My Zone 2 training rides are generally about 3 or 4 hours. I do not eat during the ride, but include a cafe stop for about 30 mins, which includes tea and cake. After the cafe stop, there are two clear and consistent changes; my average heart rate will be higher for the remainder of the ride and my average watts will be lower. The ride also feels more difficult, even though I’m doing lower watts in similar terrain. It is clearly evident on the lower graph of the power page of my ride today, where my cafe stop occured at 2h56m: Intervals.icu
Does anyone know why these changes may occur? Is it a common phenomena? I’d be interested to learn what is going on inside to cause these changes. Many thanks for any help.
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Two guesses (which are not uncommon I think):
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Your body needs to digest the cake. This increases the heart rate.
(I don’t say you shouldn’t eat any more cake). -
Your muscles gets tired after some hours. That decreases the average power for the same RPE. You may could delay this if you eat something easy to digest during your ride.
It’s different for diff ppl so answer is gonna be “it depends”
Maybe the Higher HR + lower watts is your body telling you it wants to stay longer there and perhaps have another cake. (Purely conjecture)
But some meals does make it such that more blood is needed to digest the food. You don’t see pro riders eating meals on the bike. Just easily digestible and quick carbs.
I myself experienced this when I ate rice + meat dish at a stop. Felt sluggish afterwards and also bloating. Can’t push.
Perhaps you can monitor and determine what you body likes/dislikes.
You could try stopping and not eating cake, or not stopping at all, and then monitoring what your power and HR do.
Basically what @R2Tom says + 2 additional reasons. The weight/factor of each points depends per person.
Rebooting the Body – During a break, your body goes into a sort of “rest mode.” Your blood circulation slows, your muscles cool down, and your body reduces the production of certain performance-enhancing chemicals like adrenaline. When you start again, everything has to start all over again, which temporarily reduces your efficiency.
Accumulating Fatigue – Although a break helps you recover, the overall fatigue from the ride can still take its toll. Your body may have trouble returning to its previous performance level, especially if you’ve already expended a lot of energy.
Changes in Heart Rate Regulation – During a break, your heart rate slows down, but once you start cycling intensively again, it rises relatively quickly. This can be an indication that your cardiovascular system needs some time to efficiently pump oxygen to your muscles again.
Food and Hydration – Eating or drinking during a break can have an effect on your performance. Food requires energy to digest, which can temporarily compromise muscle effort. Too much fluid can also suddenly lead to a feeling of fullness, making your effort feel harder.
My own experience after longer rests/breaks (without cake) is that I really need longer time to warm up again. When starting a ride, I have enough of 5 min warm-up to reach performance/efficiency and I can maintain that almost the whole ride.
When I had a groupride where a longer break is common, I need a considerable longer amount of time to warm-up again. Really like 20min or so in low z2 state before I could get back to pre-break performance. My fellow riders had considerable less issues with restarting. Although they need much longer warm-up at start than I do.
I deepdived once into this observation and basically found 3 reasons that differ between persons.
Muscle recovery and fatigue – If your muscles are activated quickly in the initial phase, this can mean that your body is relatively efficient in mobilising energy and blood flow. However, after a break, this efficient system can react more slowly because your muscles and nerves have been more ‘off’, while your fellow cyclists naturally have a longer activation process and have remained somewhat active after the break.
Metabolic variation – Your metabolism can respond differently to rest. Some athletes have a faster recovery and switch quickly between exertion and rest, while others experience a slow start-up after a break because their body has to switch from ‘pause mode’ to ‘performance mode’.
Nervous system and blood circulation – Your nervous system (which keeps you active and alert) can be more suppressed after a break in you than in others, which means that you need a longer time to function optimally again. Your blood circulation has to speed up again, your muscles have to ‘warm up’ again and this takes time.
To prevent you could either do shorter breaks or try to stay a bit more active during the break. And otherwise you just need a slower start after breaks and do a long warm-up for 2nd part of the ride.
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What you’re noticing is a pretty common response to a long Zone 2 ride with a mid-ride stop and no fuelling beforehand. After 3 hours, your muscle and liver glycogen are likely running low. The tea and cake help a bit, but digestion and absorption take time—so the fuel isn’t available right when you get back on the bike.
During the stop, your body shifts into parasympathetic “rest and digest” mode, and blood flow gets redirected toward the gut. When you restart, your heart has to work harder (higher HR) to maintain output, but your muscles aren’t firing as efficiently—so power drops and perceived effort rises. Cooling off and a bit of muscle stiffness also contribute.
This is why a steady intake of 40–60g carbs per hour from the start and keeping stops under 10–15 minutes usually leads to a smoother ride.
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Higher temperatures where the bike is parked, if not compensated with temperature algorithms/manual zeroing= lower watts compared to zeroing at colder temperatures. The inverse is a know “trick” among Zwifters.