Quark cpet

During the preliminary visit, the height of the participants, wearing only socks, was measured to the nearest 0.5 cm using a wall stadiometer, post-void nude BM with a digital scale (BX-300+, Altron Systems, Mount Pleasant, SC, USA, ±20 g), fat mass and FFM with the dual-energy X-ray absorptiometry technology (Lunar Prodigy, GE Healthcare, Chicago, IL, USA) and blood pressure and resting heart rate using a digital sphygmomanometer (Welch-Allyn 420 series, Skaneateles Falls, NY, USA) after the participants remained seated for a period of 2 min. Finally, $\dot{\mathrm{V}}$ O_2max was determined with a metabolic analyzer (Cosmed Quark CPET, Cosmed, Chicago, IL, USA) calibrated according to the manufacturer instructions using an incremental running protocol on a motorized treadmill. Participants started walking at 5 km/h with 0% grade for 1 min, with further increments of 1 km/h occurring every 1 min until the participants could not continue. The $\dot{\mathrm{V}}$ O_2max was confirmed when at least two of those criteria were reached: (1) respiratory exchange ratio ≥ 1.1, (2) theoretical maximal heart rate (220-age), (3) $\dot{\mathrm{V}}$ O₂ plateau concurrent to an increase in running speed [17 (link)].

To assess exercise tolerance and to induce post-exertional malaise in long COVID patients, we conducted an incremental ramp exercise test on a cycle ergometer with simultaneous ECG, pulmonary gas exchange/ventilation and muscle deoxygenation measurements. All exercise tests were conducted on an electronically braked cycle ergometer (Lode Excalibur Sport, Lode, Groningen, The Netherlands). The test was preceded by 2-min quiet rest on the ergometer and 4-min baseline cycling at low intensity (between 0 and 20 W depending on height, body mass and anticipated fitness). This was followed by a ramped, linear increase in work rate until task failure. The individual baseline work rates and ramp slopes were selected based on each participant’s anthropometric characteristics and physical activity levels and designed to elicit task failure within 8–12 min. Participants were instructed to maintain their cadence between 70 and 90 revolutions/min, and task failure was defined as the point at which cadence dropped <60 revolutions/min despite verbal encouragement. Capillary lactate concentrations were determined at rest prior to the onset of the test, during baseline cycling, and immediately following task failure (Lactate Pro 2 LT-1730, ARKRAY Ltd., United Kingdom). Pulmonary gas exchange and ventilation were measured on a breath-by-breath basis (Cosmed Quark CPET; Cosmed, Rome, Italy).