Many of us are familiar with the high caffeine content in pre-workout supplements. However findings by Pedersen et al. (2008) (as cited by Beelen, Burke, Gibala & van Loon, 2010) reported a 66% greater increase in muscle glycogen synthesis when caffeine (2mg/kg/hr) was ingested concomitantly with carbohydrate (CHO; 1g/kg/hr) over 4 hours post exercise.
For greater repletion of CHO post workout, save your caffeine for use with carbohydrate post workout. This is a great strategy to utilize when doing a 2-a-day workout schedule to optimize performance in the second session.
Beelen, M., Burke, L. M., Gibala, M. J., & van Loon, L. J. C. (2010). Nutritional Strategies to Promote Postexercise Recovery Synthesis. International Journal of Sport Nutrition and Exercise Metabolism, 20, 515–533.