Running is one of the most popular forms of sport and recreation in the United States. In 2010, approximately 13 million people finished a road race in the United States: 4.7 million completed a 5-km race (3.1 miles), 1.4 million competed half-marathons (13.1 miles = 21.1 km), 1.3 million ran a 10 km (6.2 miles), and 500,000 finished a marathon (26.2 miles = 42.2 km) (50). Nutritional demands of running are widely varied, depending on the distance and the ability of the athlete. It is relatively well known that high-carbohydrate diets are important to sustain performance during the periods of high training stress. However, many acute aspects of nutrition (i.e., race-day dietary habits, energy and fluid intake during competition, ergogenic aid usage) among distance runners remain unexplored or unreported. With such a large population of runners, coaches and practitioners should be able to provide practical supplement advice to runners who seek it. Therefore, efficacy of nutritional strategies to improve running performance, tolerate increased training, and decrease occurrence of injury has become an area of interest among sport scientists.
For example, a recent case study on 3 elite marathoners reported that 16 weeks of training, during which training and nutrition habits were periodized and tightly controlled, led to performance improvements of 1.9–4.0% in the marathon (53). Additionally, the margin between a medal and no medal, or gold and bronze, is typically very small. Analysis of the last 5 IAAF World Championships for men revealed that the mean difference in performance between the first and third was 0.07% (0.53 seconds) in the 5,000 m, 0.43% (7 seconds) in the 10,000 m, and 1.2% (93.8 seconds) in the marathon. The differences in performance for a medal or a scorer/National Collegiate Athletic Association (NCAA) All-American (1st to 8th) are 2–3 times that of World Championship-caliber athletes but still quite small (∼0.2 to 1.5% in the 5,000 and 10,000 m). Consequently, identifying factors that can elicit small improvements in performance in competitive runners is merited. However, footwear, timing and record keeping, track and road surfaces, and training methods have not changed much in the past 20–25 years, with the notable exception of sport-specific resistance training (62). The field of sports nutrition, however, has widely expanded; for example, numerous sports nutrition–specific journals are now published. Many journals also publish special issues or papers that address nutrition and its role in various sports and also nutrition guidelines and position stands. Moreover, use of ergogenic aids to enhance performance is well understood and widely accepted among sports scientists and athletes.
Unfortunately, data examining the efficacy of ergogenic aids on distance running performance are relatively scarce. Most studies that address effectiveness of ergogenic aids have been conducted using laboratory-based cycling. For example, systematic review by Ganio et al. (18) evaluated effects of caffeine (CAFF) intake on endurance performance. In 6 running-based trials (4 studies), CAFF ingestion only improved running performance by 0.9%, lower than results from 21 trials (14 studies) using cycling that showed a mean improvement of 4.4%. However, there are considerable physiological differences between running and cycling (34), so the results of studies using cycling protocols cannot be easily applied to running. With performance variability in runners equal to ∼1 to 2% depending on fitness level [better trained runners tend to produce more reliable performance (23,24)], and the smallest worthwhile change in performance equal to ∼0.5% (22), it is difficult to draw conclusions from the literature regarding caffeine ingestion as a worthwhile method to improve running performance. Compared with the number of caffeine studies using laboratory cycling protocols published since 2005 (∼35 studies on PubMed and ∼30 on SportDiscus), only 3 studies in which caffeine was ingested used running-based protocols simulating competition, such as a time trial over a fixed distance rather than a time-to-exhaustion test. Because no endurance sport exists in which athletes attempt to cover the greatest distance or perform to exhaustion, these tests have minimal applicability for athletes. For the purposes of this article, distance running events were defined as middle distance (400–5,000 m) and long distance (10,000 meters marathon = 42.2 km). Performance for these events varies widely, from elite middle distance runners who cover 400 m in less than 50 seconds up to recreational runners who may take more than 4 hours to complete a marathon. It is this variability in performance that not only makes running unique but also presents challenges when interpreting data from the previous studies.
Therefore, the purpose of this article was to systematically examine existing data relating to the utility of various ergogenic aids, discuss potential limitations of the literature, and suggest directions for future research specific to distance running performance. Additionally, practical applications of the results will be presented for the coach/practitioner because often they may have limited knowledge of nutrition or are unaware of up-to-date research. For the purposes of this review, effects of acute ingestion of ergogenic aids including alkalizing agents, caffeine, and carbohydrate (CHO) on exercise performance completed by trained subjects were evaluated.
Experimental Approach to the Problem
A systematic search of numerous literature databases was conducted between July and September 2011. PubMed, SportDiscus, Academic Search, Science Direct, Medline, and other databases were searched for the following keywords: caffeine, running, time trial, performance, sodium bicarbonate, sodium citrate, carbohydrate, ergogenic aid, and field study. Studies were also identified and used from the primary author’s collection. Initially, 60 studies were identified. Attrition of studies is shown in Figure 1.
Studies were included if they consisted of trained runners completing a time trial at distances between 400 m and the marathon (42.2 km) and used a placebo-controlled design. Field and laboratory studies were included. Studies were generally conducted in a double-blind randomized order, although single-blind studies were included if the treatments were blinded to the participants or if the participants were deceived regarding the purpose of the study. Participants were required to be well-trained or recreational runners (V[Combining Dot Above]O2max ≥ 55 mL·kg·min−1 for men and ≥50 mL·kg·min−1 for women; training commitment >3 h·wk−1/35 km·wk−1).
Studies were excluded if they used an open-ended test protocol such as exercise to exhaustion or a test of endurance capacity instead of endurance performance. As stated previously, open-ended tests do not simulate sport performance. Studies were also excluded if they lacked a measure of performance (i.e., exercise was conducted at a submaximal intensity for a set time or distance), used a distance less than 400 m or longer than a marathon (42.2 km), or lacked a clear placebo/control trial.
The system of analysis used to rate each article was the Physiotherapy Evidence Database (PEDro) scale (42). This scale was developed originally to evaluate physical therapy interventions using randomized controlled trials. The PEDro scale objectively assesses a study’s internal validity and is based on an 11-item checklist with a maximum score of 10 points. Any studies with PEDro scores less than 6 were excluded from the analysis (2,18,62). As previously reported (62), we chose the PEDro scale because it has been previously validated and used in these types of reviews (18,62). Each article was analyzed and scored independently by 2 reviewers, with a third reviewer obtained if there was a discrepancy between scores. The kappa value, which indicates the level of agreement between reviewers, was equal to 0.85, similar to that previously reported for a systematic review on caffeine (18).
To determine the effectiveness of an ergogenic aid, we used an approach based on the smallest worthwhile difference of 0.5% (23). If a study showed a performance improvement greater than 0.5% with ergogenic aid ingestion, it was considered a positive effect, whereas any study with a decrement in performance of greater than −0.5% was considered a negative effect. A study showing a change in performance between 0.5 and −0.5% was considered to be unclear or have no effect.
The mean PEDro score for the 23 studies was 7.85 ± 0.70. Articles ranged from a PEDro scale score of 6.0 to 8.5 on a scale with a maximum of 10 points (Table 1). Seventeen studies were published in peer-reviewed journals and the remaining 2 studies were a master’s thesis and a doctoral dissertation. The dissertation and 2 of the published studies (3,40,56) either evaluated 2 different treatments or had 2 groups of participants and, thus, each was evaluated as 2 studies, bringing the total number of studies examined to 23. Studies are listed in chronological order by ergogenic aid in Table 1. All studies except one (15) reported some value for performance (i.e., finish time). For all studies, percentage change in performance compared with placebo or control trials was calculated. Sixteen studies were field studies conducted on running tracks or roads; the remaining studies were conducted on a motorized treadmill in a laboratory. Twenty studies used trained runners, although their exact training state is difficult to quantify because not all studies reported participants’ training history, personal best performances, or V[Combining Dot Above]O2max. Several studies also used recreational athletes, triathletes, and fit university students, whose main forms of physical activity consisted of games-type exercise several days per week. Although several studies (5,19,61) incorporated a separate control and familiarization trial in addition to placebo and experimental trials, this was not the norm. Nearly all studies were conducted using a randomized, crossover, single- or double-blind design. The 23 studies elicited a total of 55 trials with separate conditions (i.e., experimental, control, placebo) and a total of 436 subjects (51 women; 11.7% of total sample). Thirteen studies examined middle-distance running performance (400–5,000 m), whereas the remaining 10 were focused on long-distance running (8–40 km).
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 middle-distance running (400–5,000 m), metabolic acidosis and neuromuscular fatigue are detrimental to performance. Scientists have long suspected that an ergogenic aid that could induce metabolic alkalosis pre-exercise could improve buffering capacity, better maintain muscle and blood pH, and potentially enhance performance. The supplement that has been most researched in this regard is sodium bicarbonate (NaHCO3), which increases blood pH,
, and extracellular buffering capacity (11,29). This potentiates efflux of hydrogen ions and lactate from the exercising muscle into the blood, thereby allowing greater H+ ion and lactate production before muscular pH falls to fatiguing levels (28). However, sodium bicarbonate is used infrequently by athletes because of fears of gastrointestinal (GI) discomfort (11). Field studies have shown improved performance compared with control and placebo ingestion at distances of 400 (19), 800 (61), and 1,500 m (5). The optimal dose has yet to be established, but data indicated that 0.3 g·kg−1 body mass (BM) ingested with a high-carbohydrate meal and 7 mL·kg−1 flavored water 2–2.5 hours pre-competition may optimize buffering capacity with the least potential for GI distress (13). A recent meta-analysis by Carr et al. (12) estimated that 0.3 g·kg−1 BM of bicarbonate would improve mean power in a 1-minute sprinting effort by 1.7 ± 2.0%, whereas sodium citrate had no effect (0.0 ± 1.3%) (90% confidence limits). These mean performance improvements are similar to data summarized in Table 1 for running-specific studies (1.5 ± 1.1% and 0.3 ± 1.7%, respectively).
Caffeine has been shown to alter neural function via reducing the inhibitory effects of adenosine (17) and potentially augmenting motor unit recruitment (30,57). An ergogenic effect of caffeine intake on 1,500-m treadmill performance was revealed by Wiles et al. (59) in trained runners. Data revealed that 3 g of caffeinated coffee [containing 2.5 mg·kg−1 BM caffeine as reported by Ganio et al. (18)] improved time trial performance vs. placebo by 4.2 seconds, representing a 1.5% improvement in performance. Other data showed improved sprint cycling performance (41,60) and 2,000-m rowing performance in athletes (9). Although these activities are not running, they were at similar relative intensities and durations to middle-distance running. Clearly, more research is merited to elucidate effects of caffeine on 400- to 1,500-m running performance and potentially examine any combined effect of sodium bicarbonate/citrate and caffeine ingestion on performance.
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%).
Long-distance running (8–10 km to 42.2 km) has a great dependence on oxidative phosphorylation of carbohydrate and fats to provide a constant source of fuel for working muscle. Causes of fatigue can vary for these distances, with mechanisms of fatigue in 8- to 10-km races similar to those of middle-distance running, whereas fatigue in half marathons and marathons is generally because of CHO depletion. Numerous field and laboratory studies indicate that carbohydrate and carbohydrate-electrolyte ingestion during endurance running (15–40 km) can improve running performance by 2–10% (32–34,54). This is likely because of the maintenance of blood glucose, provision of additional carbohydrate for working muscles (54), and maintenance of electrolytes to help sustain muscular contraction through the Na+-K+ pump (31). Fluid ingestion during prolonged exercise is known to attenuate cardiovascular drift and enhance thermoregulation, especially in conditions of high heat stress (20,36). However, carbohydrate gel intake containing 1.1 g·kg−1 of CHO did not affect (−0.3%) half-marathon performance in elite runners (10). Other studies in which performance was improved (48,55,58) or unaltered (49) examined effects of CHO ingestion during prolonged treadmill running but were excluded because they did not meet the inclusion criteria. Recent studies (44,45) showed that exogenous carbohydrate oxidation is similar when liquid, semisolid, and solid CHO sources are ingested during exercise, yet these studies used a low-intensity cycling protocol (∼60% V[Combining Dot Above]O2max), so it is unknown how gels or sports bars would affect performance of higher-intensity exercise. This is particularly important because runners tend to be more prone to GI distress with CHO supplementation than cyclists (8,43). Several studies (48,49) have reported equivocal effects of a CHO-electrolyte solution on a 1-hour performance run. It seems that if runners begin exercise in a fed state (high-CHO meal ∼3 hours pre-exercise), CHO-electrolyte solutions will have minimal effects on performance (49). However, if runners exercise in a fasted (>12 hours) state, ingesting CHO-electrolyte solutions before and during prolonged running provides a clear performance benefit of 2.5% in regard to total distance covered and 2.8% in regard to average speed (48). It is important to note that runners are unlikely to fast before competition, so these data must be interpreted with caution, but this may be an acceptable strategy for training.
Recently, carbohydrate mouth–rinsing solutions have gained interests among researchers. It seems that the mere presence of carbohydrate in the mouth can activate receptors in the brain, potentially improving performance (14). For example, Rollo et al. (47) reported improved performance in a bout of 60-minute duration; however, the subjects in these studies were fasted (>12 hours), and the protocols did not simulate competition. More research on this novel supplement method is needed before recommendations can be made regarding its efficacy for runners.
In trained runners, Bridge and Jones (6) reported improved performance with 5 mg·kg−1 of caffeine (−24 seconds; 1.2%) vs. placebo during an 8-km track race , whereas Bell et al. (4) found a nonsignificant 1.7% improvement in 10-km treadmill performance in subjects wearing 11 kg of military gear with 4 mg·kg−1 of caffeine. Studies have examined the combined effect of CAFF and CHO on performance, with a recent meta-analysis indicating a small but worthwhile improvement of 6% compared with CHO alone (16). However, only 3 of 21 studies examined used running as the mode of exercise (16). Thus, it is unclear if the same performance enhancement typically observed during cycling also occurs with running. As many widely accessible sports gels, chews, and bars contain small doses of caffeine (∼35 to 50 mg per serving), studies are merited to examine the efficacy of various modes of CHO, CAFF, and CAFF + CHO supplementation on performance in both field and laboratory settings compared with placebo.
Challenges and Recommendations for Future Research
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).
Overall, sodium bicarbonate at doses equal to 0.3 g·kg−1 BM ingested with a high-carbohydrate meal ∼2 hours pre-exercise likely improves middle-distance running performance. Ingestion of >3 mg·kg−1 BM of caffeine consumed 1 hour pre-exercise may improve middle-distance running performance. Sodium citrate at doses of 0.5 g·kg−1 BM ingested 1.5–2 hours pre-exercise may also benefit middle-distance running, albeit with small increases in body mass after ingestion. It is important to note that the performance improvement observed with caffeine and bicarbonate is small (1.1 and 1.5%) but meaningful to the athlete. For example, sodium bicarbonate improves performance in a competitive (4 min·240 s−1) 1,500-m runner by 3.6 seconds, whereas caffeine improves 5-km performance in a competitive (15 min·900 s−1) runner by ∼10 seconds. However, performance benefits of citrate are unclear at present. Carbohydrates should be ingested before and during long-distance running to improve performance. For example, ≤30 g·h−1 of CHO (equivalent to 16 oz of Gatorade or Powerade) should be ingested for events 1–2 hours in duration; ≤60 g·h−1 for events 2–3 hours in duration; and ≤90 g·h−1 for events >3 hours (27).
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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