Endurance Training and VO2max: Role of Maximal Cardiac Output and Oxygen Extraction

Abstract

© 2015 by the American College of Sports Medicine. Purpose Although endurance training (ET) commonly augments maximal oxygen consumption (VO<inf>2max</inf>), it remains unclear whether such increase is associated with that of maximal cardiac output (Q<inf>max</inf>) alone or along with arteriovenous oxygen difference (a-VO<inf>2diff</inf>). Herein, we sought to systematically review and determine the effects of ET on VO<inf>2max</inf>, Q<inf>max</inf>, and a-VO<inf>2diff</inf> at maximal exercise, and on their associations, in healthy young subjects. Methods We conducted a systematic search of MEDLINE, Scopus, and Web of Science (from their inception until September 2014) for articles assessing the effects of ET lasting ≥3 wk on VO<inf>2max</inf> and Q<inf>max</inf> and/or a-VO<inf>2diff</inf> at maximal exercise in healthy young adults (mean age <40 yr). Meta-analyses were performed to determine standardized mean differences (SMD) in VO<inf>2max</inf>, Q<inf>max</inf>, and a-VO<inf>2diff</inf> at maximal exercise between posttraining and pretraining measurements. Subgroup and meta-regression analyses were used to evaluate associations among SMD and potential moderating factors. Results Thirteen studies were included after systematic review, comprising a total of 130 untrained or moderately trained healthy young subjects (mean age, 22-28 yr). Duration of ET programs ranged from 5 to 12.9 wk. After data pooling, VO<inf>2max</inf> (SMD = 0.75, P < 0.0001) and Q<inf>max</inf> (SMD = 0.64, P < 0.0001), but not a-VO<inf>2diff</inf> at maximal exercise (SMD = 0.21, P = 0.23), were increased after ET. No significant heterogeneity was detected. With meta-regression, the SMD in Q<inf>max</inf> was positively associated with the SMD in VO<inf>2max</inf> (B = 0.91, P = 0.007). The SMD in a-VO<inf>2diff</inf> at maximal exercise was not associated with the SMD in VO<inf>2max</inf> (B = 0.20, P = 0.40). Conclusions Based on a relatively small number of studies, improvement in VO<inf>2max</inf> following 5-13 wk of ET is associated with increase in Q<inf>max</inf>, but not in a-VO<inf>2diff</inf>, in previously untrained to moderately trained healthy young individuals.