Author(s): STEWART, L., COATES, K., GALLOWAY, C., DAWKINS, T., STEVENS, P., LIM, J., WILLIAMS, C., MOTTUS, A., SHAVE, R., EVES, N., Institution: UNIVERSITY OF BRITISH COLUMBIA - OKANAGAN, Country: CANADA, Abstract-ID: 2635

INTRODUCTION:
Most evidence describing endurance-training adaptations derives from cross-sectional comparisons (athletes vs. non-athletes) or short-term interventions (i.e. 4-12wk). Consequently, longitudinal responses to prolonged ultra-endurance training in exercise-naïve individuals remain poorly characterized, and it is unclear whether training elicits primarily improvements in maximal aerobic power (VO₂max) and/or submaximal metabolic adaptations that shift thresholds and enhance exercise sustainability. Therefore, we aimed to quantify changes in VO₂max and key determinants of endurance performance following 12 months of ultra-endurance training in exercise-naïve adults.
METHODS:
Forty-one exercise-naïve adults (21F:20M) enrolled in a 12-month individualized, progressive ultra-endurance training program; 31 participants completed testing at baseline (BL), 3, 6, and 12 months. Weekly training volume progressed from ~3h to ~17 h·wk⁻¹. VO₂max was determined during a graded cycling exercise test, from which power at the second ventilatory threshold (VT2) was also derived. Endurance performance was assessed as time-to-exhaustion during a constant-load cycling test (CLT) performed at 115% of BL VT2 power. Exercise sustainability was evaluated using time completed in the CLT (capped at 1800 s), blood lactate, heart rate (HR), and ratings of perceived exertion (RPE) sampled at 10-min intervals and at end-of-test.
RESULTS:
VO₂max increased from 38.4±7.3 at BL to 40.5±6.1 and 41.9±6.1 mL·kg⁻¹·min⁻¹ at 3 and 6 months, respectively (both p<0.001), no further improvement occurred at 12 months (42.2±7.0 mL·kg⁻¹·min⁻¹, p>0.05, +11±11% vs. BL). Time-to-exhaustion increased from 1210±539 s at BL to 1629±317 and 1759±150 s at 3 and 6 months, respectively (both p<0.026), with no further improvement at 12 months (1730±271 s, p>0.05, +76±77% vs. BL). Power at VT2 increased from 157±35 W at baseline to 190±43 W at 12 months (p<0.001, 22±18%), and peak blood lactate during the CLT decreased from 9.0±2.5 mmol·L⁻¹ at baseline to 4.6±1.9 at 12 months (p<0.001, -46±26%), accompanied by reductions in HRmax (180±14 to 164±15 bpm, p<0.001, -9±7%,) and RPE (7.2±1.6 to 4.7±1.5, p<0.001, -29±35%).
CONCLUSION:
Twelve months of ultra endurance training in exercise-naïve adults produced modest–albeit meaningful–improvements in VO₂max (+11%), whereas endurance performance increased markedly (+76%). The ~7-fold larger relative improvement in performance compared with VO₂max demonstrates that long-term endurance adaptations in exercise-naïve individuals training for an ultra-endurance event manifest predominantly as changes in the ability to sustain higher power outputs for longer, rather than marked increases in maximal O2 uptake. As most ultra-endurance training is done predominantly in training zones below VT2, it is understandable why there is a limited effect on VO2max despite substantial improvements in exercise tolerance, which are likely through specific cardiovascular and metabolic adaptations.