Effect of endurance training on the fractional utilization of VO2max in untrained subjects

Abstract

Introduction: Within endurance-trained subjects, short term endurance training is assumed to have minor impact on fractional utilisation of maximal oxygen consumption (%VO2max), and systematic endurance training over years is required (Basset & Howley, 2000; Rusko, 1987). The effect of endurance training on %VO2max within untrained individuals remains unclear. The potential differences in improvements between a group of untrained individuals and a control group remains unexplored. Therefore, this study aimed to examine the impact of endurance training on %VO2max by comparing a group of untrained subjects and a control group consisting of well-trained cyclists.

Methods: Seven endurance trained cyclists (≥ 3 years of systematic endurance training) were recruited to a control group (CON) and eight untrained subjects (≤ 1 session/week of endurance training the last year) were recruited to an intervention group (INT). Both groups performed pre-test prior to the intervention, and post-test after eight weeks. In addition, INT performed midway-testing after four weeks. A 30-min time trial (TT) was performed to determine endurance performance. %VO2max was measured as the average oxygen consumption during the 30-min TT (VO2@30TT) as percentage of VO2max. CON did their regular training for eight weeks, without manipulation from the study. The participants within INT performed supervised endurance training 3x/week for seven weeks.

Results: Within CON, VO2@30TT tended to increase (p=0.06), but TT performance (PO@30TT) and %VO2max remained unchanged (all p>0.2). There were no changes in any variables assessed during the maximal and submaximal exercise (all p>0.3). Within INT, blood lactate concentration and heart rate at submaximal exercise ([La-]@submax and HR@submax) decreased from pre-test to post-test (-32.7 ± 7.9 % and -4.4 ± 5.3%, respectively, all p<0.09). VO2max (ml∙min-1) increased from pre-test to midway-test (8.3 ± 7.1%, p=0.01), and pre-test to post-test (13 ± 3.5%, p=0.01). PO@30TT improved and VO2@30TT increased during the intervention (8.7 ± 6.3% and 9.6 ± 5.1%, respectively, all p=0.01). Yet, %VO2max remained unchanged at all test points during the intervention (all tests p>0.3).

Conclusion: This study demonstrated that seven weeks of endurance training did not improve %VO2max within untrained subjects, although TT-performance did show an improvement, due to an overall increase in VO2max. The well-trained cyclists did not improve %VO2max and TT-performance during the intervention, because of their high-performance level and high initial VO2max.