Polar s610 monitor

VO_2max was determined during diagonal skiing with roller skis on a treadmill (Rodby, Södertälje, Sweden; Calbet et al., 2005 (link)), starting at 11 km⋅h^-1 on a treadmill inclination of 4° and increasing the incline by 1° each minute until exhaustion. During the tests, each subject was secured with a safety harness suspended from the ceiling. For the subjects, roller skiing on the treadmill was a regular part of their training.
Respiratory variables were determined with the mixed expired gas procedure, employing an ergo-spirometry system (AMIS 2001 model C, Innovision A/S, Glamsbjerg, Denmark) equipped with an inspiratory flowmeter. The gas analyzers were calibrated with a high-precision mixture of 16.0% O₂ and 4.0% CO₂ (Air Liquide, Kungsängen, Sweden) and the flowmeter calibrated at low, medium, and high flow rates with a 3-l air syringe (Hans Rudolph, Kansas City, MO, United States). Ambient conditions were monitored with an external apparatus (Vaisala PTU 200, Vaisala OY, Helsinki, Finland). Expired O₂ and CO₂ and the inspired minute ventilation (V Ė) were monitored continuously and VO₂ values averaged during the final 30 s at each workload. Heart rate was recorded continuously by the Polar S610 monitor (Polar Electro Oy, Kempele, Finland).

Respiratory variables were monitored with the mixed expired procedure, employing an ergo-spirometry system (AMIS 2001 model C, Innovision A/S, Odense, Denmark) equipped with pneumotachograph to measure inspiratory flow. This system was calibrated with the standardized procedure described by Björklund et al. (2007 (link), 2010 (link)). VO₂, VCO₂ and the inspired minute ventilation (V_E) were monitored continuously and the average VO₂ during the final 30 s at each workload calculated.
Heart rate (HR) was followed continuously using the Polar S610 monitor (Polar Electro Oy, Kempele, Finland) in combination with the metabolic cart. During the final minute of exercise at each bout, arterial and venous blood samples (1.5 ml) were collected anaerobically into syringes (PICO 50, Radiometer, Copenhagen, Denmark) containing heparin and then analyzed immediately for hemoglobin concentration [Hb], pH, PO₂, PCO₂, oxygen saturation (SO₂) (ABL 80; Radiometer, Copenhagen, Denmark) and lactate (Biosen 5140, EKF-diagnostic GmbH, Magdeburg, Germany). The O₂ content of arterial (CaO₂) and venous (femoral: CfvO₂; subclavian: CsvO₂) blood was calculated from the SO₂ and [Hb] as follows: (1.34 × [Hb] × SO₂) + (0.003 × PO₂) (Calbet et al. 2005 (link)).