may be other things in play besides the HR that balance this out, but not sure.

My current plan for leadville is to do 100mg at the start (just to wake up), 200mg at the beginning of the big columbine climb (~3 hours in) and another 200mg at the start of powerline climb (~6+ hours in). I’m probably not going to change things up at this point because I’ve had good luck with this approach in the past, but I think I could do the first 6 hours at same pace (higher RPE) without caffeine. It’s got me thinking maybe just defer the caffeine until I start struggling to make my target power.

That’s the part I’m questioning. If my HR is higher for the same power, the metabolic costs at a given power level are arguably higher with caffeine (just feel easier). That’s fine for a 1 hour TT, but maybe worth consideration for longer events.

But is this true? Is metabolic cost tied to HR or to power output? They measured HR during the study I linked and they saw a 5-6bpm increase from non-caffeinated to caffeinated but still no relevant change in carb or fat utilization.

Your output in KJ doesn’t change when you have a higher or lower HR. It’s a function of the wattage and time. You still need to fuel the same to replenish.

But your output in KJ is not directly tied to the physiological load required to produce it. So, depending on how you are producing X watts, the efficiency can vary. If you are producing 250 watts at a HR of 130, I think you could argue that it’s doing it more efficiently compared to producing 250 watts at a HR of 140. The leg muscles might be doing the same work, but I assume the heart is burning a few more calories at the higher rate and will eventually fatigue quicker. If the higher HR is contributing efficiencies elsewhere, maybe it’s a wash, but otherwise it seems like wasted movement. Maybe when the heart beats faster, it isn’t beating as hard and the work balances out, I don’t know.

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