This study investigated the effect of the racemic β-hydroxybutyrate (βHB) precursor, R,S-1,3-butanediol (BD), on time-trial (TT) performance and tolerability. A repeated-measures, randomized, crossover study was conducted in nine trained male cyclists (age, 26.7 ± 5.2 years; body mass, 69.6 ± 8.4 kg; height, 1.82 ± 0.09 m; body mass index, 21.2 ± 1.5 kg/m2; VO2peak,63.9 ± 2.5 ml·kg−1·min−1; W max, 389.3 ± 50.4 W). Participants ingested 0.35 g/kg of BD or placebo 30 min before and 60 min during 85 min of steady-state exercise, which preceded a ∼25- to 35-min TT (i.e., 7 kJ/kg). The ingestion of BD increased blood D-βHB concentration throughout exercise (0.44–0.79 mmol/L) compared with placebo (0.11–0.16 mmol/L; all p < .001), which peaked 1 hr following the TT (1.38 ± 0.35 vs. 0.34 ± 0.24 mmol/L; p < .001). Serum glucose and blood lactate concentrations were not different between trials (all p > .05). BD ingestion increased oxygen consumption and carbon dioxide production after 20 min of steady-state exercise (p = .002 and p = .032, respectively); however, no further effects on cardiorespiratory parameters were observed. Within the BD trial, moderate to severe gastrointestinal symptoms were reported in five participants, and low levels of dizziness, nausea, and euphoria were reported in two participants. However, this had no effect on TT duration (placebo, 28.5 ± 3.6 min; BD, 28.7 ± 3.2 min; p = .62) and average power output (placebo, 290.1 ± 53.7 W; BD, 286.4 ± 45.9 W; p = .50). These results suggest that BD has no benefit for endurance performance.
David M. Shaw, Fabrice Merien, Andrea Braakhuis, Daniel Plews, Paul Laursen and Deborah K. Dulson
Ana C. Holt, Daniel J. Plews, Katherine T. Oberlin-Brown, Fabrice Merien and Andrew E. Kilding
Purpose: To determine the effect of different high-intensity interval-training (IT) sessions on the postexercise recovery response and time course across varying recovery measures. Methods: A total of 13 highly trained rowers (10 male and 3 female, peak oxygen uptake during a 6-min maximal test 4.9 [0.7] L·min−1) completed 3 IT sessions on a rowing ergometer separated by 7 d. Sessions consisted of 5 × 3.5 min, 4-min rest periods (maximal oxygen uptake [VO2max]); 10 × 30 s, 5-min rest periods (glycolytic); and 5 × 10 min, 4-min rest periods (threshold). Participants were instructed to perform intervals at the highest maintainable pace. Blood lactate and salivary cortisol were measured preexercise and postexercise. Resting heart-rate (HR) variability, post-submaximal-exercise HR variability, submaximal-exercise HR, HR recovery, and modified Wingate peak and mean power were measured preexercise and 1, 10, 24, 34, 48, 58, and 72 h postexercise. Participants resumed training throughout the measurement period. Results: Between-groups short-term response differences (1 h post-IT) across IT sessions were trivial or unclear for all recovery variables. However, post-submaximal-exercise HR variability demonstrated the longest recovery time course (threshold = 37.8 [14.2], glycolytic = 20.2 [11.0], and VO2max = 20.6 [15.2]; mean [h] ± confidence limits). Conclusion: Short-term responses to threshold, glycolytic, and VO2max IT in highly trained male and female rowers were similar. Recovery time course was greatest following threshold compared with glycolytic and VO2max-focused training, suggesting a durational influence on recovery time course at HR intensities ≥80% HRmax. As such, this provides valuable information around the programming and sequencing of high-intensity IT for endurance athletes.