Caffeine may enhance performance in athletes, but not in couch potatoes

BUFFALO, N. Y. – A preliminary study conducted at the University at Buffalo has found that although trained athletes derive performance benefits from caffeine, most sedentary or lightly active adults do not like exercise more – or perceive their exertion to be less – when given caffeine.

What caffeine does do, according to the study, is make them exercise for longer periods, which could increase their likelihood of achieving the American College of Sports Medicine recommendations for physical activity.

The study, “Acute and chronic caffeine administration increases physical activity in sedentary adults,” was posted online in Nutrition Research on May 10.

Its authors are Patrick Schrader and Leah M. Panek, graduate students in the UB of Department of Exercise and Nutrition Sciences, UB School of Public Health and Health Professions, and Jennifer Temple, PhD, professor, Department of Exercise and Nutrition Sciences.

“What is important about this study,” says Temple, “is that it indicates that the ergogenic (performance-enhancing) properties of caffeine are quite different for trained athletes than for sedentary adults.”

Previous studies with athletes have found that caffeine enhances their performance and reduces their scores on the rated perceived exertion scale or RPE. The UB researchers hypothesized that caffeine ingestion would have the same effect on sedentary adults, that is, it would increase their capacity for physical exertion by eliminating fatigue symptoms and reducing their perception of exertion while exercising.

The researchers found, however, that:

• Caffeine did little to modify the subjects’ capacity for physical exertion or their ratings of how much exertion they had expended during periods of exercise. 
• Time, however, had an important influence. As time went on, subjects engaging in exercise said they liked physical activity more and more, regardless of their caffeine-ingestion status, and it lowered their ratings on the RPE scale.
• Women who had been treated with caffeine showed a particular increase in their “liking” of exercise, while women treated with placebo and male subjects treated with either caffeine or placebo, did not. 
• During the eighth or last study session (as compared with session one) most participants increased the time they spent in self-determined exercise, but this effect was significantly greater in participants who were given caffeine immediately before they exercised in this session, regardless of their caffeine treatment during the rest of the study.

The study involved 35 subjects between the ages of 18 and 50, half men and half women, who attended eight laboratory sessions, 60 to 75 minutes in length, over the course of two weeks. All were asked to abstain from caffeine for 24 hours before each session and asked to refrain from engaging in physical activities on the day of their visits.

At each session, half the participants were given caffeine (3 mg/kg) and half a placebo in a sports drink. At the sessions, participants completed treadmill walking at 60 percent to 70 percent of their maximal heart rate at baseline and for six of the seven subsequent visits. To investigate the potential synergistic effects of acute and chronic caffeine on self-determined exercise duration, participants were re-randomized to either the same or different condition for the last (or eighth) visit, creating four chronic/acute treatment groups (placebo/placebo, placebo/caffeine, caffeine/placebo, caffeine/caffeine). That is, they received placebo all along, then caffeine at the last session; placebo all along and placebo at the last session, etc.

At each visit, participants rated how much they liked the activity and how much exertion they thought they had expended. The length of their self-determined exercise sessions was also recorded and analyzed.

The researchers say their future efforts will focus on whether there are dose-dependent effects of caffeine on exercise liking and RPE in sedentary adults, and whether a longer training period might have been necessary to see significant effects of caffeine on liking of exercise and RPE.

“Once we have good data on the most effective dose of caffeine and period of caffeine/exercise pairing,” says Temple, “we hope to determine if caffeine paired with exercise can be used outside the laboratory to make sedentary individuals more likely to be physically active.”