Increased fat availability enhances the capacity of trained individuals toperform prolonged exercise

Methods: After a familiarization period, six well-trained males participate d in a diet and exercise regimen lasting 9 d and comprising three cycling t ests to exhaustion. A work rate was selected during the familiarization per iod that would result in fatigue after approximately 90-100 min at an ambie nt temperature of 10 degrees C (i.e., approximately 75% of (V) over dot O-2 max). The first exercise test was a depletion trial and was preceded by a p eriod during which the subjects' normal diet was consumed. A prescribed 70% carbohydrate (CHO) diet was then consumed for 3.5 d. After this diet, a se cond exercise test was performed; one of two isoenergetic experimental meal s was consumed 4 h before this test (70% CHO meal, CHO trial; or 90% fat me al, fat trial). The second exercise test was followed by a further 3.5-d pe riod on the high. CHO dirt. Four hours before the third test, subjects cons umed the other meal. Heparin was administered intravenously 30 min (1000 U) , 15 min (500 U), and 0 min (500 U) before exercise on the fat trial. Subje cts were assigned to the two meals in randomized order. Results: Time to ex haustion increased from 118.2 (12.4) min on the CHO trial to 127.9 (12.1) m in on the fat trial (P = 0.001). Although no difference in (V) over dot O-2 , RER, HR or RPE was found between trials, there was an earlier reduction i n RER and an earlier rise in RPE on the fat trial. No difference in total C HO oxidation was found between trials (383 +/- 70 g on the CHO trial and 36 2 +/- 59 g on the fat trial). Conclusions: These results suggest that incre asing fat availability immediately before exercise by acute fat feeding and heparin infusion can improve endurance exercise in a cool environment in w ell-trained individuals. This study was not intended to have immediate appl ication to the sports performance field but rather to contribute to our und erstanding of the factors that may limit endurance performance. Heparin inj ection to elevate plasma fatty acid concentration would not represent sound medical practice.