The scientists had their 10 subjects perform a critical velocity (CV) in order to "quantify the relationship between total running distance and time to exhaustion (TTE), yielding aerobic (CV) and anaerobic parameters (anaerobic running capacity [ARC])". One group received the preworkout supplement (ACT) the other received a placebo (PL) before they completed the test at 110% vs. 90% and 105% vs. 100%, on separate occasions. Their findings are quite straight forward:
The ACT elicited a 10.8% higher ARC (P = .02) compared with the PL, whereas no difference was found in CV (0.6%, P = .38). The TTE was greater for the ACT than the PL at 110% (ACT = 125.7 ± 9.6 seconds, PL = 117.3 ± 12.6 seconds), 105% (ACT = 156.9 ± 11.0 seconds, PL = 143.8 ± 12.9 seconds), and 100% PV (ACT = 185.7 ± 10.7 seconds, PL = 169.7 ± 12.8 seconds) (P = .01-.04); but there was no difference for the TTE at 90% PV (ACT = 353.5 ± 52.7 seconds, PL = 332.7 ± 54.0 seconds) (P = .08).So if you go to your personal limit (i.e. 100% or more) you will probably benefit from investing some money in one or another of the current preworkout products. If you are an endurance athlete, though, you better spend your money on something else.