Endurance training and maximal oxygen consumption with ageing: Role of maximal cardiac output and oxygen extraction

Background The increase in maximal oxygen consumption (VO2max) with endurance training is associated with that of maximal cardiac output (Q(max)), but not oxygen extraction, in young individuals. Whether such a relationship is altered with ageing remains unclear. Therefore, we sought systematically to review and determine the effect of endurance training on and the associations among VO2max, Q(max) and arteriovenous oxygen difference at maximal exercise (Ca-vO(2max)) in healthy aged individuals. Design and methods We conducted a systematic search of MEDLINE, Scopus and Web of Science, from their inceptions until May 2015 for articles assessing the effect of endurance training lasting 3 weeks or longer on VO2max and Q(max) and/or Ca-vO(2max) in healthy middle-aged and/or older individuals (mean age 40 years). Meta-analyses were performed to determine the standardised mean difference (SMD) in VO2max, Q(max) and Ca-vO(2max) between post and pre-training measurements. Subgroup and meta-regression analyses were used to evaluate the associations among SMDs and potential moderating factors. Results Sixteen studies were included after systematic review, comprising a total of 153 primarily untrained healthy middle-aged and older subjects (mean age 42-71 years). Endurance training programmes ranged from 8 to 52 weeks of duration. After data pooling, VO2max (SMD 0.89; P<0.0001) and Q(max) (SMD 0.61; P<0.0001) were increased after endurance training; no heterogeneity among studies was detected. Ca-vO(2max) was only increased with endurance training interventions lasting more than 12 weeks (SMD 0.62; P=0.001). In meta-regression, the SMD in Q(max) was positively associated with the SMD in VO2max (B=0.79, P=0.04). The SMD in Ca-vO(2max) was not associated with the SMD in VO2max (B=0.09, P=0.84). Conclusions The improvement in VO2max following endurance training is a linear function of Q(max), but not Ca-vO(2max), through healthy ageing.