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Oxygen uptake during Nordic walking training in patients rehabilitated after coronary events.

BACKGROUND
Nordic walking (NW) is an effective form of endurance training in cardiac rehabilitation (CR). The key parameter for the safety and effectiveness of the training is its intensity. Training intensity may be directly measured by the volume of oxygen consumption (VO₂), and indirectly by chronotropic cardiac response to exercise. No data have been published on the rates of VO₂ during NW in field conditions among patients rehabilitated after coronary events.


AIM
To assess the intensity of NW training in field conditions by measuring VO₂, energy expenditure (EE), and heart rate (HR) in comparison with a treadmill cardiopulmonary exercise test (CPET) in a group of patients rehabilitated after coronary events.


METHODS
Thirteen men after percutaneous coronary intervention due to an acute coronary syndrome (STEMI, NSTEMI, or UA), aged 53.2 ± 8.2 years, were evaluated and recruited for comprehensive CR at 30.3 ± 15.7 days after the incident. Left ventricular ejection fraction was evaluated and treadmill exercise test (ExT) using an individualised ramp protocol was performed during initial functional assessment. Following risk stratification, patients began training at 50% of HR reserve (HRR). Participants at low and moderate risk qualified for field NW training in the second week of CR. Treadmill CPET using a ramp protocol was performed after the patients had mastered the technique of walking with poles. Next day, HR, parameters of ventilation, and respiratory gas concentrations were measured during NW using a portable spiroergometry system.


RESULTS
Exercise tolerance estimated during initial ExT was 9.1 ± 2.5 MET. Peak VO2 was 27.5 ± 5.4 mL/min/kg during CPET vs. 26.2 ± 7.7 mL/min/kg during NW (p < 0.447). Mean VO₂ during NW was 17.5 ± 4.5 mL/min/kg, which amounted to 59.4 ± 18.6% of VO₂ reserve in CPET. Mean HR during NW was 104.8 ± 9.8 bpm, amounting to 63.7 ± 28.7% of HRR, and peak HR was 128.4 ± 13.7 bpm vs. 131.1 ± 18.0 bpm during CPET (p < 0.628). EE during 24.7 ± 9.7 min of NW was 210.7 ± 149.0 kcal (8.1 ± 2.7 kcal/min).


CONCLUSIONS
The intensity of NW training in field conditions in patients after coronary events was 59% of VO₂ reserve, and its peak instantaneous intensity reached values obtained during CPET on a treadmill. EE during NW in the study group was 8.1 kcal/min. Chronotropic response during NW was 64% of HRR, and its instantaneous increase reached the maximum HR obtained during CPET.