Dose response effects of a caffeine-containing energy drink on muscle performance: a repeated measures design

Background: Energy drinks have become the most used caffeine-containing beverages in the sport setting. The aim of this study was to determine the effects of two doses of a caffeine-containing energy drink on muscle performance during upper-and lower-body power-load tests. Methods: In a randomized order, twelve active participants ingested 1 and 3 mg of caffeine per kg of body weight using a commercially available energy drink (Fure (R), ProEnergetics) or the same drink without caffeine (placebo; 0 mg/kg). After sixty minutes, resting metabolic rate, heart rate and blood pressure were determined. Then, half-squat and bench-press power production with loads from 10 to 100% of 1 repetition maximum was determined using a rotator encoder. Results: In comparison to the placebo, the ingestion of the caffeinated drink increased mean arterial pressure (82 +/- 7 < 88 +/- 8 approximate to 90 +/- 6 mmHg for 0 mg/kg, 1 mg/kg, 3 mg/kg of caffeine, respectively; P < 0.05) and heart rate (57 +/- 7 < 59 +/- 8 < 62 +/- 8 beats/min, respectively; P < 0.05) at rest in a dose response manner, though it did not affect resting metabolic rate. While the ingestion of 1 mg/kg of caffeine did not affect maximal power during the power-load tests with respect to the placebo, 3 mg/kg increased maximal power in the half-squat (2554 +/- 167 approximate to 2549 +/- 161 < 2726 +/- 167 W, respectively; P < 0.05) and bench-press actions (349 +/- 34 approximate to 358 +/- 35 < 375 +/- 33 W, respectively; P < 0.05). Conclusions: A caffeine dose of at least 3 mg/kg in the form of an energy drink is necessary to significantly improve half-squat and bench-press maximal muscle power.