Endurance Training and (V) over dotO2max: Role of Maximal Cardiac Output and Oxygen Extraction

Purpose Although endurance training (ET) commonly augments maximal oxygen consumption (VO2max), it remains unclear whether such increase is associated with that of maximal cardiac output (Q(max)) alone or along with arteriovenous oxygen difference (a-VO2diff). Herein, we sought to systematically review and determine the effects of ET on VO2max, Q(max), and a-VO2diff 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 VO2max and Q(max) and/or a-VO2diff at maximal exercise in healthy young adults (mean age <40 yr). Meta-analyses were performed to determine standardized mean differences (SMD) in VO2max, Q(max), and a-VO2diff 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, VO2max (SMD = 0.75, P < 0.0001) and Q(max) (SMD = 0.64, P < 0.0001), but not a-VO2diff 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(max) was positively associated with the SMD in VO2max (B = 0.91, P = 0.007). The SMD in a-VO2diff at maximal exercise was not associated with the SMD in VO2max (B = 0.20, P = 0.40). Conclusions Based on a relatively small number of studies, improvement in VO2max following 5-13 wk of ET is associated with increase in Q(max), but not in a-VO2diff, in previously untrained to moderately trained healthy young individuals.