Caffeine is a central nervous system stimulant found in coffee, tea, chocolate, soda, and pre-workouts. Research shows benefits for both endurance and power performance.
Caffeine’s half-life (the time it takes the body to eliminate one half of the caffeine dose) is anywhere from 1.5-9 hours depending on various factors such as obesity, pregnancy, smoking, etc, according to the National Academy of Sciences. Humans absorb 99% of caffeine, it's metabolized in the liver and peak blood concentrations can be found 15-120 minutes after oral consumption.
What makes caffeine so hard to analyze is the fact that everyone reacts differently to it and the studies use a variety of doses. Nonetheless, here’s a primer on the effects of caffeine.
ERGOGENIC FOR ENDURANCE
Caffeine’s role in aiding endurance performance isn’t 100% clear but one theory is that caffeine causes the body to use fat as fuel resulting in the slowing of glycogen (stored sugar) depletion. This slowed depletion delays fatigue during aerobic exercise. A 2014 Journal of Exercise Nutrition & Biochemistry study found that an energy drink containing 2.5mg/kg body weight increased the time to exhaustion during a treadmill running test, meaning the participants were able to run for longer versus the control group.
The researchers in an International Journal of Sports Nutrition & Exercise Metabolism study used an energy drink with three of the same ingredients as C4 Ultimate Carbonated: caffeine, taurine, and B Vitamins. The study participants cycled for 120 minutes at a submaximal pace (61-75% of V02max), drinking an energy drink with just carbohydrates and electrolytes, the same drink plus the three aforementioned ingredients, or placebo every 15 minutes. People who took the drink with everything–the carbs, electrolytes, caffeine, etc–did more total work on the bike compared to just the carbs/electrolytes and placebo.
HELPFUL DURING POWER SPORTS
Caffeinated energy drinks have been shown to be ergogenic during short-duration, high-intensity exercise due to an increased power production. A 2013 Amino Acids study found that a pre-workout drink with 3mg/kg of bodyweight improved female Rugby players’ performance, namely their running speed and jump height. Coincidentally, another study in the same journal on females and energy drinks found similar results. An energy drink with 3mg/kg of body weight resulted in a higher jump and faster running speed.
There are other studies that show power improvements in elite Judo athletes and competitive swimmers too. These power benefits likely apply to a sport like CrossFit or Obstacle Course Racing where a short burst of energy is required.
IT WORKS FOR WEIGHTLIFTING
Caffeine’s impact on weightlifting for the purpose of muscle building hasn’t been studied much in humans. After all, caffeine isn’t the go-to supplement to make gains like whey protein or creatine. Nonetheless, caffeine has been shown to delay fatigue and help lifters get more reps.
According to a Journal of Sports Science & Medicine study, a pre-workout beverage with caffeine, taurine, beta-alanine and other ingredients helped guys crank out more reps on the barbell back squat and barbell bench press compared to a placebo. Power output during the four sets was greater after taking the supplement too.
No matter what your fitness goal or your workout, if it requires energy output, caffeine–especially when combined with other performance ingredients–can make a world of difference.