Nutritional supplementation is a common practice among athletes, with creatine and caffeine among the most commonly used ergogenic aids. Hundreds of studies have investigated the ergogenic potential of creatine supplementation, with consistent improvements in strength and power reported for exercise bouts of short duration (≤30 s) and high intensity. Caffeine has been shown to improve endurance exercise performance, but results are mixed in the context of strength and sprint performance. Further, there is conflicting evidence from studies comparing the ergogenic effects of coffee and caffeine anhydrous supplementation. Previous research has identified independent mechanisms by which creatine and caffeine may improve strength and sprint performance, leading to the formulation of multi-ingredient supplements containing both ingredients. Although scarce, research has suggested that caffeine ingestion may blunt the ergogenic effect of creatine. While a pharmacokinetic interaction is unlikely, authors have suggested that this effect may be explained by opposing effects on muscle relaxation time or gastrointestinal side effects from simultaneous consumption. The current review aims to evaluate the ergogenic potential of creatine and caffeine in the context of high-intensity exercise. Research directly comparing coffee and caffeine anhydrous is discussed, along with previous studies evaluating the concurrent supplementation of creatine and caffeine.
Eric T. Trexler and Abbie E. Smith-Ryan
Eric T. Trexler, Katie R. Hirsch, Bill I. Campbell, and Abbie E. Smith-Ryan
The purpose of the current study was to evaluate changes in body composition, metabolic rate, and hormones during postcompetition recovery. Data were collected from natural physique athletes (7 male/8 female) within one week before (T1) competition, within one week after (T2), and 4–6 weeks after (T3) competition. Measures included body composition (fat mass [FM] and lean mass [LM] from ultrasongraphy), resting metabolic rate (RMR; indirect calorimetry), and salivary leptin, testosterone, cortisol, ghrelin, and insulin. Total body water (TBW; bioelectrical impedance spectroscopy) was measured at T1 and T2 in a subsample (n = 8) of athletes. Significant (p < .05) changes were observed for weight (T1 = 65.4 ± 12.2 kg, T2 = 67.4 ± 12.6, T3 = 69.3 ± 13.4; T3 > T2 > T1), LM (T1 = 57.6 ± 13.9 kg, T2 = 59.4 ± 14.2, T3 = 59.3 ± 14.2; T2 and T3 > T1), and FM (T1 = 7.7 ± 4.4 kg, T2 = 8.0 ± 4.4, T3 = 10.0 ± 6.2; T3 > T1 and T2). TBW increased from T1 to T2 (Δ=1.9 ± 1.3 L, p < .01). RMR increased from baseline (1612 ± 266 kcal/day; 92.0% of predicted) to T2 (1881 ± 329, 105.3%; p < .01) and T3 (1778 ± 257, 99.6%; p < .001). Cortisol was higher (p < .05) at T2 (0.41 ± 0.31 μg/dL) than T1 (0.34 ± 0.31) and T3 (0.35 ± 0.27). Male testosterone at T3 (186.6 ± 41.3 pg/mL) was greater than T2 (148.0 ± 44.6, p = .04). RMR changes were associated (p ≤ .05) with change in body fat percent (ΔBF%; r = .59) and T3 protein intake (r= .60); male testosterone changes were inversely associated (p≤ .05) with ΔBF%, ΔFM, and Δweight (r=-0.81–-0.88). TBW increased within days of competition. Precompetition RMR suppression appeared to be variable and markedly reversed by overfeeding, and reverted toward normal levels following competition. RMR and male testosterone increased while FM was preferentially gained 4–6 weeks postcompetition.
Ashley A. Walter, Abbie E. Smith, Trent J. Herda, Eric D. Ryan, Jordan R. Moon, Joel T. Cramer, and Jeffrey R. Stout
The purpose of this study was to examine the effects of 5 d of creatine (Cr) loading on the electromyographic fatigue threshold (EMG FT) in college-age men. Sixteen men (age 22.4 ± 2.6 yr, height 177.4 ± 6.8 cm, weight 79.5 ± 10.6 kg; M ± SD) participated in this double-blind study and were randomly placed into either placebo (Pl; 10 g of flavored fructose powder per packet; n = 8) or Cr (5 g dicreatine citrate plus 10 g of flavored fructose powder per packet; n = 8) loading groups. Each participant ingested 1 packet 4 times/d, totaling 20 g/d for 5 days (loading). Before and after loading, each participant performed a discontinuous cycle-ergometer test to determine his EMG FT, using bipolar surface electrodes placed on the vastus lateralis of the right thigh. Four 60-s work bouts (ranging from 200 to 400 W) were completed. Adequate rest was given between bouts to allow for the participants’ heart rate (HR) to drop within 10 beats of their resting HR. The EMG amplitude was averaged over 5-s intervals for each 60-s work bout. Resulting slopes from each successive work bout were used to calculate EMG FT. A 2-way ANOVA, Group (Cr vs. Pl) EETime (pre vs. post), resulted in a nonsignificant (p > .05) interaction for supplement and time. In addition, a significant increase (p = .009) in weight was observed in the Cr group. These data suggest that there was a minimal influence of Cr loading on EMG FT for the participants in this study.