Author(s): OMALLEY, B., ROBERGS, R.A., MCNULTY, C.R., Institution: UNIVERSITY OF THE SUNSHINE COAST, Country: AUSTRALIA, Abstract-ID: 1730

INTRODUCTION:
During maximal ramp-incremental exercise (RIE), whole-body oxygen uptake (VO2) may increase disproportionately near exhaustion, complicating the determination of maximal oxygen consumption (VO2max) during athlete performance testing. These increases may reflect skeletal muscle VO2 demand but may also include substantial contributions from the respiratory and postural musculature, thereby increasing the VO2 cost of ventilation (VO2VENT). Such variability complicates traditional confirmation of VO2max based on the presence of a VO2 plateau. Consequently, the absence of a VO2 plateau may not indicate a failure to reach physiological maximum but instead reflect intensity-dependent shifts in the contributors to whole-body VO2. While VO2VENT has been quantified in recreational populations, its influence on VO2max determination remains poorly defined in highly trained endurance athletes. Quantifying this contribution is therefore critical for isolating skeletal muscle VO2 and improving interpretation of VO2max in applied testing.
METHODS:
Eight highly trained male endurance athletes (Age, 35 +/- 7 yrs; VO2max 5.75 +/- 0.620 L min-1) performed a maximal RIE cycling test. Breath-by-breath pulmonary gas-exchange was measured using a calibrated fast-response turbine flow transducer (Hans Rudolph-430) and rapid response electronic gas analyzers (AEI Technologies, Model S-3 A and Model CD-3H). VO2max was defined as the highest 15-breath average. VO2VENT was measured during separate voluntary hyperpnoea trials at rest (50-95% of maximal inspired ventilation; MaxVI) with hypercapnic gas (FICO2 = 3.7%; FIO2 = 21%; balance N2) used to prevent hypocapnia. Individual VI-VO2 relationships were modelled and extrapolated to estimate VO2VENT at 100% MaxVI, then applied to RIE data. Whole-body VO2 was corrected for VO2VENT (VO2VCORR), and linear slopes of the final 30 s of exercise were compared between measured VO2 and VO2VCORR using paired t-tests (p<0.05).
RESULTS:
At VO2max, VO2VENT accounted for 11.1% +/- 2.1% (range 8.4-13.9%) of whole-body VO2. Individual VI-VO2 regressions were highly linear (R2 = 0.90 +/- 0.10). Correcting for VO2VENT significantly decreased the final 30 s VO2 slope (0.320 +/- 0.178 vs. 0.171 +/- 0.135 mL min-1 W-1; p < 0.0001). Participants exhibited increased breathing frequency and reduced tidal volume prior to and near exhaustion.
CONCLUSION:
Respiratory work imposes a substantial metabolic load in highly trained endurance athletes and significantly increases VO2 near exhaustion. Accounting for VO2VENT refines estimates of skeletal muscle VO2 demand, improves VO2max accuracy and interpretation, and enhances athlete performance test interpretation. This work establishes VO2VENT as a measurable and modifiable contributor to VO2max, warranting targeted investigation of respiratory training strategies to improve ventilatory efficiency and endurance performance.