Acute effects of fasted training on physical performance and training stress in highly-conditioned subjects

Background: Over the years, the effects of fasted training on the performance of competitive and amateur athletes has gathered increasing attention. This is mostly due to the theoretical vantages regarding the greater reliance on fatty acids as the energetic substrate and the increased lipolysis in adipose tissue during exercise in the fasted state. At the same time, fasted training is especially preferred by amateur athletes, since it allows them to train early in the morning before work. Questions/purposes: The present study aims to evaluate the effects of a single training session in fasting conditions on physical performance, body composition, and training stress in competitive athletes. Methods: Twelve competitive male athletes in different sports were firstly scored for anthropometric measurements (weight, height, BMI), body composition (Bioelectrical Impedance Analysis, BIA, Akern srl, Italy), salivary cortisol levels (Immunoenzymatic Assay, Diametra srl, Italy), the velocity at maximal oxygen uptake (treadmill incremental vV̇O2max test) and maximal dynamic strength by two dif erent exercises, namely 1-RM Repetition Maximum by Brzycki formula in both bench press and lat pull-down with pronated grip. Each subject randomly performed two equal-volume single training sessions both in normal conditions (i.e. no fasting) and after 12-14 hours of fasting. During the training sessions, the Heart Rate and the Ratings of Perceived Exertion (Borg CR10 scale) were monitored both during the training session and at the end of each session. Results: No differences were found between the training session performed either in normal or fasted conditions regarding all the measurements except for the Heart Rate in the fi rst 5 minutes of aerobic exercise (-3,2% in fasted training, p<0.05) and the lat pull-down maximal strength test (-19% in fasted training, p<0.05); after the training session, salivary cortisol levels were 49% higher in fasted state compared with no fasted condition, though being not statistically significant (p=0.07); with reference to BIA variables, the phase angle showed a slight but significant decrease (-1.3%, p<0.05) at the end of the training session in the fasted conditions, while a minor reduction in the resistance occurred in fasted vs. no fasted training (-1.4%, p<0.05 vs -3.5%, p<0.002, respectively), suggesting a higher catabolic state. Conclusion: In highly-conditioned subjects, the acute response to a single standard training session in fasting conditions does not show excessive athletic and metabolic body stress but rather induces a reduction of dynamic strength and higher catabolism at the end of the training.