Young Ju, Ph.D.

You have probably heard of one or more of the following: Monster Energy, Red Bull, Alani Nu, Celsius, Rockstar Energy, Bang Energy, and Ghost. These energy drinks are widely consumed to enhance energy, alertness, and physical performance. Let’s look at what’s in them and how they could affect tennis performance and training.

Energy Drinks

Energy drinks are defined by the CDC (1) as beverages that contain:

• high amounts of caffeine

• added sugars (8-11%)

• other additives and natural stimulants (including vitamins, minerals, taurine, amino acids, and mixtures of herbal substances)

Energy drinks are considered dietary supplements and thus are not required to have FDA pre-market approval. The FDA does not regulate the amounts of caffeine and other stimulants in energy drinks. These products claim to enhance physical stamina, focus, cognition, alertness, and wakefulness. Since their first appearance in 1960 in Europe and Asia, consumption has rapidly increased worldwide. In the US, energy drinks are the second-most-consumed dietary supplement (>1.5 billion units in 2022) - right after multivitamins. Consumption of energy drinks is most prevalent in men (18-34 years), but about one-third of teens (12-17 years) use these products regularly (2).

Key Ingredients in Energy Drinks

It is believed that any effects of energy drinks on sports performance are mainly due to caffeine and taurine.

The primary ingredient in energy drinks is caffeine (50-200 mg in 8-12 oz.). Caffeine is the most widely consumed psychoactive substance worldwide. Approximately 90% of adults consume caffeine regularly from dietary sources (~200 mg/day).

Taurine is another common ingredient in energy drinks (35-1,500 mg in 8 oz.). It is an amino acid and stimulant found in muscles. Combining caffeine with taurine could enhance muscle function. Meat and seafood are good food sources of taurine.

Guarana is an additional source of caffeine. Guarana seeds may contain 4-6 times more caffeine than coffee beans.

L-carnitine is an amino acid that is involved in breaking down fats as an alternative energy source. However, its role in energy drinks is controversial.

Note that many bottles and cans of energy drinks contain multiple servings.

Caffeine and Exercise

Many studies have examined the effect of caffeine on exercise performance, and a growing number have tested various caffeine sources including coffee, energy drinks, herbal formulas, and pre-workout supplements (containing 150-300 mg of caffeine) (3). 

With regard to physical exercise, energy drinks are used for various purposes including pre-training, nutritional supplementation, and pharmacological or psychological approaches to improve training and exercise outcomes. Several recent reviews evaluated the effects of caffeine and energy drinks on sports performance including racket sports (3, 4, 5).

Research studies done with tennis players showed that 3-6 mg of caffeine per kg body weight (~210-420 mg/154 pounds) taken 30-60 min before a match was effective in enhancing performance. Studies concluded that in tennis players at any level (ages 15-51 years), energy drinks improved power skills (stroke, serve, grip force, and sprints) and mental aspects (accuracy and successful shots). But energy drinks did not change how hard a player feels the body is working (physical activity intensity level). Lower doses of caffeine (0.2-0.25 mg/kg body weight) did not affect performance.

Caffeine Content in Various Products

Caffeine content in energy drinks differs from other traditional caffeine-containing beverages, such as coffee, tea, soft drinks, or sports drinks: 

• Caffeine gums, chews, bars and tablets usually contain 100-200 mg of caffeine per serving. These products may deliver caffeine faster than energy drinks.

• Soft drinks typically contain 35-40 mg of caffeine in 12 oz.

• Coffee contains 85-100 mg caffeine in 8 oz. (~4 mg in decaffeinated coffee)

• Tea contains 25-50 mg caffeine in 8 oz.

• Chocolate contains 4-12 mg of caffeine per serving size.

Energy shots contain the same ingredients as energy drinks, but in a concentrated form (220 mg in 2 oz. or less). These products use the same claim as energy drinks.

Sports drinks differ from energy drinks and contain electrolytes (sodium, potassium, magnesium, and calcium, etc.) along with sugar (6-8%) or low- or no-calorie sweeteners. These products are designed to hydrate the body before, during, or after exercise. (These products typically do not contain caffeine unless so labeled.)

Safety Concerns (1, 2, 6)

Individuals vary greatly in how caffeine absorption, metabolism, utilization, and excretion affect health and performance. Because they contain caffeine as well as sugar and other ingredients, energy drinks can have side effects:

• Caffeine intake can adversely affect mood and sleep quality.

• Caffeine intake in athletes with performance anxiety may aggravate their conditions.

• Caffeine intake may cause serious heart and blood vessel problems such as irregular heart rhythm and increased heart rate and blood pressure.

• Caffeine intake may have diuretic effects causing dehydration. Energy drinks should not be used for hydration before, during, or after exercise.

• Health claims about some ingredients found in energy drinks are not well studied.

• Energy drinks contain high amounts of added sugar that could increase blood glucose.

Overall

Energy drinks (up to 2 servings per day, i.e., caffeine up to 400 mg) may reduce muscle fatigue and pain, enhance muscle mobility, improve endurance, and boost mental and physical performance. However, these products also contain high amounts of sugar, vitamins, herbs, and stimulants that may not be necessary for the average person, and that could negatively affect people with heart disease and diabetes. Also, energy drinks should never be considered as substitutes for a healthy diet or for hydration purposes.

The bottom line is that energy drinks may not make you a tennis RockStar, but the recommended amount of caffeine 30 to 60 minutes before your match may provide performance benefits for you. You should be aware of potential side effects, and as always, read any Supplement Facts and Nutrition Facts labels carefully.

References

1.      Center for Disease Control and Prevention. Energy Drinks. https://www.cdc.gov/healthyschools/nutrition/energy.htm#:~:text=What%20Is%20an%20Energy%20Drink,%2C%20heart%20rate%2C%20and%20breathing.

2.      National Center for Complementary and Integrative Health. Energy Drinks. https://www.nccih.nih.gov/health/energy-drinks

3.      Guest, N.S., VanDusseldorp, T.A., Nelson, M.T., Grgic, J., Schoenfeld, B.J., Jenkins, N.D., Arent, S.M., Antonio, J., Stout, J.R., Trexler, E.T., Smith-Ryan, A.E., Goldstein, E.R. Ka;man, E.S., Campbell, B. I. International society of sports nutrition position stand: caffeine and exercise performance. J Int Soc Sports Nutr 2021, 18:1.

4.      Vicente-Salar, N., Santos-Sanchez, G., Roche, E. Nutritional ergogenic acids in racquet sports: A Systematic Review. Nutrients 2020, 12:2842.

5.      Gutierrez-Hellin, J., Varillas-Delgado, D. Energy drinks and sports performance, cardiovascular risk, and genetic associations; Future prospects. Nutrients 2021, 13(3):715.

6.      Kaur, A., Yousuf, H., Ramgobin-Marshall, D., Jain, R. Energy drink consumption: a rising public health issue. Rev. Cardiovasc. Med. 2022, 23(3):83.    

People with any health problems should talk to their healthcare providers about energy drink intake. This information is provided for your reference and you use at your own risk; you should rely on your medical professional for medical advice.