Caffeine is a powerful substance that can improve both your physical and mental performance.

A single dose can significantly improve exercise performance, focus, and fat burning (1, 2, 3).

The U.S. Special Forces even use it to enhance performance and awareness.

Caffeine is found in many foods and beverages, and nearly 90% of the U.S. population consumes it on a regular basis (4).

This article explains caffeine’s benefits for exercise performance.

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How caffeine works

Caffeine is rapidly absorbed into your bloodstream, and blood levels peak after 30–120 minutes. Caffeine levels remain high for 3–4 hours and then start to drop (1).

Unlike most substances and supplements, caffeine can affect cells throughout your body, including muscle and fat cells, as well as cells within your central nervous system (5).

For this reason, caffeine’s effects are quite varied. These include:

• The nervous system. Caffeine activates areas of your brain and nervous system to improve focus and energy while reducing tiredness (2, 6).
• Hormones. Caffeine increases circulating epinephrine (adrenaline), the hormone responsible for the “fight or flight” response, which can increase performance (7).
• Fat burning. Caffeine may increase your body’s ability to burn fat via lipolysis, or the breakdown of fat in fat cells (3, 8).
• Endorphins. Beta-endorphins can increase feelings of wellness and give you the exercise “high” that people often experience after working out (9, 10).
• Muscles. Caffeine may improve muscle performance through activation of the central nervous system; however, the exact mechanisms are unclear (11).
• Body temperature. Caffeine has been shown to increase thermogenesis, or heat production, which raises your body temperature and may help you burn more calories (12).
• Glycogen. Caffeine may also spare muscle carb stores, primarily due to increased fat burning. This can enhance endurance performance (13, 14).

Caffeine is eventually broken down in the liver (1).

Summary

Caffeine can easily pass throughout your body. It has varied effects on your hormones, muscles, and brain.

Caffeine and endurance performance

Caffeine is the go-to supplement for many athletes.

Due to its positive effects on exercise performance, some organizations — such as the National Collegiate Athletic Association (NCAA) — have even started to ban it in high doses.

One large review of studies found that caffeine modestly improves endurance when used in moderate doses of 1.4–2.7 mg per pound (3–6 mg per kg) of body weight (15).

In one study, trained cyclists who consumed either 100- and 200-mg doses of caffeine along with a carbohydrate-electrolyte solution late in exercise completed a time trial faster than those who consumed only the carbohydrate-electrolyte solution.

What’s more, cyclists who consumed the 200-mg dose of caffeine completed the time trial faster than those who consumed the 100-mg dose (16).

Other research examined the effect of coffee due to its naturally high levels of caffeine. Research suggests both caffeine and caffeinated coffee produce similar benefits for endurance exercise performance (17).

Some research suggests that a genetic variation that affects how you metabolize caffeine may determine the extent to which caffeine improves your endurance performance.

In one study, competitive male athletes consumed either 0.9 or 1.8 mg of caffeine per pound (2 or 4 mg per kg) of body weight or a placebo before completing a 6.2-mile (10-km) cycling time trial.

All who consumed caffeine experienced performance improvements. Although, those with the genetic variation experienced significantly greater dose-dependent improvements in endurance performance than those without the genetic variation (18).

Summary

Caffeine and coffee can both significantly improve performance for endurance athletes. A genetic variation may determine the extent to which caffeine improves your endurance performance.

Caffeine and high intensity exercise

Studies on caffeine’s effects on high intensity exercise have turned up mixed results.

Caffeine has impressive benefits for trained athletes, but it may offer less significant benefits for beginners or those who are untrained (19).

In one small, well-designed study, men who participated in high intensity cycling felt less fatigued and were able to continue cycling longer after consuming 1.8 mg of caffeine per pound (4 mg per kg) of body weight, compared with a placebo (20).

However, in another study, supplementing with 300 mg of caffeine or coffee along with creatine did not improve sprint performance in physically active males (21).

A review of studies showed that consuming 1.4–2.7 mg of caffeine per pound (3–6 mg per kg) of body weight 30–90 minutes prior to high intensity exercise reduced participants’ experience of exertion (22).

Summary

For high intensity sports like cycling or swimming, caffeine may benefit trained athletes more than untrained individuals.

Caffeine and strength exercises

Research is still emerging on the use of caffeine in strength or power-based activities.

Although several studies have found a positive effect, the evidence is inconclusive (23, 24, 25).

In one study, 12 participants performed bench presses after consuming 1.4 mg of caffeine per pound (3 mg per kg) of body weight or a placebo. After consuming caffeine, participants demonstrated significantly increased force and power output compared with a placebo (26).

In another study, 12 people who regularly consumed caffeine consumed either a placebo or 1.4 or 2.7 mg of caffeine per pound (3 or 6 mg per kg) of body weight.

Compared with a placebo, consuming caffeine increased mean power output and mean bar velocity when performing 5 sets of a bench press throw (27).

However, in one small but well-designed study, ingestion of caffeine prior to a workout did not significantly affect muscle strength, as measured by handgrip strength, among CrossFit athletes (28).

Another study looked at whether consuming a high dose of caffeine improves muscle strength in male athletes who regularly drank coffee. Taking a high dose of caffeine did not significantly affect their maximum bench press strength compared with a placebo (29).

Overall, studies indicate that caffeine may provide benefits for power-based activities, but more research is needed to confirm this.

Summary

Caffeine may help improve performance in strength or power-based exercises, but study results are mixed.

Caffeine and fat loss

Caffeine is a common ingredient in weight loss supplements.

Caffeine induces the breakdown of fat in fat cells, increases your body’s production of heat, and increases fat oxidation in people with an average weight, overweight, and obesity (30).

Caffeine also modestly increases your daily calorie expenditure (30).

Plus, consuming caffeine before exercise may significantly increase the release of stored fat.

One review of studies showed that consuming 1.4–2.7 mg of caffeine per pound (3–7 mg per kg) of body weight significantly increased fat burning during exercise, especially among sedentary or untrained individuals (3).

However, no evidence suggests that caffeine consumption promotes significant weight loss.

Summary

Caffeine can help release stored fat from fat cells, especially before and at the end of a workout. It can also help you burn more calories.

How to supplement with caffeine

There are several things to keep in mind when supplementing with caffeine.

If you regularly consume coffee, energy drinks, caffeinated soda, or dark chocolate, you may experience fewer benefits from caffeine supplements. This is because your body has developed a tolerance to caffeine (31).

Research suggests both caffeine anhydrous supplements and regular coffee provide benefits for exercise performance (17).

What’s more, coffee provides antioxidants and various additional health benefits.

When supplementing with caffeine, the dose is often based on body weight, set at around 1.4–2.7 mg per pound (3–6 mg per kg) of body weight. This is about 200–400 mg for most people, although some studies use up to 600–900 mg (1).

Start at a low dose — around 150–200 mg — to assess your tolerance. Then increase the dose to 400 or even 600 mg to maintain a performance benefit.

Very high doses — 4.1 mg of caffeine per pound (9 mg per kg) body weight or more — are associated with unpleasant side effects and do not offer additional performance benefits (1).

If you wish to use caffeine for athletic performance, you should also save it for key events or races to maintain sensitivity to its effects.

For optimal performance, take it about 60 minutes before a race or event. However, make sure to test this protocol first if you’re not used to taking caffeine.

That said, the optimal timing may depend on the form of supplementation. For example, caffeinated chewing gums may be taken closer to the start of a race or event.

Summary

Consuming 200–400 mg of caffeine 60 minutes before a race or event can help maximize performance benefits.

Side effects of caffeine

At a sensible dose, caffeine can provide many benefits with few side effects. However, it may be unsuitable for some people.

Here are some common side effects of too much caffeine:

• increased heart rate
• anxiety
• dizziness
• insomnia or sleep disruption
• irritability
• tremors
• stomach discomfort

High doses of 600 mg — the amount in about 6 cups of coffee — have been shown to increase tremors and restlessness, especially for people who are not used to caffeine.

People who are prone to anxiety may also want to avoid high doses (32).

Those with heart disease, high blood pressure, gastroesophageal reflux disease (GERD), and several other conditions, as well as people who are pregnant, should use caution when consuming caffeine and consult their doctor to determine whether caffeine is safe for them.

Timing may also matter, as late-night or evening caffeine can disrupt sleep. Try to avoid caffeine intake after 4 or 5 p.m.

Finally, you could become ill, or even die, if you overdose on extremely high amounts of caffeine. Do not confuse milligrams with grams when using caffeine supplements.

Summary

Caffeine is a fairly safe supplement at the recommended doses. It may cause minor side effects in some people and should be used with caution in individuals with heart disease, high blood pressure, GERD, and several other conditions.

The bottom line

Caffeine is one of the most effective exercise supplements available. It’s also very cheap and relatively safe to use.

Studies have shown that caffeine can benefit endurance performance, high intensity exercise, and power sports. However, it seems to benefit trained athletes the most.

The recommended dose varies by body weight, but it’s typically about 200–400 mg, taken 30–60 minutes before a workout.

Both caffeine anhydrous supplements and regular coffee provide performance benefits.