The Caffeine Boost – Ergogenic Effects of Caffeine

Diet | Exercise | Fitness | Lifestyle | Nutrition

Posted on July 10, 2015 by Jenny Cromack

Caffeine Boost: Fact or Fiction?

For decades the discussion around the ergogenic effects of caffeine (performance enhancing) have been back and forth. The actual effects of caffeine on the body and exercise performance are still in limbo and the arguments continue.

The Effects of Caffeine

Several theories exist for the mechanism by which caffeine may enhance performance. One of these theories is that caffeine has a direct effect on the central nervous system and the signals between the brain and the muscles. Caffeine may stimulate the release of hormones and neurochemicals that help reduce the sense of effort, hence the reported lower ratings of perceived exertion (RPE) when caffeine is used. This means that people don’t feel like they are working as hard as they are, so the exercise feels easier for them. This may mean that caffeine actually has a huge effect on the CNS as suggested, and if people believe the exercise is easier they may work harder.

Evidence also shows that consuming 3 coffees throughout a day appeared to increase serotonin (happiness hormone) levels and therefore may lift our mood and make us feel more positive and therefore likely to adhere to healthier life choices.

A second theory suggests that caffeine has a direct effect on skeletal muscle and causes an influx of ions and increases the sensitivity of the muscle. This causes the muscle fibres to become more excitable and therefore increases muscle fibre recruitment and muscle contraction which may help with exercise performance.

A third proposal is that caffeine increases the circulation of adrenaline which stimulates increased fat breakdown and release into the bloodstream. As well as this it is suggested that caffeine interferes with specific receptors in the body that usually inhibit fat mobilisation. This all means that if fat mobilisation is increased then carbohydrate can be spared as an energy source. Some studies have found that caffeine does appear to increase the VO2 during exercise trials. This would suggest that aerobic metabolism is increased and higher intensities of work are more easily sustained with caffeine (Cureton et al., 2007; Jenkins et al., 2008).

The ingestion of caffeine does appear to increase the time to exhaustion and improved endurance capacity in some cases. There are several reports of improvements in both running and cycling trials, these improvements are represented through the increased time to exhaustion but also the total amount of work done (Cureton et al., 2007; Jenkins et al., 2008; Sasaki et al., 1987). This is linked to the increase in fat metabolism and the sparring of carbohydrate as a fuel source. Another potential mechanism is the increased excitability of muscle fibres allowing more work to be done.

As well as increased fat metabolism caffeine may suppress glucose-related enzyme function and insulin release resulting in less spikes in insulin activity and thus the storage of body fat. These mechanisms may not only benefit performance but may also help with any body shape goals such as body fat reduction.

The above suggests that caffeine may be a potentially effective substance for helping improve performance, and reducing the perceived effort during endurance based activities such as running or cycling, as well as for achieving body related health and fitness goals.

However, as with all arguments there is always two sides to the story and many studies fail to find any significant effect of caffeine on performance. An experiment with soldiers in a walking test to exhaustion found no effect of caffeine (Falk et al., 1990). Similarly, there was no significant effect of caffeine on running performance in a group of male and females subjects (Butts & Crowell, 1985).

The majority of studies also show no effect of caffeine on short-intense bouts of exercise such as sprint performance (Collomp et al., 1991; Williams et al., 1988). One study actually found that caffeine actually resulted in a drop in power output during short burst cycling tests (Greer et al., 1998). There is still uncertainty surrounding caffeine and high intensity exercise but without further investigation it would seem that caffeine is not an ideal source of performance enhancement for these types of short-intense bouts of activity.

Some studies do have flaws in that some failed to control the caffeine intake of the supposed placebo or non-caffeine group therefore skewing the lack of significant findings. This balance of for and against arguments makes it hard to make a conclusion on caffeine so understanding the metabolic effects may help you make up your own mind on the use of caffeine. Some of the reason for conflicting findings may be that varying doses of caffeine have been explored, the effect may also vary with fitness levels, habitual caffeine consumption, and the type and duration of exercise.

Things to Consider

Some evidence suggests that caffeine actually prevents our levels of cortisol from dropping. Cortisol is our “stress hormone” and can lead to hunger, and slowing of the metabolism, which goes completely against the above. Cortisol also has been linked to excessive storage of fat around the abdominal region. Therefore excessive caffeine intake should be avoided and possibly timed around less stressful times of the day. This also means that if you are looking for a boost for your training but your goals are related to shedding that body fat this evidence suggests that large volumes of caffeine may not be a wise choice.

So What Should You Do?

It is very hard to swing one way or another in the argument for caffeine as it has been linked to several performance benefits and a lift in mood, but also a few performance deficits or no effects at all. Its proposed mechanisms offer potential benefit to metabolism and fat breakdown which would be good for prolonging exercise and also helping reduce body fat levels. On the flip side it also has its link to elevated cortisol levels and thus may jeopardise some body fat reduction.

You are probably sat thinking great I still don’t know what to do. My advice would be that if you are already a heavy coffee drinker having it before exercises for the “boost” is probably not going to make any difference. Also if you have specific body fat goals and already lead a stressful life the links between caffeine and “stress hormones” may suggest that it may not be the best route for you to take. After all would you want to sacrifice any body fat goals for the sake of running a little longer?

However, if you are someone looking for that well needed boost and aren’t already a huge coffee drinker, or have major concerns with specific body fat goals then I don’t see any reason not to try it, see if it works, if not then you haven’t lost out on anything. It may be the difference between you and personal best or it may just make you feel a little happier and find the workout that little bit easier.


Butts, N.K., and D. Crowell (1985). Effect of caffeine ingestion on cardjorespiratory endurance in men and women. Research Quarterly. 56, 301-305.

Collomp, K., S. Ahmaidi, M. Audran, J.-L. Chanal, and C. Prefaut. (1991). Effects of caffeine ingestion on performance and anaerobic metabolism during the Wingate test. International Journal of Sports Medicine, 12, 439- 443.

Cureton, K. J., Warren, G. L., Millard-Stafford, M. L., Wingo, J. E., Trilk, J., & Buyckx, M. (2007). Caffeinated sports drink: ergogenic effects and possible mechanisms. International journal of sport nutrition and exercise metabolism,17(1), 35.

Falk, B., R. Burstein, J. Rosenblum, Y. Shapiro, E. Zylber-Katz, and N. Bashan. (1990). Effects of caffeine ingestion on body fluid balance and thermoregulation during exercise. Canadian Journal of Physiology and Pharmacolology. 68, 889-892.

Jenkins, N. T., Trilk, J. L., Singhal, A., O’Connor, P. J., & Cureton, K. J. (2008). Ergogenic effects of low doses of caffeine on cycling performance.International journal of sport nutrition and exercise metabolism, 18(3), 328.

Sasaki, H., J. Maeda, S. Usui, and T. Ishiko. (1987). Effect of caffeine ingestion on performance of prolonged strenuous running. International Journal of Sports Medicine, 8, 261-265.

Williams, J.H., J.F. Signorile, W.S. Barnes, and T.W. Henrich. (1988). Caffeine, maximal power output and fatigue. British Journal of Sports Medicine, 229, 132- 134.