Matt Poe discusses the safety and effectiveness, if any, by using caffeine as a stimulant.

An Objective Discussion on the Use Of Caffeine

By Matt Poe, MS

Matt Poe > Let’s pose two questions for this discussion!

PART 1: is there any neural benefit (improved alertness, improved neuromuscular recruitment, etc) for an individual to ingest moderate amounts of caffeine prior to and/or during their activities? (consider moderate to be 300 mg or less)

In a study that assessed recreationally active individuals participating aerobic-dance bench stepping, it was determined that neither 3mg/kg of body weight or 6 mg/kg of body weight had any effect on HR, VO2, VCO2, minute ventilation, RER, RPE, or REE. (1)  The effects of caffeine intake combined with casual exercise for fitness and weight management showed an increase in energy expenditure (REE) with moderate amounts being ingested. (2)

Another study examined the physiological effects of caffeine on healthy subjects participating in maximal cycling bouts.  It was also determined that caffeine had no significant effect on HR, RPE, peak power, and work output.  In the same study it was suggested that not only does caffeine show no real ergogenic benefits but may even be detrimental to anaerobic performance. (3)  The study cited a slower time to reach peak power in a second exercise bout following a rest period after the first bout.

Increased testosterone along with a concurrent increase in cortisol was observed in professional rugby players. (4) The anabolic effects of the increased bioavailabilty of testosterone may be negated by the increase in cortisol levels as well.

PART 2: for the healthy non athlete are there any risk factors for consuming moderate levels of caffeine daily (moderate = 300 mg per day or less).

Much of the research suggests that little to no side effects or risk factors that should be considered regarding ingestion of caffeine and the effects of exercise.  There is research that warns against potential side effects such as significantly higher blood lactate and significantly slower time to peak power.  In the same study one subject experienced hand tremors, feelings of hyperactivity and restlessness.  Another experienced restlessness, agitation, dizziness, and nausea. (3) 

No ill effects on the body fluid balance were observed with moderate ingestion of caffeine after exercise heat exposure. (5) Some other potential side effects observed were gastric upset, withdrawal, sleep disturbance, and possible interactions with other dietary supplements. (6)

Caffeine intake has been shown to promote calcium loss, thus increasing the risk for osteoporosis.  This can be most problematic in those who replace nutrient rich beverages like juice and milk with caffeinated beverages. (6)  Caffeine intake has also been shown to reduce fertility in women.  Active females often have menstrual dysfunction which may be exacerbated by high caffeine intake. In the same article it was suggested that caffeine interferes with insulin action which may affect those with poor insulin sensitivity, diabetics, or the recreational athlete. (7)

Modest amount of caffeine appear to have no significant effect on heart rate variability(HRV) in young, healthy subjects. (8)  This is significant because HRV has become an important risk factor in cardiovascular events (MI, CVA, etc).

References

1.      Ahrens JN, Lloyd LK, Crixell SH, and Walker JL. The effects of caffeine in women during aerobic-dance bench stepping. Int J Sport Nutr Exer Metab. 17:27-34, 2007.

2.      Ahrens JN, Crixell SH, Lloyd LK, and Walker JL.  The physiological effects of caffeine in women during treadmill walking. J Strength Cond Res. 21:164-168, 2007.

3.      Crowe MJ, Leicht AS, and Spinks WL. Physiological and cognitive responses to caffeine during repeated, high intensity exercise. Int J Sport Nutr Exer Metab. 16:528-544, 2006.

4.      Beaven CM, Hopkins WG, Hansen KT, Wood MR, Cronin JB, and Lowe TE. Dose effect of caffeine on testosterone and cortisol responses to resistance exercise. Int J Sport Nutr Exer Metab. 18:131-141, 2008.

5.      Dias JC, Roti MW, Pumerantz AC, Watson G, Judelson DA, Casa DJ, and Armstrong LE. Rehydration after exercise dehydration in heat: effects of caffeine intake. J Sport Rehabil. 14:294-300, 2005.

6.      Tunnicliffe JM, Erdman KA, Reimer RA, Lun V, and Shearer J. Consumption of dietary caffeine and coffee in physically active populations:physiological interactions. Appl Physiol Nutr Metab. 33:1301-1310, 2008.

7.      Graham TE. Caffeine, coffee, and ephedrine: impact on exercise performance and metabolism. Can J Appl Physiol. 26:S103-S119, 2001.

8.      Rauh R, Burkert M, Siepmann M, and Mueck-Weymann M. Acute effects of caffeine on heart rate variability in habitual caffeine consumers. Clin Physiol Funct Imaging. 26:163-166, 2006.