Critique of an Article from the Journal of Applied Physiology

Critique of an article from the Journal of Applied Physiology

"Effect of different protocols of caffeine intake on metabolism and endurance performance"

By Steve Bradley, BUSN 670, Queens University

February 3rd, 2004

Introduction

In 2002, a group of Australian researchers published a paper entitled the "Effect of different protocols of caffeine intake on metabolism and endurance performance". Caffeine use during sporting events has become much more popular and has widely studied. The purpose of the research was to examine the work increasing (ergogenic) effects of differing regiments of caffeine on metabolism and performance while simulating the typical nutritional preparation an athlete would do for a race. The study also sought to examine the effect of timing of caffeine intake, comparing results when caffeine was given before an event (precaf) to results from caffeine given during an event (durcaf). In addition, the researchers wanted to understand the practice of endurance athletes drinking defizzed Coca-Cola towards the end of a race. It was widely observed that many triathletes and marathoners feel they derive a boost from consuming Coca-Cola in the final stages of an event as a replacement to sports drinks.

Participants and Overall Research Design

Two similar, but separate studies were conducted. The first study (A) used 12 highly trained athletes, either triathletes or cyclists. The second study (B) used a smaller sample of 8 athletes with similar backgrounds. While training histories were similar, caffeine intake histories varied from occasional to regular intake of up to ~150 mg/day (2mg/Kg). Subjects first performed a maximal incremental power test to determine their VO2 peak, a measurement of the body's ability to taken in O2 and turn it into work. A work rate of 70% of VO2 peak was used for the rest of the trials. This compensated for varying levels of fitness among the athletes and corresponds to mid range workout. The subjects refrained from caffeine, standardized diet, and standardized training for 48 hrs before the trials. For 24 hours before the trials, each subject was given a prepackaged standard diet. Exercise and food diaries were kept and checked for compliance.

Each trial consisted of two hours of steady state cycling at 70% VO2 peak immediately followed by an all out time trial. Study A compared placebo (no caffeine), caffeine before the trial (precaf), during trial (durcaf), and cola as a replacement for a 6% CHO (carbohydrate/sugar) sports drink just before the final time trial. Study B was similar to study A, but moved up the cola drink intake to allow the athletes to consume the cola at a rate that simulated race conditions. Study B also compared decaffeinated 6% CHO cola (control), caffeinated 6% CHO cola (Caf), decaffeinated 11% CHO cola (extraCHO), and caffeinated 11% CHO (Coke). This allowed determination of whether effects were from caffeine, increased sugar content, or some combination.

Results and Discussion

The metabolism results of study A showed caffeine results (Fig. A) as expected. Pre-caf gave the earliest caffeine reading, followed by dur-caf. Urinary caffeine levels (Fig. B) were well below the International Olympic Committee regulation of 12µg/ml. Plasma analysis showed that blood glucose levels were higher in the pre-caf treatment, possibly due an increase in metabolic rate from the caffeine. Blood glucose levels were lowest for the placebo treatment both during and at the end of the time trial.

Respiration data showed an increase in the amount of air consumed for the both the pre-caf and dur-caf trials, with the pre-caf increase starting almost immediately. Rates of perceived exertion were recorded during the trials. As expected, the subject's ratings indicated that the placebo trial required the most effort, while the pre-caf trial required the least effort. Results of the time trials (Table 1) show about a 3% enhancement in performance for each treatment when compared with the placebo. While this was expected in the caffeine trials (pre-caf and dur-caf), it was not expected in the Coke treatment