Power output at the moderate-to-heavy intensity transition decreases in a non-linear fashion during prolonged exercise
Gabriele Gallo, Emanuela Luisa Faelli, Piero Ruggeri, Luca Filipas, Roberto Codella, Daniel J. Plews, Ed Maunder
Abstract
Abstract Purpose The aims of this study were to: (i) describe the time course of the decrease in power output at the moderate-to-heavy intensity transition during prolonged exercise; (ii) investigate the association between durability of the moderate-to-heavy intensity transition and exercise capacity; and (iii) explore physiological correlates of durability of the moderate-to-heavy intensity transition. Methods Twelve trained cyclists (age: 40 ± 8 y, $$\dot{\text{V}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mover> <mml:mtext>V</mml:mtext> <mml:mo>˙</mml:mo> </mml:mover> </mml:math> O 2 peak: 52.3 ± 5.2 mL·min −1 ·kg −1 ) performed an exhaustive cycling protocol involving alternating incremental exercise tests to determine power output at the moderate-to-heavy intensity transition via the first ventilatory threshold (VT 1 ), and 30-min bouts at 90% of the power output at the previously estimated VT 1 in the rested state. The individual time course of VT 1 was modelled using linear and second-order polynomial functions, and time to a 5% decrease in VT 1 (Δ5%VT 1 ) was estimated using the best-fitting model. Results Power output at VT 1 decreased according to a second-order polynomial function in 11 of 12 participants. Time-to-task failure (234 ± 66 min) was correlated with Δ5%VT 1 (139 ± 78 min, r s = 0.676, p = 0.016), and these were strongly correlated with absolute and relative rates of fat oxidation at specific exercise intensities measured during the incremental test performed in the rested state. Conclusions These data: (i) identify a non-linear time course of decreases in the moderate-to-heavy intensity transition during prolonged exercise; (ii) support the importance of durability of the moderate-to-heavy intensity transition in prolonged exercise capacity; and (iii) suggest durability of the moderate-to-heavy intensity transition is related to fat oxidation rates.