Caffeine’s Potential Hazard on Exercise Performance

by Scott Kolasinski

For years many people use caffeine to boost their workouts, as well as to burn fat. Supplement companies – including reputable ones – proudly advertise that their products include caffeine. But a recent study shows that using caffeine before your workout could be a bad idea. How can this be so? Let’s look into this apparent contradiction.

A study investigating the cardiovascular safety of caffeine was published last January in the Journal of the American College of Cardiology that showed ingesting caffeine decreased blood flow to the heart during aerobic exercise compared to those who did not consume caffeine. Blood flow to the heart must increase during exercise in order to match the increased need of oxygen.

While ten subjects rode a recumbent bicycle, this study used positron emission tomography, or PET scan, with radioactive-oxygen to measure heart blood flow at rest and immediately after they rode exercise protocol. After the initial protocol was completed, they were given 200 mg of caffeine, approximately 2 cups of coffee, in a tablet, and the exercise test was repeated 50 minutes later.

This same exercise protocol was followed in a second group (8 subjects) who exercised in a chamber simulating the air at about 15,000 feet altitude.
The caffeine dose did not affect blood flow within the heart muscle while the participants were at rest. However, the blood flow measurements taken immediately after exercise were significantly lower when the participants had taken caffeine tablets.

The ratio of exercise blood flow to resting blood flow, called the myocardial flow reserve (MFR), was 22 percent lower in the group at normal air pressure after ingesting caffeine. The MFR was 39 percent lower in the high altitude group.

The decrease in MFR may be because caffeine may block certain receptors in the walls of blood vessels, interfering with adenosine receptors. Adenosine normally causes coronary blood vessels to dilate in response to exercise. However, if a large amount of caffeine is present inhibiting the adenosine receptors to cause the blood vessels to dilate, the MFR decreases and less oxygen gets to the heart.

Because of these results and even considering the small subject size, the researchers were very confident that caffeine prior to exercise would not improve cardiovascular performance and they would not recommend caffeine prior to any sports.

This study would appear to be in stark contrast to a number of sports supplements marketed today as “pre-workout” supplements. Many of these contain at least 200 mg of caffeine and are purported to “enhance performance.” Do these statements make these companies false advertisers?

Maybe, but not necessarily. There is some confusing research out there.

Caffeine has been shown to improve carbohydrate availability in cyclists when mixed in a carbohydrate-containing sports drink (amount of caffeine unknown).

It has been shown to improve stamina. This study found improvements in stamina with the small amount of caffeine in a diet soda, and they also used one cup of coffee, which is half of the dose of the “caffeine blunts blood flow” study. This same study suggested that an improvement in stamina may improve weight loss as well.

Other studies have found that caffeine taken during exercise can delay the onset of fatigue by up to 60 percent.

I heard a lecturer recommend 5 mg caffeine/kg (bodyweight in lbs./2.2 lbs. = kg) bodyweight for endurance events. For anybody over 140 lbs, it becomes a very large recommended amount of caffeine to handle per day – more than the RDA’s recommendation of 300 mg per day.

However, if caffeine really has any sort of “benefits” then why was it removed from the World Anti Doping Agency's (WADA) list of banned substances in January 2004? This suggests that a definitive link between caffeine use and performance enhancement has not yet been established by the research. Various famous athletes have been reported to use caffeine for what they believe is performance enhancement. Hmm....???

Lets try clearing some of the confusion. Caffeine has been shown to be an effective cerebral stimulant, making us feel more awake, alert and focused, which may let us believe that we are performing better, but this is only subjective. The reality is, when exercise demands are at a high intensity, certain amounts of caffeine should be avoided.

It is practical: During a moderate to high-intensity workout, your heart rate is going to increase. If you do a high-volume Crossfit workout, you do not want to have a feeling of suffocation or chest pain because of caffeine and a decreased MRF. It would not make sense to take a large coffee's worth of caffeine prior to your workout.

This is contrary to the recommendations of a number of weight loss supplements on the market and in the fitness magazines, such as Hydroxycut Hardcore, Xenadrine Hardcore, Nutrex Lipo 6, etc. These types of products usually recommend that you take their product prior to exercise in order to have more energy and a better workout. On Xenadrine Hardcore’s label it says:

"Recommended Use: As a dietary supplement: In the morning, take 2 capsules with breakfast or 30 minutes prior to training, and 2 capsules mid to late afternoon."

The total caffeine content in one serving, 2 capsules, is 360 mg! That’s 720 mg per day if you were to take it once in the morning and afternoon. Recall, the RDA of caffeine per day is 300 mg.

On Hydroxycut Hardcore’s label, it says:

"Recommended Use: As a dietary supplement take 3 capsules with an 8 oz glass of water 2 times daily, approximately 30 to 60 minutes before meals. On days of your workout, take 1 of these servings before the workout."

Nutrex Lipo 6’s label says:

"For Increased Energy: Take 2 liqui-caps 30 minutes prior to workout."

Unfortunately, the words “workout,” or “training,” (as well as the laymen’s version of “exercise”) are very general terms that do not convey the intensity of your exercise. Some people may say that they “workout” and their definition for the workout is a 2-mile walk or a low-sweat-producing weight routine. That is fine for them. Those individuals could take a product like Hydroxycut Hardcore and not worry about their heart rate getting too high. But for the individual who has been doing high-intensity weight training in conjunction with high-intensity sprints and weight circuits, there is a different definition to the word “workout” or “training.”

Many of the pre-workout and weight loss products are marketed to the ever-popular bodybuilding population. These workouts usually involve a moderate-intensity weight set of anywhere from 8-12 reps with 1-2 minutes of rest following the set. During this set, an individual’s heart rate can come down. Therefore, they may not feel the potential ill effects of taking a caffeine-containing weight-loss or pre-workout supplement during these exercise routines.

Also, a number of these companies have you take their product 30-60 minutes prior to a meal instead of prior to the workout. Trim Spa and other versions of Hydroxycut and Xenadrine have done this. This is because caffeine and a number of other stimulants in combination with caffeine have an appetite suppressing effect, causing you to eat less and/or feel satisfied sooner. Whether or not these products succeed in improving body composition goes beyond the scope of this article, but it is useful for you to understand why these companies make their recommendations.

I have seen the ill-effects of these "fat burner" supplements first hand. i was coaching a one of FIT's Crossfit classes, and the workout was three rounds of: 1000m Row, 50 Thrusters with 45 lbs., and 30 Kipping Pull-Ups - an enduring metabolic workout.

A fit man in his late 20's was complaining to me about how he just could not push himself as well as he wanted. He said he felt like he was not getting any oxygen into his lungs. He could not explain why. After the workout, he felt horrible, he took a long time to finish, and he later admitted that he took Hydroxycut (I do not know which version) prior to his workout. He was shocked to learn that it was probably the Hydroxycut that made him feel like garbage when he thought he was doing a good thing by taking something that was supposed to help him have a "better" workout.

An indiviudal's sensitivity to caffeine must always be considered. The textbooks say the half-life of caffeine —the time required for the body to eliminate one-half of the total amount of caffeine consumed at a given time —varies widely among individuals according to such factors as age, liver function, pregnancy, some concurrent medications, and the level of enzymes in the liver needed for caffeine metabolism. In healthy adults, caffeine's half-life is approximately 3–4 hours. In women taking oral contraceptives this is increased to 5–10 hours, and in pregnant women the half-life is roughly 9–11 hours. Therefore, some trial-and-error must be used when individuals are trying to determine the ideal dose to enhance their training. They must consider the type of training (such as Olympic-weightlifting versus high-intensity metabolic training) and not get set on a single dose, such as a dose of a pre-workout supplement, as the "end-all-be-all workout enhancer" for every workout. Perhaps it would be better to take after their training to wake them up from the exhausting workout they completed.

Summary

Caffeine can be beneficial for enhancing a workout, but it is largely dependent on the intensity of the exercise, the individual’s sensitivity to caffeine, and the amount of caffeine ingested. The original study I cited only used a single amount of 200 mg caffeine to blunt blood flow. Lesser amounts of caffeine (as found in a single cup of coffee or a diet soda) might still bring about the mental focus for the workout without a feeling of suffocation while improving exercising performance, depending on the type of exercise.

Also, the subjects in the first study were at various fitness levels that performed the exercise test at 78% and 98% of their predicted workloads. More fit individuals might be able to handle the higher intensity of a workout with caffeine versus other less fit individuals.

Both of the above points need further research to make a conclusive statement on the recommendations for using caffeine to individuals while exercising.

In 2005, only 1 year after taking caffeine off of the banned substance list, WADA started re-investigating caffeine’s effects in sports. WADA is said to be alarmed at the increasing use among sportsmen who say they are using it for its performance enhancement. It makes one question: if caffeine doesn’t work, why are so many competitive athletes taking it to get an edge? As of now, caffeine is still off of the list, so it is a legal substance for international athletes to take.

The take home message is: Be aware of the amount of caffeine you are ingesting in relation to your workout. The caffeine may be in the form of a tablet or powder or a beverage, such as coffee, energy drink, or soda, but it may have deleterious effects on your exercise performance.

Below is a list of common nationally-marketed sodas with their lesser known caffeine values:

IGA Cola = 4.9 mg/12 oz
Sam's Cola = 12.7 mg/12 oz
Coca-Cola = 33.9 mg/12 oz
Sam's Diet Cola = 13.3 mg/12 oz
Diet Coke = 46.3 mg/12 oz
Dr Thunder = 30.6 mg/12 oz
Pepsi = 38.9 mg/12 oz
Diet Dr Thunder = 29.9 mg/12 oz
Diet Pepsi = 36.7 mg/12 oz
Mountain Lightning = 46.5 mg/12 oz
Dr Pepper = 42.6 mg/12 oz
Diet Dr Pepper = 44.1 mg/12 oz
Mountain Dew = 54.8 mg/12 oz
Diet Mountain Dew = 55.2 mg/12 oz
Vault Zero = 74 mg/12 oz

Source: Chou, K.H., Bell L.N., J Food Sci. 2007 Aug;72(6):C337-42.

For any questions or a list of references, please email at scott@focusedtrainers.com.

Until next time…