Caffeine but Not Low-Carbohydrate Improves Exercise Capacity in Sedentary Adults Similar to Endurance Trained Athletes

Caffeine (CAF) and small amounts of carbohydrate (CHO) ingested or simply exposed to the oral cavity appear to delay fatigue during prolonged exercise, possibly through central nervous system mechanisms. However, this has been primarily documented in endurance trained (ET) athletes. PURPOSE: To determine if: 1) CAF and/or a low dose of CHO (equivalent to CHO contained in ergogenic mouth rinse and insufficient to trigger a peripheral metabolic response) improves endurance capacity in sedentary adults (SED) similar to ET and 2) potential ergogenic mechanisms differ based on fitness status. METHODS: Using a double-blind crossover design, ET and SED (n=12 each) completed four exercise trials consisting of 30 min cycling at 90% lactate threshold followed by cycling time to fatigue (TTF) at 105% lactate threshold. The following solutions were ingested after standardized 43 g CHO breakfast: CAF (3 mg/kg), low (<1%) CHO (LCHO), combined CAF+LCHO, and placebo (PLA). RESULTS: ET and SED did not differ in overall mean (±SD) TTF (23.8 ± 8.1 vs. 24.1 ± 11.3 min) but TTF improved (p<0.05) in CAF+LCHO versus LCHO. When averaging across both CAF treatments (CAF+LCHO and CAF), perceived exertion was lowered and TTF was increased by 21% (26.3 ± 10.4 vs. 21.7 ± 9.9 min) compared to the two no-CAF treatments (PLA and LCHO), but CAF did not alter muscle strength/activation. Blood glucose, lactate, and CHO oxidation were higher with CAF vs. no-CAF treatments. Fat oxidation was higher in ET compared to SED, but CAF did not alter fat oxidation. CONCLUSIONS: The ergogenic benefit and action of CAF appears to be independent of fitness status. The addition of LCHO ingestion, previously observed to act centrally, did not further augment benefits of CAF in the fed state.