IMHO, most energy drinks on the market are krap (sic). I am referring to Red Bull, Monster and others that rely primarily on
sugar &
caffeine (with a bit of Taurine and small amounts of a couple of B vitamins).
However, I've had excellent results with
5-Hour Energy,
6 Hour Power and
ProEndorphin.
No sugar in these products and only a moderate amount of
caffeine = ~35mg/oz for most of them & only 35 mg for a full (8oz) serving of ProEndorphin. However, my new favorite is Choco Energy from Now (Foods). It leaves all the others in the dust:
<-- select for more info
I like the 5-hour type drinks where the chief ingredients are B6 and B12. I don't like the typical Monster or Red Bull type drinks. Although I have sipped on these for a long time while driving long distances.
I don't think they'd be good for tennis (for me). Too jittery and too big a crash when they do burn off.
No jitters at all for the no-sugar, moderate caffeine products, like 5-Hour and the others I mentioned above. Note that these products contain more than just B6 and B12 for their effect. The
amino acids in the formula are fairly effective if the product is consumed on an empty stomach (or, at least, in the
absence of competing
protein). Most of these types also contain some other B vitamins as well as Glucuronolactone and DMAE or some choline ingredient. I believe that Choc Energy gets much of its superior effects from D-Ribose and various constituents of cocoa (chocolate) in addition to its generous B12 levels (and a few other constituents).