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

Abstract

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 (VO2peak) 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 VO2peak (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.

Figures

Figure 1

Relationship between A) 6MWT distance and VO2peak (r = 0.56, p < 0.001), and B) end heart rate from 6MWT and peak heart rate from maximal exercise test (r = 0.66, p < 0.001), in beats per minute (bpm). Dashed line represents line of identity.

Figure 2

Relationship between 6MWT speed and A) preferred gait speed (r = 0.79, p

Figure 3

A) Relationship between gait symmetry ratio at preferred pace 6MWT distance (r = -0.26, p = 0.13), and B) CMSA individual scores (open symbols) and means and standard deviations (closed symbols and error bars) and 6MWT distance. There were no differences in 6MWT speed between participants with symmetrical versus asymmetrical gait patterns (t = 1.53, p = 0.14) and between those with different CMSA leg impairment scores (F = 2.17 p = 0.11).