Browsing Google scholar, trying to select the perfect article for this inaugural post, I became quickly overwhelmed by the wealth of research not being communicated to the running community. If I wasn’t also happily consumed with studying brains and memory (and if dropping out of grad school were an option), I would gladly devote myself to sharing each of these valuable findings with you, dear reader. All in good time. As this blog is in its infancy and has yet to develop a focused direction or personality, it seems most appropriate to begin broadly.
As such, I’d like to share Heneghan et al.’s recent review ¹ of the evidence for claims that sports drinks can serve as performance enhancers. Reading just the title of the chosen article, “Forty years of sports performance research and little insight gained,” underscores a major problem in sports science – namely, that despite some good intentions and a spattering of important breakthroughs, unacceptably low standards are slowing the rate of actual progress. In this study, the authors requested study references from a number of sports drink manufacturers in order to systematically review the existing scientific support for their products. Yet disturbingly, only one (Glaxo-Smith) complied. The authors thus reviewed 105 studies on the drink Lucozade published since 1971 and report several concerning findings, primarily related to statistical analyses or experimental design.
Most of the studies, which frequently compared effects of consuming a sports drink versus a placebo control, used very small sample sizes (median number of participants per study = 9). As a general rule, without sufficient data you cannot trust that your findings are reliable, rather than an artifact of the variability in your particular sample. Given these small sample sizes, it’s not surprising that few studies performed the requisite power calculations, which determine before conducting the study how many subjects would be needed to detect the desired effect. Granted, as this is one step that scientists from many fields like to shove under a rug and reserve mostly for grant-writing propaganda, sports drink researchers should not be the only ones under attack for this statistical crime. Even if we overlook the weak statistical power, some of the studies appear guilty of “data dredging”, or cherry-picking analyses to yield the best results, a major statistical no-no! A particularly worrisome example is this study ² that examined differences in endurance running capacity after a carbohydrate-rich or non-carbohydrate drink. They excluded the initial 75 minutes of testing during the running capacity test, which inflated a 3% performance enhancement to a whopping 33% for the treatment group compared to the control group.
Poor study design
Beyond questions of statistical rigor, the primary outcome variables – those critical criteria upon which researchers base their conclusions – were often poorly chosen. For example, some did not even evaluate how the drinks influenced performance. Of those that did, one ³ didn’t distinguish between elite and non-elite athletes and others used unreliable measures, possibly introducing major confounds. Still others used seemingly random physiological variables that are associated with complex biological responses and thus correlate weakly with any meaningful performance measures. Even worse, since most studies were not properly blinded, it’s plausible that participants’ or researchers’ awareness that they were taking the carbohydrate drink or placebo substantially biased their outcome.
The reviewers touch on redeeming qualities in just handful of studies that succeed at reporting legitimate, insightful results. These infrequent gems include findings that responses to sports drinks depend on environmental factors such as temperature 4,5, and vary according to dose, such that a moderate carbohydrate concentration is more effective than highly dilute 6 or saturated drinks 7. Even without knowledge of these “stand-out” studies, I suspect most athletes could tell you they get more kick from their sports drink if it’s not completely watered down, or if they’re dehydrated from excessive heat.
A bottom line?
So after reviewing over a hundred rigorously (ehem) conducted studies, what do the authors conclude?
“… carbohydrate ingestion can improve exercise performance, but consuming large amounts is not a good strategy … people should develop their own strategies for carbohydrate intake largely by trial and error.”
Clearly this makes an alarming statement about the standards being applied to sports drink research, in that the bottom line derived from this wealth of evidence is to “figure it out yourself”. More importantly, runner, how does this help you, as you approach the mile 18 aid station of your next marathon and must decide whether or not to reach for that cup of blue sugar-water? If it makes you run faster, stronger or longer, grab that cup. If not, don’t necessarily believe everything you hear, even if they call it science. Indeed, did we really need forty years of research to reach that conclusion?
Incidentally, right after posting this I discovered a fantastic new paper (Smith JW et al. 2012. Med Sci Sports Exerc) that deserves mention. The study tested a group of cyclists and triathletes as they completed a 2-hour constant cycling ride followed by a 20-km timed trial. Cyclists completed twelve sessions during which they consumed one of eleven concentrations of carbohydrate drink, or placebo. What did they find? A curvilinear dose-response curve, meaning that with increasing carbohydrate concentration, performance improved up to a certain point (78 g/hr) and then began to decline. As you know from the above discussion, this isn’t particularly surprising. But there a several features of this study that instill much greater confidence in their finding. First, they tested a respectable sample size of 51 athletes, across three sites, minimizing the chances of sampling bias. Second, they examined a full spectrum of doses to more precisely pinpoint the optimal concentration and kept other factors well controlled. Lastly, the experiments were double-blinded, meaning that both the cyclists and experimenters didn’t know what they were drinking – this is good! Props to Smith and colleagues for a great study … now, let others follow suit.
- Heneghan C et al. 2012. Forty years of sports performance research and little insight gained. BMJ 345:e4797.
- Nicholas CW et al. 1995. Influence of ingesting a carbohydrate-electrolyte solution on endurance capacity during intermittent, high-intensity shuttle running. J Sports Sci 13:283-90.
- Ali A et al. 2007. The Influence of Carbohydrate-Electrolyte Ingestion on Soccer Skill Performance. Med Sci Sports Exerc 39(:1969-76.
- Morris JG et al. 2003. The influence of a 6.5% carbohydrate-electrolyte solution on performance of prolonged intermittent high-intensity running at 30 degrees C. J Sports Sci 21:371-81.
- Galloway SD et al. 2001. Exogenous carbohydrate oxidation from drinks ingested during prolonged exercise in a cold environment in humans. J Appl Physiol 91:654-60.
- Vist GE & Maughan RJ. 1994. Gastric emptying of ingested solutions in man: effect of beverage glucose concentration. Med Sci Sports Exerc 26(10):1269-73.
- Tsintzas OK et al. 1995. Influence of carbohydrate-electrolyte drinks on marathon running performance. Eur J Appl Physiol Occup Physiol 70:154-60.
Heneghan, C., Perera, R., Nunan, D., Mahtani, K., & Gill, P. (2012). Forty years of sports performance research and little insight gained BMJ, 345 (jul18 3) DOI: 10.1136/bmj.e4797