Cardiorespiratory Exercise Test Protocol

To determine exercise workload for the PSWT, data from the cardiorespiratory exercise test were used. All exercise intensity domains were determined by the same respiratory physiologist with experience in the area. The protocol was performed on a motorized treadmill (Centurion, model 200, Micromed, Brazil) and consisted of three 5-min stages at workloads equivalent to (1) 80% of ventilatory anaerobic threshold (VAT), (2) VAT, and (3) 40% of the difference between VAT and $\dot{\text{V}}{\text{O}}_{2\text{peak}}$ (40%Δ). These stages represented moderate, heavy and very heavy domains [25 (link)] and corresponded to 46±8%, 57±10% and 87±8% of $\dot{\text{V}}{\text{O}}_{2\text{peak}}$ . Participants then completed a final stage (severe domain) to exhaustion at a running speed equivalent to the maximum achieved during the cardiorespiratory exercise test (Peak). Ventilatory and gas exchange measurements were recorded continuously throughout using a breath-by-breath system (MetaLyzer 3B, Cortex, Germany), with the spirometer mask placed over the cloth facemask.
To determine the effect of the mask on pattern of change in operating lung volume, we evaluated end-expiratory volume to functional vital capacity ratio (EELV/FVC). Inspiratory capacity was determined at rest and at the end of each exercise stage during the PSWT. Ventilatory constraint was evaluated as the difference between inspiratory capacity at rest and at each exercise workload [26 (link)]. Ventilatory efficiency was determined using the ventilatory equivalent for carbon dioxide ( ${\dot{\text{V}}}_{\text{E}}/\dot{\text{V}}{\text{CO}}_2$ ) and end-tidal carbo dioxide pressure (PetCO₂) during each stage. Breathing pattern was evaluated during each stage using the breathing frequency to tidal volume ratio (Rf/VT) ratio [27 (link)].
Rated perceived exertion (RPE) was assessed at the end of each stage with participants pointing to a chart using the 6- to 20-point Borg scale [28 (link)]. Heart rate was monitored continuously throughout (ergo PC elite, Micromed, Brazil). A fingertip blood sample (20 μL) was collected at baseline, at the end of each stage and 4-min post-exhaustion for the subsequent analysis of lactate. Blood was homogenized in the same volume of 2% NaF, centrifuged at 2000 g for 5 min before plasma was removed and stored at -20°C until analysis. Plasma lactate was determined spectrophotometrically using an enzymatic-colorimetric method (Katal, Interteck, Brazil).