The primary purpose of this study was to examine the acute effects of one versus two doses of a multi-ingredient pre-workout supplement on energy expenditure during moderate-intensity treadmill running. In addition, our second aim was to investigate the responses of associated metabolic factors (i.e. substrate utilization, measures of gas exchange), perceived exertion, and resting cardiovascular variables with one and two doses of the pre-workout supplement.

This study utilized a randomized, double-blind, placebo-controlled, within-subjects crossover design (Figure 1). Each subject was required to visit the laboratory on five occasions with 72-96 hours between sessions. During the first laboratory visit, each subject performed an incremental test on a treadmill to familiarize the subjects with the testing procedures. For the second laboratory visit, each subject performed an incremental treadmill test to exhaustion to determine their ventilatory threshold (VT). The third laboratory visit was completed in the morning (06:00-09:00) and required subjects to consume a standardized meal after fasting overnight (8 hours) and sat quietly for 30 minutes before baseline heart rate and blood pressure values were recorded. The subjects were then randomly assigned to ingest the supplement (one or two doses) or placebo and sit quietly for another 30 minutes. The ingredients of the supplement (Cellucor, Bryan, TX) are provided in Table 1. The placebo was non-energetic and controlled for similar appearance and taste. At the 15-minute and 30-minute post-ingestion periods (of the pre-workout supplement or placebo), resting heart rate and blood pressure were recorded for a second and third time, respectively. Subjects then performed a 30-minute constant-velocity treadmill run at 90% of their VT. The subjects then returned to the laboratory for their fourth and fifth visits to ingest the remaining substances (1-dose, 2-dose, or placebo) and undergo the same testing procedures (including time of day) as the third visit. Each subject recorded 2-day food logs (MyFitnessPal, Inc., USA) prior to each laboratory visit.

Inclusion Criteria:

• ran ≥ 16 km per week

Exclusion Criteria:

• (i) history of medical or surgical events, including cardiovascular disease, metabolic, renal, hepatic, or musculoskeletal disorders; (ii) use of any medication; (iii) use of nutritional supplements; (iv) habitual use of caffeine (≥ one cup of coffee or caffeinated beverage per day); or (v) participation in another clinical trial or investigation of another investigational product within 30 days prior to screening/enrollment.