Metamax 2

As an assessment of the participants’ general physical activity, whole body V̇o_2max was determined using a Metamax II gas analyzer (Cortex Biophysik, Leipzig, Germany). An incremental treadmill protocol was applied (Woodway PPS Med, Woodway USA, Waukesha, WI) starting with 5% inclination, and where speed and/or inclination was increased each minute until exhaustion. V̇o_2max was considered achieved when two or more of the following criteria were met: an asymptote in oxygen uptake development despite increases in workload, respiratory exchange ratio of 1.10, and/or being within 5 beats·min⁻¹ of maximal heart rate if this was known (16 (link)).

During all tests, respiratory gases were constantly collected and analyzed via the Metalyzer or MetaMax II metabolic test system (Cortex Biophysik, Leipzig, Germany) using the same system for all trials of a given subject. Subjects breathed through a Hans-Rudolph-facemask that was selected prior to the first exhaustive graded exercise test and remained the same during the course of the study. According to the manufacturer's instructions, a calibration was performed before each use.

Participants walked at 4.5 km·h⁻¹ at 5% inclination for 5 min to warm up before the treadmill (Woodway, Waukesha, WI) speed and/or inclination was gradually increased every 3 min to reach V̇o_2max (31 (link)). Pulmonary gas exchange variables were obtained every 10 s (Metamax II, Cortex Biophysik GmbH, Leipzig, Germany). The highest 30-s average of V̇o₂ was reported as V̇o_2max. V̇o_2max was accepted when no further increase in V̇o₂ was observed despite increased speed/inclination and a respiratory exchange ratio ≥ 1.05 was present.

Pulmonary VO_2max was measured using a Metamax II portable gas analyzer (Cortex Biophysik) on a treadmill calibrated for speed and inclination (Gymsport TX200). Simultaneously, heart rate was continually registered during the test using Polar RS100 (Polar Electro). In addition to determining VO_2max and HR_max, performing an incremental cardiorespiratory exercise test is recommended to maximize patient safety and ensure exercise tolerance [35 (link)] before commencing a training program. Following a 6-min warm-up period at 4.0 km/h at 5% treadmill inclination, the workload was increased in increments of 1.0 km/h or 1% every minute until exhaustion. This implies that subjects with a low VO_2max typically performed the test walking, while subjects with a high VO_2max were running during the final minutes of the test. Participants received verbal encouragement and feedback from the tester throughout the test. A respiratory exchange ratio ≥1.05, in combination with a plateau in VO₂ despite increased work rate, was used as the criterion for reaching VO_2max [36 (link)]. If the criterion for achieving VO_2max was not reached, a retest was scheduled 3 days later. If the criterion was still not met, a VO_2peak was reported. VO_2max was calculated as the mean of the 3 highest consecutive 10-second measurements. The highest heart rate measured during the last minute of the test was used as HR_max.