Caffeine can improve your focus and endurance during your workout.
If you are going to be doing cardio, taking 250mg to 400mg of caffeine 45 to 60 minutes before your workout is a good range to get you started, depending on your body size and overall caffeine tolerance.
At this level of caffeine intake, you will experience increases in your vigilance with an improved ability to sustain your maximal endurance output.
This is about the amount of caffeine found in a 16 oz cup of coffee. More is not always better, as larger doses don’t necessarily yield greater effects.
When it comes to weight training, most people use caffeine before training to increase their focus and overall arousal state in order to hit the weight room as hard as possible. If this is your goal, have as much or as little caffeine as you need to hit beast mode.
Whether it is weight training or cardio, if you are truly looking to use caffeine as a performance enhancer, it would be prudent to cycle your intake since your body gets used to the effects of caffeine rather quickly.
Mike Roussell, Ph.D., is the Men's Health nutrition advisor. He holds a degree in biochemistry from Hobart College and a doctorate in nutrition from Pennsylvania State University. His research has been published multiple times in the American Journal of Clinical Nutrition.