PURPOSE: The purpose of the present study was to examine the effects of acute doses of a thermogenic, pre-workout supplement on fat oxidation rates during moderate- intensity treadmill running in females.
METHODS: Twelve aerobically-trained females (mean ± SD: age = 25.3 ± 9.4 years; body mass = 61.2 ± 6.8 kg) volunteered to visit the laboratory on four occasions. For the first visit, each subject completed an incremental treadmill test to exhaustion to determine their ventilatory threshold (VT) using a metabolic cart. On the second visit, each subject consumed a standardized meal following overnight fasting (8 hours) 30 minutes prior to ingestion of one (S1) or two servings (S2) of the supplement or placebo (P). One serving of the supplement contained caffeine anhydrous (150 mg), beta alanine (1600 mg), arginine AKG (1000 mg), as well as tyrosine, L-carnitine, green coffee bean extract, and velvet bean extract at unspecified quantities. The placebo was a non-caloric mix that was matched for flavor and consistency. Thirty minutes post-ingestion, the subjects performed a 30-minute constant-velocity treadmill run at 90% of their VT with ventilatory parameters expressed as 5-min averages. The subjects then returned to the laboratory for their third and fourth visits to ingest the remaining conditions (S1, S2, or P) and underwent the same testing procedures (including time of day) as the second visit. A two-way ANOVA with repeated-measures was used to compare the rates of fat oxidation among the conditions (S1, S2, P) at the common time points (5, 10, 15, 20, 25, 30 min) of the 30-minute run.
RESULTS: For the rates of fat oxidation, there was no significant (P > 0.05) condition x time interaction or main effect for condition, but there was a main effect for time. Specifically, the marginal means (collapsed across conditions) for fat oxidation rates were significantly (P < 0.05) greater at 5-min (0.35 ± 0.20 g·min-1) and 30-min (0.35 ± 0.16 g·min-1) than 10-min (0.28 ± 0.13 g·min-1), 15-min (0.29 ± 0.13 g·min-1), 20-min (0.28 ± 0.14 g·min-1), and 25-min (0.31 ± 0.15 g·min-1).
CONCLUSIONS: The present findings indicated that one or two servings of the pre-workout supplement had no significant effect on rates of fat oxidation during 30 minutes of moderate-intensity treadmill running in aerobically-trained females when compared to placebo.