Do functional walk tests reflect cardiorespiratory fitness in sub-acute stroke?

Background and purpose: The Six-Minute Walk Test (6MWT) has been employed as a measure of functional capacity, but its relationship to cardiorespiratory fitness in stroke is not well established. Gait speed measured over short distances is commonly used as an index of walking competency following stroke. We evaluated the relationship between the 6MWT, aerobic fitness (VO(2)peak) and walking competency in sub-acute stroke. Methods: Thirty-six individuals (mean age +/- SD, 64.6 +/- 14.4 years; time post-stroke 16.2 +/- 13.3 days) were evaluated using the 6MWT (distance, speed, heart rate), a maximal exercise test (VO2peak, heart rate, exercise test duration), and walking competency using a five meter walk (speed, symmetry ratio). Correlation analyses were used to examine the relationships between these outcomes. Results: There was a strong correlation between the 6MWT and five meter walk velocity for preferred (r = 0.79) and fast (r = 0.82) speed (p < 0.001). On average, the 6MWT speed was faster than the preferred gait speed (94.9 cm/ s vs. 83.8 cm/ s, p = 0.003), but slower than the fast-paced walk (115.1 cm/ s, p < 0.001). There was significant though more moderate association between 6MWT distance and VO(2)peak (r = 0.56, p < 0.001) and exercise test duration (r = 0.60, p < 0.001). Conclusion: The speed selected during the 6MWT was strongly related to the velocities selected during the five meter walk distance (intermediate to the selected preferred and fast speeds). Although the 6MWT may be challenging to the cardiorespiratory system, it appears to be more strongly influenced by potential limits to walking speed rather than cardiorespiratory capacity. As a result, this test is not, by itself, an adequate measure of aerobic fitness early after stroke.