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Acute Ketone Supplementation and Exercise Performance: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Pedro L. Valenzuela, Javier S. Morales, Adrián Castillo-García, and Alejandro Lucia

Purpose: To determine the acute effects of ketone supplementation on exercise performance (primary outcome) and physiological and perceptual responses to exercise (secondary outcomes). Methods: A systematic search was conducted in PubMed, Web of Science, and SPORTDiscus (since inception to July 21, 2019) to find randomized controlled trials assessing the effects of acute ketone supplementation compared with a drink containing no ketones (ie, control intervention). The standardized mean difference (Hedges g) between interventions and 95% confidence interval (CI) were computed using a random-effects model. Results: Thirteen studies met all inclusion criteria. No significant differences were observed between interventions for overall exercise performance (Hedges g = −0.05; 95% CI, −0.30 to 0.20; P = .68). Subanalyses revealed no differences between interventions when analyzing endurance time-trial performance (g = −0.04; 95% CI, −0.35 to 0.28; P = .82) or when assessing the separate effects of supplements containing ketone esters (g = −0.07; 95% CI, −0.38 to 0.24; P = .66) or salts (g = −0.02; 95% CI, −0.45 to 0.41; P = .93). All studies reported increases in plasma ketone concentration after acute ketone supplementation, but no consistent effects were reported on the metabolic (plasma lactate and glucose levels), respiratory (respiratory exchange ratio, oxygen uptake, and ventilatory rate), cardiovascular (heart rate), or perceptual responses to exercise (rating of perceived exertion). Conclusions: The present findings suggest that ketone supplementation exerts no clear influence on exercise performance (from sprints to events lasting up to ∼50 min) or metabolic, respiratory, cardiovascular, or perceptual responses to exercise. More research is needed to elucidate if this strategy could provide ergogenic effects on other exercise types (eg, ultraendurance exercise).

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Is the Functional Threshold Power a Valid Surrogate of the Lactate Threshold?

Pedro L. Valenzuela, Javier S. Morales, Carl Foster, Alejandro Lucia, and Pedro de la Villa

Purpose: To analyze the relationship between functional threshold power (FTP) and the lactate threshold (LT). Methods: A total of 20 male cyclists performed an incremental test in which LT was determined. At least 48 h later, they performed a 20-min time trial, and 95% of the mean power output was defined as FTP. Participants were divided into recreational (peak power output < 4.5 W·kg−1; n = 11) or trained cyclists (peak power output > 4.5 W·kg−1; n = 9) according to their fitness status. Results: The FTP (240 [35] W) was overall not significantly different (effect size = 0.20; limits of agreement = −2.4% [11.5%]) from the LT (246 [24] W), and both markers were strongly correlated (r = .95; P < .0001). Accounting for the participants’ fitness status, no significant differences were found between FTP and LT (effect size = 0.22; limits of agreement =2.1% [7.8%]) in trained cyclists, but FTP was significantly lower than the LT (P = .0004, effect size = 0.81; limits of agreement =−6.5% [8.3%]) in recreational cyclists. A significant relationship was found between relative peak power output and the bias between FTP and the LT markers (r = .77; P < .0001). Conclusions: FTP is a valid field test-based marker for the assessment of endurance fitness. However, caution should be taken when using FTP interchangeably with LT, as the bias between markers seems to depend on the athlete’s fitness status. Whereas FTP provides a good estimate of LT in trained cyclists, in recreational cyclists, it may underestimate LT.

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Ultraendurance Exercise in a Renal Transplant Recipient: A Case Study

Sonsoles Hernández-Sánchez, Pedro L. Valenzuela, Javier S. Morales, Juan J. Carrero, Alejandro Lucia, and Jonatan R. Ruiz

Context: Exercise improves the commonly impaired physical fitness and cardiovascular health of transplant recipients. However, concerns remain about the safety of strenuous physical exercise in this population. Purpose: To describe the physiological effects of ultraendurance exercise in a renal transplant recipient. Methods: After a 25-week training program, a 31-year-old male with stage 3 chronic kidney disease who had undergone 2 kidney transplants participated in a 62-km (5600 m of positive altitude change) trail-running race. Blood and urine analyses were performed at baseline (24 h before the race), 4 days after the race, and at different time points up to 16 weeks postexercise. Results: The participant completed the race in 12 hours 18 minutes. No noticeable side effects were recorded during the whole study period, including the prerace training program. No major urine or blood alterations were observed after ultraendurance exercise, with glomerular filtration rate remaining steady during the study period. Conclusions: Ultraendurance exercise induced no adverse physiological effects in a well-trained young renal transplant recipient.