Sex-specific Impact Of Stroke On Peak Oxygen Utilization During A Graded Exercise Test

The effects of stroke on cardiorespiratory (CR) fitness measured as peak oxygen utilization (V̇O2 peak) between males and females while exercising are not known. The 6-minute walk test (6MWT) has been widely used to estimate CR fitness in neurotypical individuals; however, little is known about the utility of the 6MWT for predicting V̇O2 peak in the stroke population. PURPOSE: To determine (1) if stroke affects V̇O2 peak differently between sexes and (2) the relationship between V̇O2 peak and a clinical measure of walking endurance in chronic stroke survivors. METHODS: Twenty-two chronic stroke survivors (≥ 6 months post stroke, 16 females, 60 ± 14 years) and 15 neurotypical controls (10 females, 63 ± 12 years) completed a graded exercise test to measure V̇O2 peak using a recumbent cycle ergometer and a metabolic cart. After a two-minute rest, participants pedaled at a workload of 10 Watts (W) that was increased by 15 W every two minutes. The test was terminated when: (1) participants reached volitional fatigue and requested to end test; (2) V̇O2 peak plateaued; (3) participants were unable to maintain a steady cadence >40 rpm; or (4) participants showed an adverse response to exercise. Measurements of the exhaled gases were averaged in 30-second bins. The 6MWT was performed on a separate day to assess walking endurance. A two-way ANOVA was used to determine the main and interaction effects of group (stroke vs. control) and sex (female vs. male) on V̇O2 peak. Pearson correlation was made between V̇O2 peak and the 6MWT distance. RESULTS: Stroke survivors had a lower V̇O2 peak compared to controls (group, p < 0.001; 17 ± 5 vs. 26 ± 5 mL/min/kg). The difference in V̇O2 peak post stroke was greater in females vs. males (interaction, p = 0.042; stroke female 16 ± 5 vs. control female 28 ± 5 mL/min/kg, delta 12 mL/min/kg; stroke male 18 ± 7 vs. control male 22 ± 4 mL/min/kg, delta 4 mL/min/kg). V̇O2 peak was correlated with the distance covered during the 6MWT in controls (r = 0.668, p = 0.006) but not in stroke survivors (r = 0.421, p = 0.073). CONCLUSIONS: Although stroke impairs V̇O2 peak in both males and females, the level of impairment may be greater in females. Additionally, the 6MWT may not be an optimal tool to predict CR fitness in the chronic stroke population.