Setting cliches like “pain is weakness leaving the body” amongst others aside, the human body is an amazing creation. We feel tired when we over-exert ourselves. Basically it is your body telling you “hey! I need some rest” so, if you rely on caffeinated energy drinks to give you the motivation/propulsion to go, then in my personal oppinion you’re not giving your body the rest it needs.

Here’s my my personal view on this. Most fitness trainers and coaches try to develope vascularization in the athlete they are coaching in order to facilitate the movement of:
1. oxygen and fuel to the muscles/tissues
2. carbon dioxide and other metabolites from muscles/tissues
3. nutrients needed to heal the body
4. waste products after the workout from the tissues

In order to develope the vascularization the body needs rest and plenty of it. How does you average energy drink affect this process?

1. being “over-alert” decreases your recuperation time
2. caffeine causes vaso constriction (blood vessles get narrower)
3. caffeine also is a diuretic (you lose not only water which will lead to dehydration, but also the electrolytes and minerals the body needs such as magnesium, calcium, sodium, phosphorus and potassium)
4. with all the stimulants in those drinks you will lose the ability to relax your muscles well enough to facilitate recuperation.

Back to the recuperation and rest subject. Decreased rest can lead to cardiovascular problems, not only with cholesterol, arteriosclerosis and such but failure of your natural “pacemaker” of your heart. I saw this happen to a guy I know, he had a heart attack and was resuccitated twice during an all out anaerobic threshold run workout. When the doctors did the artey bypass to implant the pacemaker they noticed how clean his arteries where. He was a health nut…which kept his cholestrol low and blood vessels clean, but what we think it is because he did not partake in needed recuperation he ended up with a sinoatrial node failure (meaning the doctors had to implant an artificial pacemaker in his chest), he led a very rest deprived lifestyle.

Brings me to the end of my answer, hope you take care of your recuperation as well as you are taking care of your active lifestyle and nothing beats proper nutrition, hydration and rest.