When doing cardio preasure and rate rise gradually. Energy drinks make very sharp rise to level which almost always above optimal even for trained people. There is also another problems that body tries to fight unnatural heart rate rise and that might lead to heart arest.

Part of the reason is that during exercise, vessels leading to muscles also dilate, so the blood has somewhere to go and there is less stress on the cardiovascular system than if heart rate is increased in vacuum.

When doing cardio the body release speacial hormones that promote growth in muscles.

Also as was said, the body adapt to the rosing stress levels on the blood system

Besides the other answers, it also has to do with duration.

When you're doing cardio exercise, do you go for 5 hours non-stop with zero breaks? Energy drinks raise your heart rate constantly, for hours. If jogging for several hours straight sounds like "too much exertion to be beneficial and into the realm of possibly also damaging" well that's why elevating your heart rate for a whole day with energy drinks is possibly damaging too.

Could you, please, explain the ways in which the body fights an unnatural heart rate rise that might lead to heart arrest?

All your organs are autonomous. They rarelly need extra instruction from brains. Heart synapsis are affected by chemicals in energy drinks and treat them as instruction to work harder. Brain detect abnormal heart rate increase and start sending signals to hear to slow down because there is nor reason for wasting energy. Conflicting signals can cause arrhythmia and sever arrhythmia can lead to heart arest. While hear arest is an extreme case, arrhythmia by itself is not something heart should expirience regulary.

For most questions in biology when you ask "why is X ok but not Y" the answer is usually always scale. Because Y is too much.

When you exercise your body will tell you when you are pushing it too far, when your heart rate has been too high for too long. When you have to stop and take a breather for a minute, your heart can also take a rest and the heart rate can come down.

Energy drinks however stimulates the heart to go full throttle for hours, with no breaks or rests. Often with no purpose or gain. It's too much

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