Abstract
One in five adults following physical activity guidelines are reported not demonstrating any improvement in cardiorespiratory fitness (CRF). Herein, we sought to establish whether CRF non-response to exercise training is dose-dependent, using a between- and within-subject study design. Seventy-eight healthy adults were divided into 5 groups ('1', '2', '3', '4' and '5') respectively comprising 1, 2, 3, 4 and 5 × 60 min exercise sessions per week but otherwise following an identical 6-week endurance training (ET) program. Non-response was defined as any change in CRF, determined by maximal incremental exercise power output (Wmax ), within the typical error of measurement (±3.96%). Participants classified as non-responders after the ET intervention completed a successive 6-week ET period including 2 additional exercise sessions per week. Maximal oxygen consumption (VO2max ), haematology and muscle biopsies were assessed prior to and after each ET period. After the first ET period, Wmax increased (P < 0.05) in groups '2', '3', '4' and '5', but not '1' . In groups '1', '2', '3', '4' and '5', 69%, 40%, 29%, 0% and 0% of individuals, respectively, were non-responders. After the second ET period, non-response was eliminated in all individuals. The change in VO2max with exercise training independently determined Wmax response (partial correlation coefficient (rpartial ≥0.74, P < 0.001). In turn, total hemoglobin mass was the strongest independent determinant of VO2max (rpartial = 0.49, P < 0.001). In conclusion, individual CRF non-response to exercise training is abolished by increasing the dose of exercise and primarily a function of haematological adaptations in oxygen-carrying capacity. This article is protected by copyright. All rights reserved.
Montero, David