All About Caffeine - The Muscle PhD

All About Caffeine

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Caffeine is easily the most commonly consumed drug around the world with beverages like coffee, soda, energy drinks, and espresso running rampant in our convenience stores and kitchens. While most people rely on a caffeinated beverage to act as their, “go-go juice,” athletes have long depended on caffeine for performance enhancement and focus during training and competition. In this piece, we’ll go over what caffeine is, how it can help performance, and if there’s a specific form or source of caffeine that might be best for your goals. Let’s get started.

What is Caffeine? How does it Work?

Caffeine is the most commonly used drug in the entire world, and with few negative side effects or long-term health consequences (6), this popularity is largely deserved. Most people use caffeine for that morning or mid-day pick-me-up, but athletes have actually been using caffeine to improve performance for decades (if not even longer). In fact, caffeine was recommended to be banned from use in sport all the way back in 1939 (6). Just about everyone has had some sort of experience with caffeine, so it’s worth discussing what it actually is as well as its method of action.

Caffeine is found in several plant sources with the most common being coffee beans; various teas and even cacao also have natural caffeine content. Caffeine is considered a stimulant, meaning it “energizes” us compared to substances like alcohol, which are considered, “depressants.” How does caffeine energize us?

In short, there’s a few theories but the one that makes the most sense is that caffeine blocks adenosine receptors in the brain (6,7). When adenosine interacts with receptors in the brain, it promotes drowsiness and relaxation. Since caffeine competes for this binding location, it causes the exact opposite – alertness and energy. This inhibition of adenosine can also impact hormones throughout the body; we often also see an increase in blood levels of epinephrine when people take caffeine. Epinephrine is more commonly referred to as, “adrenaline,” and causes our heart rate to increase, helps our muscles produce more force, and even increases our metabolism. Check out our Get Psyched article here for more info on adrenaline.

Caffeine has also been shown to increase pain tolerance (6). To this end, we see many OTC pain medications containing caffeine to help alleviate symptoms of pain. This is another reason why athletes and bodybuilders love caffeine so much; the burn isn’t quite as painful when you’re taking caffeine!

Lastly, we’ll touch on this more in the next section, but caffeine can also improve the performance of the heart through a unique interaction with the muscle cells of the heart. Cardiac muscle fibers have a few similarities to skeletal muscle; however, we have more conscious control of skeletal muscle which helps us produce a wide range of force with our skeletal muscles. All types of muscle fibers adhere to a few different laws, one of which being the Length-Tension relationship. This relationship simply states that a muscle fiber will produce x-amount of active force at a specific length – this curve is shaped like an upside-down U with the lowest levels of active force occurring at extremely short and long fiber lengths.

While that sounds complicated, this is one reason why our heart can pump more forcefully during exercise. When our heart fills with more blood, it stretches the muscle fibers of the heart to a greater degree than at rest. This causes the muscle fibers of the heart to contract with more force which pumps more blood and delivers more oxygen to our muscles. However, cardiac muscle fibers are also dependent on calcium concentration when it comes to force production (2). A suboptimal level of calcium in these muscle fibers can impair contraction, reducing force and overall cardiac output. Caffeine can actually help increase the calcium concentration and sensitivity in cardiac muscle fibers which helps them continue to produce high levels of force, even in exhaustive exercise (1). Essentially, it’s a complex way to say that caffeine helps our heart pump more blood!

Effects on Endurance Performance

Endurance exercise is one of the most common sports/hobbies in which caffeine is used. Studies consistently show a clear benefit of caffeine ingestion before training or competition, but positive effects can be mediated by variables such as dosage, nutrition status, and even timing (3). Caffeine can improve endurance performance by many of the effects we touched on above – increasing the contractility of cardiac muscle fibers, improving alertness, and modifying circulating hormone levels.

Again, the most important action of caffeine when it comes to endurance performance is probably its ability to compete for adenosine receptors. Since adenosine can contribute to drowsiness and fatigue, this can inhibit muscle performance and even influence central nervous system fatigue, which makes it harder to activate our muscles. In turn, this leads to an increase perception of both exertion and pain, and pretty soon, you want to quit exercising. This is why caffeine has consistently been shown to improve performance in tests that include either distance or time to exhaustion (3). While these tests aren’t always the most scientifically-sound, they help us gather more data on how caffeine can improve performance.

In addition, we know that caffeine ingestion can increase metabolic rate due to its effects on various hormones (6). However, caffeine can also promote fatty acid oxidation, which improves our ability to use fat as fuel (3). Since fat is a primary fuel source in long distance, low-to-moderate intensity exercise, increasing fat oxidation can help improve performance in these workouts.

Effects on Strength Performance

As with most exercise or nutrition-related research, the majority of studies utilizing caffeine include an endurance or cardio protocol, rather than strength training. However, more recent research has delved into the effects of caffeine on strength and power performance. Multiple studies have shown caffeine to improve strength and power performance, but, interestingly enough, caffeine may be more effective for improving upper body strength than lower body strength (7).

How can caffeine increase strength? Obviously, alertness and overall arousal play a role – if you’re fatigued or feeling down before taking caffeine, you’re going to experience a strength boost. However, caffeine’s main role in strength is probably through increasing muscle activation. Since caffeine blocks the action of adenosine, it is likely that we are better able to recruit our muscles to perform heavy or powerful lifting (7). Caffeine can affect multiple aspects of training from both a psychological (energy/focus) and physiological standpoint (muscle recruitment and fatiguability).

Why do studies not show a consistent increase in lower body strength from caffeine? We have to remember that studies are limited by the scientific method, so they may not always apply perfectly to real world training. When it comes to strength testing the lower body, movements are typically more complex and require more training experience and skill compared to upper body movements. Since most studies use untrained or moderately trained subjects, it’s hard to compare upper and lower body strength tests on an apples-to-apples basis as lower body strength tests may not be as reliable.

The limitations of science also apply to gender differences between caffeine response. We have no reason to think there’d be significantly different effects between men and women taking caffeine, but unfortunately, we don’t have much data on the effects of caffeine with female subjects (7). If anyone out there is trying to think of a thesis or dissertation project, this might be a good spot to start!

In addition, we don’t have much data on populations other than young adults. It remains to be seen if older adults will have a different response to caffeine ingestion, but I have a hunch that caffeine might be even more effective for older populations, especially when it comes to improving strength and fatiguability.

Dosage and Safety

Studies have been pretty consistent in showing that the effective dosage for caffeine is somewhere between 3mg/kg of bodyweight and 6mg/kg of bodyweight (3,7). For a 200lb individual, that would equate to a range of 272-545mg. It’s important to remember, though, that this doesn’t mean you have to have this much caffeine – some people may be more sensitive and don’t need that much. I used to be a 2-3 scoops of pre-workout kind of guy because I needed 4-500mg of caffeine to get a boost. Now I stick with about 150mg of caffeine and get plenty energized off of that. These are anecdotes, of course, but keep in mind that the 3-6mg/kg is a recommendation, not a rule. Some people might feel energized off of a single cup of coffee (roughly 100mg of caffeine), but the noticeable objective performance benefits probably begin around 3mg/kg of bodyweight.

How should you time caffeine around your workout? I’d recommend taking caffeine about 30-60 minutes before training. We typically see peak blood levels around 60-minutes after consumption (6) which is why we recommend this timing. I’d avoid taking caffeine after your workout as caffeine can actually impair insulin sensitivity (12) and cause vasoconstriction (6) – both are factors we don’t want when trying to recover from training!

When it comes to safety, caffeine really doesn’t have any long-term health concerns or cause any complications (6). This, of course, is referring to healthy populations with no underlying conditions. If you have any kind of cardiovascular disease or metabolic disease, I’d check with your physician before taking caffeine. In addition, caffeine can worsen symptoms of anxiety and nervousness in some people (11), so if you’re prone to anxiety, caffeine might not be the best bet for you. Lastly, I’d avoid taking caffeine close to bedtime as it can impair sleep quality (11). Sleep is much more important for performance improvements than any supplement could ever be, so make sure you don’t mess with your sleep schedule!

Tolerance is another issue when it comes to caffeine. Over time, we start to adapt to our daily caffeine dose and no longer get the same “boost” out of that dose. This leads many people to simply up the dose – hence why I was taking 2-3 scoops of pre-workout back in the day! However, even as little as a 7-day caffeine break can help bring your sensitivity back so you don’t have to buy a new tub of pre-workout every 2-weeks. How fast can we build a tolerance to caffeine? In as little as 15-days of consistent use, unfortunately (9).

How can we reduce the development of tolerance? The easiest way is to simply make sure you’re not taking caffeine every day [insert screaming emoji here]. I know this sounds impossible, but it will help keep your sensitivity in check. If that’s just not possible, try to plan a week out of every month or two where you swear off of caffeine for the entire week. Again, that’s probably going to be an awful week for you, but it will help keep tolerance at bay!

What Form of Caffeine is Best?

We know that we can get caffeine from multiple sources; coffee, pills, chocolate, etc. Is there a best form for exercise? Initial studies suggested that caffeine sourced from coffee might not be as effective as the anhydrous (pill) form of caffeine. It was theorized that some of the other bioactive components of coffee might interfere with caffeine’s effects (4). However, later studies were not able to replicate those results (8), so it might not be as big of a deal as we initially thought.

Another common source of caffeine is tea – especially green tea. However, some have wondered if green tea is actually an effective source of caffeine since it also contains the amino acid, L-theanine, which promotes relaxation. We don’t have a ton of information regarding this combination in the realm of exercise performance, but studies do show that L-theanine can counteract some of the negative side effects from caffeine use, like anxiety or jitters (10). Therefore, if you considered giving up caffeine use due to the side effects, give green tea a shot for a potentially smoother rush.

Overall, I don’t think there’s a specific form of caffeine that’s going to have magical effects compared to other forms. My best advice would be to stick to whatever’s most convenient for you, whether that be a preworkout drink, caffeine pills, or a mug of coffee.


All-in-all, caffeine is one of the most effective supplements for athletes looking for a performance boost. Most of the research on caffeine examines the acute effects of caffeine consumption, but if you reap these benefits throughout a long-term training program, you’re going to see improved gains. Do your best to utilize a strategy that promotes sustained sensitivity to caffeine – whether you ensure you don’t take it every day or you take a week off every month or two is up to you. Long-term use of caffeine is perfectly safe, just double check with your physician if you have any pre-existing conditions. Lastly, any form of caffeine is probably going to provide a boost both in and out of the gym, so use whatever form works best for you!


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  2. Eisner, D. A., Caldwell, J. L., Kistamás, K., & Trafford, A. W. (2017). Calcium and excitation-contraction coupling in the heart. Circulation Research, 121(2), 181-195.
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  11. Ruiz-Moreno, C., Lara, B., Salinero, J. J., de Souza, D. B., Ordovás, J. M., & Del Coso, J. (2020). Time course of tolerance to adverse effects associated with the ingestion of a moderate dose of caffeine. European Journal of Nutrition, 1-10.
  12. Shi, X., Xue, W., Liang, S., Zhao, J., & Zhang, X. (2016). Acute caffeine ingestion reduces insulin sensitivity in healthy subjects: a systematic review and meta-analysis. Nutrition Journal, 15(1), 103.

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