Polar vantage

Participants started cycling (Ergometrics 800S; Ergoline, Bitz, Germany) at 100 W for 2 min with subsequent increases of 30 W every 2 min until exhaustion. W_max was calculated as the workload of the last completed stage plus the number of seconds during the last (uncompleted) stage times 0.25 (thus equating 30 W for every 120 s cycled, the workload and duration of each stage of the test)^{23 (link)}. Participants could choose a cycling cadence between 70 and 100 rpm within the first minutes of the test and once established it was kept within ± 3 rpm. The test ended when participants stopped or when the cadence could no longer be sustained within the designated range. Ventilation and gas exchange (Oxycon Alpha plus) were recorded breath-by-breath and heart rate (HR) was recorded continuously (Polar Vantage, Polar Electro, Kempele, Finland). The metabolic cart was calibrated for volume and gas fractions according to the manufacturer’s recommendation before and after each trial, to ensure that no technical issue or drift was present during the tests. 20 µl of capillary blood were drawn from an earlobe to analyze for blood lactate concentration ([La], Biosen 5040, EKF Diagnostic, Barleben, Germany). Finally, the participants were familiarized again with the use of the SpiroTiger device.

Cardiorespiratory fitness (CRF) was measured with a graded maximal exercise test, using a Monark 829E electronically braked cycle ergometer (Monark Exercise AB, Vansbro, Sweden). Boys started out with a 50 W resistance, which was increased by another 50 W every three minutes until exhaustion. Girls started out with a 40 W resistance, increased by another 40 W every three minutes until exhaustion [30 (link)]. The recommended pedaling rate was 70 rpm and the tests were terminated if the rate fell below 40 rpm. Heart rate was measured with a Polar heart rate monitor via chest band (Polar Vantage) as well as ratings of perceived exertion at the end of each level. The test was considered maximal if at least two out of the three following criteria were met: a heart rate no more than 5% below the age-predicted maximum, calculated as (207 − (0.7 × age) ± 10 beats), a score of 19–20 on the Borg scale of perceived exertion, and the researchers’ subjective estimates of maximal effort. CRF, expressed as maximal power output with linear regression scaling, was used in final analyses with fat free mass (FFM) entered as a covariate.

All participants completed the incremental exercise test to exhaustion. An electrically braked bicycle ergometer (Lode Cordival V3, Groningen, Netherlands) was used for exercise testing. The initial workload was set at 50 W, and every 2 min, the workload was increased by 25 W until exhaustion [40 (link)]. During the maximal exercise test, respiratory gas exchange was measured breath-by-breath, with data being recorded in 10 s intervals to measure oxygen consumption (VO₂) by a gas analyzer (SpiroPro SensorMedics, Yorba Linda, CA, USA). Peak oxygen consumption (VO₂peak; L·min⁻¹) was considered the highest VO₂ rate achieved within 30 s at the end of the exercise test [40 (link)]. CRF was defined by absolute VO₂peak (L·min⁻¹), relative VO₂peak per kg of body mass (VO₂peak/_kg; mL·kg⁻¹·min⁻¹) and by VO₂peak per kg of LBM (VO₂peak/_LBM; mL·kg⁻¹·min⁻¹) [38 (link),41 (link)]. Heart rate (HR) was continuously monitored with a heart rate monitor (Polar Vantage, Polar Electro OY, Kempele, Finland).