Repeated testing for the assessment of individual response to exercise training

Observed response to regular exercise training differs widely between individuals even in tightly controlled research settings. However, the respective contributions of random error and true interindividual differences as well as the relative frequency of non-responders are disputed. Specific challenges of analyses on the individual level as well as a striking heterogeneity in definitions may partly explain these inconsistent results. Repeated testing during the training phase specifically addresses the requirements of analyses on the individual level. Here we report a first implementation of this innovative design amendment in a head to head comparison of existing analytical approaches. To allow for comparative implementation of approaches we conducted a controlled endurance training trial (one year walking/jogging 3 days/week for 45 min with 60% heart rate reserve) in healthy, untrained subjects (n=36, age=46{plus minus}8; BMI 24.7{plus minus}2.7; VO2max 36.6{plus minus}5.4). In the training group additional VO2max tests were conducted after 3, 6 and 9 months. Duration of the control condition was 6 months due to ethical constraints. General efficacy of the training intervention could be verified by a significant increase in VO2max in the training group (p<0.001 vs. control). Individual training response of relevant magnitude (>0.2*baseline variability in VO2max) could be demonstrated by several approaches. Regarding the classification of individuals only 11 out of 20 subjects were consistently classified, demonstrating remarkable disagreement between approaches. These results are in support of relevant interindividual variability in training efficacy and stress the limitations of a responder classification. Moreover, this proof-of-concept underlines the need for tailored methodological approaches for well-defined problems.