Across all studies, the mean change in running performance in events ranging from the 400 m to the marathon was equal to 1.7 ± 2.7% (range: −1.6 to 10.2%). Performance improvement was greater (4.1 ± 4.4%) in studies in which CHO was ingested vs. caffeine (1.1 ± 0.4%) or buffers such as sodium citrate (0.3 ± 1.7%) or bicarbonate (1.5 ± 1.1%). Fifteen studies showed improved performance (>0.5% vs. placebo) with ergogenic aid ingestion, 6 showed no difference (0.5 to −0.5%), and 2 showed clear negative effects (more than −0.5%). It is important to note, however, that every CHO study was conducted at distances longer than 15 km. Therefore, CHO ingestion would likely have a larger ergogenic effect during these events because of their duration (>1 hour) and different metabolic demands. Additionally, 2 studies (10,54) were characterized by different environmental conditions between trials, which could have further altered performance.
Studies involving alkalizing agents administered the dosages either in a flavored solution (n = 6) or in capsules (n = 4). The dosages of sodium bicarbonate ranged from 0.3 to 0.4 g·kg−1, whereas the dosages for sodium citrate were equal to 0.5 g·kg−1. For carbohydrate, all studies except one evaluated carbohydrate-electrolyte beverages. The other study (10) evaluated carbohydrate gels (82 g). The carbohydrate concentration in these beverages ranged from 5 to 8%. Ingestion protocols for the CHO trials widely varied. Most studies provided a pre-exercise bolus of 0.5–1 L. Participants were offered serial feedings in all studies, generally at 15- to 20-minute intervals and in amounts equal 0.5–0.8 L·h−1. In the study with the CHO gels, the gels were ingested at 7 and 14 km of a 21.1-km race (10). Caffeine dosages ranged from 2.1 to 9 mg·kg−1. Significant improvements in performance were evident at dosages between 2.5 and 5 mg·kg−1, which corroborates current evidence (18).
The purpose of this systematic review was to evaluate the effects of commonly used ergogenic aids (alkalizing agents, caffeine, and carbohydrate) on middle- and long-distance running performance. Only studies with a time-trial component were included because this protocol is more valid in detecting treatment effects (25) and also more applicable to athletic performance. We also tried to analyze studies with trained and fit participants, but because not all studies reported this, participant fitness and experience with running were difficult to quantify.
In addition to the fatigue caused by acidosis, fatigue in longer middle distance events (3,000–5,000 m) is caused by a complex interaction of physiological and psychological systems (7). In conditions of high heat stress, thermoregulation and overheating may also play a role (1). Two ergogenic aids whose effects have been tested during 3- and 5-km performance are sodium citrate and caffeine, yet data are equivocal. Sodium citrate has similar metabolic benefits to sodium bicarbonate but may elicit less GI discomfort (46). Nevertheless, sodium citrate is likely not as effective as sodium bicarbonate because of increased water retention, and increased citrate concentrations may inhibit phosphofructokinase, which could reduce generation of adenosine triphosphate through glycolysis (26). Previous data show that sodium citrate improved 3-km performance (−10 seconds, 1.7%) in a field study (52) and treadmill 5-km performance (−30 seconds, 2.7%; 38) but did not alter 1,500-m or 5-km performance in field studies (38,39). Others (40) demonstrated that consuming 5 mg·kg−1 of caffeine significantly improved 5-km performance in well-trained (−10 seconds, 1.0%) and recreational runners (−11 seconds, 1.1%).
The authors acknowledge the difficulties of testing runners in laboratory and field settings. Highly trained runners are a notoriously difficult population to study because many are unwilling to alter their training schedules to accommodate physiological testing or have little desire to run for extended periods on a treadmill. Most field studies have not adequately categorized the current fitness level or training volume of their subjects (6,40); therefore, it can be difficult to interpret an author’s definition of “well trained” vs. “recreational” or “sub-elite/elite.” Additionally, offering nutritional counseling to recreational runners based on data from elite athletes is impractical because both groups have different nutritional needs and genetic profiles. Therefore, V[Combining Dot Above]O2max values, training history, personal bests, and other demographic data should be reported by scientists to more precisely represent subjects’ fitness levels and typical training regimes. In this way, the coach can best interpret the data presented and apply it to their own athletes.
Finally, gender differences must be considered. Nearly 55% of the participants in road races in the United States in 2010 were women (51). However, in this review, only ∼12% of the total subjects in all studies were women (n = 51 vs. 385 men). With the population of female runners expanding, scientists need to examine the effects of various ergogenic aids on running performance in women. Although most research done in men can be extended to women, some qualifications and cautions must be considered because of the structural, hormonal, and metabolic differences between men and women.
In summary, more research is needed on female runners and recreational runners, who represent the majority of competitors in road racing. “Poly-supplementation” (the use of multiple supplements to attain a synergistic effect) remains a relatively unexplored area of ergogenic aid research. Research in this area is important because combining supplements such as caffeine and carbohydrate is a common practice for endurance athletes.
Current research regarding acute nutritional supplementation is constantly evolving. It is important that coaches and athletes become aware of the importance of nutrition in enhancing athletic performance. All substances examined in this review are widely available and presently legal in international and collegiate competition (except caffeine levels > 15 μg·mL−1 detected within urine in the NCAA).
At present, the majority of existing data can be applied to male and, with some qualifications, female runners, who are trained (>3 h·wk−1). Little is known about the nutritional practices of lesser-trained runners before and during competition, and thus, the data discussed here may not be applicable to them. Ultimately, before an athlete and coach decide on a particular supplement plan for competition, it is important to develop and use such a plan in practice, so as to identify the best techniques to increase individual performance.
The authors thank the reviewers for their thoughtful comments that helped improve the manuscript. The authors declare no conflicts of interests or funding for this study.
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