BackgroundUnderstanding the cardiorespiratory factors related to the increase in oxygen consumption () during exercise is essential for improving cardiorespiratory fitness in individuals with stroke. However, cardiorespiratory factors related to the increase in during exercise in these individuals have not been examined using multivariate analysis. This study aimed to identify cardiorespiratory factors related to the increase in during a graded exercise in terms of respiratory function, cardiac function, and the ability of skeletal muscles to extract oxygen.MethodsEighteen individuals with stroke (aged 60.1 ± 9.4 years, 67.1 ± 30.8 days poststroke) underwent a graded exercise test for the assessment of cardiorespiratory response to exercise. The increases in from rest to first threshold and that from rest to peak exercise were measured as a dependent variable. The increases in respiratory rate, tidal volume, minute ventilation, heart rate, stroke volume, cardiac output, and arterial-venous oxygen difference from rest to first threshold and those from rest to peak exercise were measured as the independent variables.ResultsFrom rest to first threshold, the increases in arterial-venous oxygen difference (β = 0.711) and cardiac output (β = 0.572) were significant independent variables for the increase in (adjusted R2 = 0.877 p < 0.001). Similarly, from rest to peak exercise, the increases in arterial-venous oxygen difference (β = 0.665) and cardiac output (β = 0.636) were significant factors related to the increase in (adjusted R2 = 0.923, p < 0.001).ConclusionOur results suggest that the ability of skeletal muscle to extract oxygen is a major cardiorespiratory factor related to the increase in during exercise testing in individuals with stroke. For improved cardiorespiratory fitness in individuals with stroke, the amount of functional muscle mass during exercise may need to be increased.

2 3 Background: Understanding the physiological limitations of the increase in oxygen 2 4 consumption (V ሶ O 2 ) during exercise is essential to improve cardiorespiratory fitness in 2 5 individuals with stroke. However, the physiological determinants of the increase in V ሶ O 2 2 6 during exercise have not been examined using multivariate analysis in individuals with 2 7stroke. This study aimed to identify the physiological determinants of the increase in 2 8 V ሶ O 2 during a graded exercise in terms of the respiratory function, cardiac function, and 2 9ability of skeletal muscles to extract oxygen. 3 0 Methods: Eighteen individuals with stroke (60.1 ± 9.4 years of age, 67.1 ± 30.8 days 3 1 poststroke) underwent a graded exercise test for the assessment of cardiorespiratory 3 2 response to exercise. The increase in V ሶ O 2 from rest to ventilatory threshold and that 3 3 from rest to peak exercise were measured as a dependent variable. The increases in 3 4respiratory rate, tidal volume, heart rate, stroke volume, and arterial-venous oxygen 3 5 difference from rest to ventilatory threshold and those from rest to peak exercise were 3 6 measured as independent variables. 7Results: From rest to ventilatory threshold, the increases in heart rate (β = 0.546) and 3 8 arterial-venous oxygen difference (β = 0.398) were significant determinants of the 3 9 increase in V ሶ O 2 (adjusted R 2 = 0.703, p < 0.001). From rest to peak exercise, the 4 0 4 increases in tidal volume (β = 0.611) and heart rate (β = 0.353) were significant 4 1 determinants of the increase in V ሶ O 2 (adjusted R 2 = 0.702, p < 0.001). 4 2 Conclusion: V ሶ O 2 is well-known to increase nearly linearly with increasing heart rate; 4 3 however, our results suggest that arterial-venous oxygen difference and tidal volume are 4 4 also significant physiological determinants of the increase in V ሶ O 2 from rest to 4 5 ventilatory threshold and that from rest to peak exercise, respectively. Our findings 4 6 could potentially contribute to the development of appropriate therapies to improve 4 7 cardiorespiratory fitness in individuals with stroke. 4 8 4 9