It's not my intention to use clen as preworkout (or use it at all). I was just curious if anybody used it as preworkout and how they did and what dose they used knowing that clen has a half life of about 26 hours and have a biphasic elimination that can take up to two days.
I haven't used Clen, and don't intend to (cardio toxicity concerns me). The broader issue here is that several beta-agonists have demonstrated the ability to grow muscle/cut fat (re-partitioning). They don't do it as well as most anabolic steroids but they do have an effect - which is more than you can say for most supplements. Unfortunately, the stimulant effects are too much for some people, although that doesn't seem to stop them from loading up on over-caffeinated pre-workouts, sometimes laced with dirty stims like Yohimbe.
To really be on top of your game, get a good night's steep and have your blood sugar steady going into training. Moving up a notch, 3 grame of L-tyrosine, DMAE (di-methyl amino ethanol) as a source of choline/acetylcholine and 2 tablespoons of lecithin pre-workout can increase vigilance. Generic caffeine tabs (200mg, "Jet Alert" at Walmart) are a solid addition as a "driver". You get 90, 200mg tabs for less than $5. Hell of a lot more reasonable than the over-priced 1,3,7-Trimethylpurine-2,6-dione (oops, I mean caffeine) pre-workouts most kiddies use.
The ideal pre-workout would be a non stimulant that increases vigilance and focus, such as Modafinil/Provigil. Unfortunately, Modafinil is Rx only in the United States, illegal without a prescription. Fortunately, it's direct precursor (Adrafinil) is not. Takes about 45 minutes to kick in, but has almost the same effect.
It can be liver toxic though, so best to use only occasionally. To be safe, consider dosing along with 1.5 grams of N-Acetyl-Cysteine, 300mg of the R isomer of Alpha Lipoic Acid or a gram or so of Curcumin. TUDCA is the best liver protector (single ingredient, anyway), but is probably over-kill in this case...