The research was published in the International Journal of Exercise Science. It was the work of researchers associated with Purdue University, Northern Illinois University and Boise State University.
Despite ubiquity of caffeine, still some disagreement about precise effects
Caffeine is one of the mostly widely used dietary ingredients in the world. The study quoted statistics that show that 85% of the population in the United States consumes at least one caffeinated beverage a day. The 90th percentile for caffeine intake is 380 mg/day for all age groups combined. The most popular supplements for young people include caffeinated energy drinks and caffeine-containing pills.
High intensity interval training (HIIT) has become a popular form of exercise, especially among younger people. Repeated sprint ability (RSA) is one form of this and formed the primary outcome of the new research.
The authors noted that caffeine supplementation has been mostly widely studied in relation to endurance exercise and it is in this realm that it has shown the most consistent results. The results in HIIT, and in particular RSA, are fewer and farther between, and generally have returned equivocal results, with some studies showing a benefit with others finding none.
Further, the researchers noted that many of these studies were done in trained athletes and used relative (i.e., keyed to body weight) dosages of caffeine. But that doesn’t match the real world, they said, in which caffeine users get whatever dosage is presented in the products they use.
Studying caffeine in the real world
To study whether caffeine had an effect under more ‘real world’ conditions, the authors recruited a cohort of 35 young people attending Northern Illinois University, of whom 32 completed the study. They ranged from 218 to 30 years of age, and the cohort was about evenly split between men and women. All were at a healthy weight without complicating conditions and none were trained athletes.
The study was structured to test a single 200 mg dose of caffeine against placebo. The primary outcome was the running times over a 30 meter sprint repeated six times with 20 seconds in between. The researchers also tested blood lactate (BLa) levels and had the subjects respond to questions about the perceived rate of exertion (PRE).
The researchers found that the caffeine intervention had a statistically significant effect on the sprint times. The caffeine group had a higher BLa measurement, too, which was indicative of the greater work they performed compared to the placebo group. However, increasing BLa can be a self limiting factor, due to a greater feeling of discomfort. Yet the caffeine group showed no increase in RPE, which otherwise would be expected.
In conclusion, the authors noted: “This investigation provides evidence that supplementing 200 mg of caffeine prior to exercise enhances RSA, determined by decreased total ST, in young, healthy non-athletes. This may be attributed to caffeine’s ability to blunt elevations in perceived exertion despite increased exercise intensity measured by BLa concentrations.”
Source: International Journal of Exercise Science
The Effects of Acute Caffeine Supplementation on Repeated-Sprint Ability in Healthy Young Non-Athletes
Authors: Belbis MD, et al.