New Approaches to Marking Stages of Incremental Physical Work by Example of Cardiopulmonary Exercise Testing

Abstract

The present study aims to divide physiological stages of involving physiological compensatory reactions in organs and systems which provide transport and consumption of O2 during incremental physical exercise in healthy adults. Twenty seven untrained healthy volunteers, 19 men, mean age 25.0 ± 8.7 (18-28 years), BMI (body mass index) 26 ±2.8 (19.0-27.3 kg/height, m 2 ) and 18 triathletes, 10 men, mean age 22.3 ± 3.2 (17-25 years), BMI 21.4 ± 2.1 (19.8-23.4 kg/height, m 2 ) were evaluated during progressive treadmill exercise test. CPET (cardiopulmonary exercise testing) was performed on treadmill with gas exchange system Oxycon Pro (Jaeger, Germany). Individual incremental exercise test protocol (ramp protocol) was created for every participant. All persons reached peak exercise in 12-15 minutes. Everybody was instructed to perform maximal exercise. Maximal exercise has been defined by a plateau of VO2 (absence of increase VO2 during incremental work rate), achievement RER 1.2 or maximal predicted HR (heart rate). The cubital venous catheter was installed in all subjects before exercise test. Blood samples were taken at baseline and at 1-minute intervals during test. PH, lactate and HCO3 - concentration were estimated using analyzer i-STAT, cartridge CG4 (Abbot, USA). Physiological stages of involving compensatory reactions were determined by changes in pH, lactate and HCO3 - levels in correlation with dynamics of VO2 (oxygen uptake), VCO2 (carbon dioxide output), VE (minute ventilation), VE/VCO2 (ventilatory equivalent of carbon dioxide), RER (respiratory exchange ratio). RCP (respiratory compensation point) was determined, when ventilation dramatically increase relative to carbon dioxide output. Maximal work rate of athletes was reliably higher than of untrained healthy volunteers due to high level of training. Through first 3-5 min lactate concentration in blood was 2.1 ± 0.2 (1.9-2.5) Mm/L. It starts to increase when intensity of physical exercise reaches 12%-30% VO2 peak and comes up to 12 ± 3.2 Mm/L (8-19 Mm/L) on exercise peak. Significant inflection of lactate concentration curve can be fixed on this stage and after this lactate concentration increases gradually. pH and HCO3 - values were in normal limits at baseline: pH 7.32 ± 0.05, HCO3 - 27.3 ± 2.1 Mm/L. pH does not change significantly till the intensity of exercise ≥ 45% of VO2 peak and after this begins to diminish, that marks start of metabolic acidosis development. In all examined persons, this phenomenon appears significantly later than the increase of lactate concentration. Plateau of VO2 appears at exercise intensity 93 ± 2.5% VO2 peak. Entry of exercise in stage of plateau means that either cardiovascular and pulmonary systems, provide delivery of O2 as utilization O2 in muscles achieve its maximal capacities and increase of aerobic energy production is impossible further. Thus, we have marked four physiological stages during incremental physical exercise: lactate threshold, pH-threshold, respiratory compensation point and aerobic limit.