Caffeine can be a great tool for athletes of all abilities used to enhance performance. However, when abused (or not used as a tool), it can be a detriment to your training and racing.
What I typically recommend for caffeine use (if an athlete would like to use caffeine as a supplement) on both a macro, and micro level is as follows:
1) Keep total daily intake below 200mg unless its race day. This is the ADA recommendation (for healthy adults) and helps avoid receptor up-regulation that weakens the affect of caffeine when you really want to use the extra push. It also helps keep you from lying in bed each night with your eyes open.
2) Use it as a tool! That is, save coffee or caffeinated products for before/during, key intensity based workouts. Don’t waist it (and encourage receptor up-regulation) when just sitting around the office. What I have found, is that chronic usage during the day can really impact an athlete’s ability to performance best effort workouts in the evening due to a skewed perceived exertion. Like most drugs, you then need another big dose to even feel like yourself…not a good cycle!
3) During the day while not working out, if you need a pick up, consider using lighter caffeine products like green tea. This avoids the receptor up-regulation described above. Green tea also provides tremendous antioxidant properties which as athletes, is a really big plus to mitigate free radical damage produced by all of the aerobic oxidation that we create.
4) During the final two days before a key event, limit caffeine to 100mg at 2 days out, and 30mg the day before. This ensures that your race day boost is felt in a big way.
5) Increase caffeine intake throughout workouts and races, such that peak serum caffeine levels occur as your peripheral system becomes the most fatigued (ie, at the end of the session/race). Early caffeine consumption on long days (5+ hours) typically results in over pacing the early portion of the event/session and subsequently leads to a significant drop off in pace later in the day as the peripheral system becomes fatigued. Use caffeine to help continue stimulation of your core system as this fatigue sets in.
6) Lastly, excessive caffeine and/or coffee can really do a number on your gut…reducing your ability to absorb key nutrients, and also just plain irritate it. This is a common cause of race fueling difficulty (habitual caffeine intake) that many seem to miss.
In summary, caffeine can be a great, undeniable performance and training aid when used properly. However, it can also be a slippery slope that any serious athlete should avoid being pulled into. I hope these recommendation from both a macro (day to day) and micro (within each session) perspective help clear up some of the confusion (and/or my logic in this area).