Effects of time-release caffeine containing supplement on metabolic rate,glycerol concentration and performance

This study compared caffeine pharmacokinetics,glycerol concentrations,metabolic rate,and performance measures following ingestion of a time-release caffeine containing supplement (trcaf) versus a regular caffeine capsule (caf) and a placebo (pl). following a double-blind,placebo-controlled,randomized,cross-over design,ten males (25.9 ± 3.2 y) who regularly consume caffeine ingested capsules containing either tr-caf,caf,or pl. blood draws and performance measures occurred at every hour over an 8-hour period. plasma caffeine concentrations were significantly greater (p < 0.05) in caf compared to tr-caf during hours 2-5 and significantly greater (p = 0.042) in tr-caf compared to caf at hour 8. there were no significant differences between trials in glycerol concentrations (p = 0.86) or metabolic measures (p = 0.17-0.91). physical reaction time was significantly improved for caf at hour 5 (p=0.01) compared to pl. average upper body reaction time was significantly improved for caf and tr-caf during hours 1-4 (p = 0.04 and p = 0.01,respectively) and over the 8-hour period (p = 0.04 and p = 0.001,respectively) compared to pl. average upper body reaction time was also significantly improved for tr-caf compared to pl during hours 5-8 (p = 0.004). tr-caf and caf showed distinct pharmacokinetics yielding modest effects on reaction time,yet did not alter glycerol concentration,metabolic measures,or other performance measures. © 2015,journal of sports science and medicine. all rights reserved.