Abstract
PURPOSE: Consumption of energy drinks by both recreational and competitive athletes, as well as the general population, has increased dramatically since the late 1980's when these drinks were first introduced to the market. The primary ingrethents in most energy drinks include caffeine (CAFO in various forms, taurine (TAUR), B vitamins, and sugar. Although several studies have examined the effect of energy drinks on endurance exercise performance, less is known regarding their effect on anaerobic exercise, particularly the sugar-free (SF) versions of these products. Therefore, this study examined the effect of a popular SF energy drink that contains CAF and TAUR to a CAF only SF drink and a placebo (PL) on upper body muscular strength and endurance. METHODS: Thirteen physically active men (mean age ± SD = 21 ± 1 yr; body weight = 87.2 ± 8.8 kg; %Fat = 9.9 ± 3.0%) who had been strength training > 3 times/wk for at least 6 mo, and who habitually consumed ≤ 50 mg/d of CAF were recruited for the study. The subjects visited the laboratory on 3 separate occasions separated by 1 wk and were instructed to refrain from alcohol, CAF, and upper-body resistance training 24 hr before testing and arrive in a fasted state (at least 4 hr after their last meal). Sixty minutes prior to strength testing, each subject received one of the following drinks in a double-blind, randomized order: A) 16 oz of a commercially available SF energy drink containing CAF (160 mg) and TAUR (2000 mg); B) 16 oz of a SF drink containing CAF only (160 mg); or C) a SF, CAF-free PL drink. The drinks were similar in taste and appearance, served in an opaque container, and consumed as quickly as possible. In the hour before strength testing, the subjects sat quietly and studied, read, or watched TV. Prior to 1RM bench press (BP) testing, each subject completed a 5 min warm-up on a treadmill or elliptical machine followed by 10 reps at 40-60% of each subject's perceived 1RM on the BP and, after 3 min rest, they performed 3-5 reps at 60-80% of their perceived maximum. The representative 1RM was recorded as the weight of the last successfully completed lift, which typically took 3-5 attempts with 5 min rest between each attempt. After determination of the 1RM, subjects rested 5 min and then completed as many reps as possible at 70% of their 1 RM to assess muscular endurance. Differences between trials for 1 RM BP and the volume load (VL = reps X load at 70% 1 RM) were identified using one-way repeated measures ANOVA (p<0.05). RESULTS: The results indicated that SF energy drinks containing CAF or CAF + TAUR had no effect on 1RM BP (118.6 ± 15.4 kg and 118.6 ± 15.6 kg, respectively) or VL (1187.7 ± 146.2 kg and 1184 ± 169.2 kg, respectively) compared to PL (1RM = 117.4 ± 15.5 kg; VL= 1146.0 ± 198.4 kg). CONCLUSIONS:Although the CAF content in the energy drinks used in the present study may be considered low when expressed relative to BW (1.8 mg/kg), the finding of no effect of the CAF containing energy drinks for 1 RM BP are in agreement with previous studies using untrained men using intakes of approximately 4.9 mg/kg. Practical Applications: These findings suggest that SF energy drinks containing CAF with or without TAUR have no effect on 1RM BP or VL in resistance trained men. [PUBLICATION ABSTRACT]