The use of the 6-min walk test as a proxy for the assessment of energy expenditure during gait in individuals with lower-limb amputation.

The objective of this study was to determine, and compare, the utility of the 6-min walk test (6 MWT) and self-selected walking speed over 15 m as proxies for the assessment of energy expenditure during gait in individuals with lower-limb amputation. Patients with unilateral, transfemoral amputation (n=6) and patients with unilateral, transtibial amputation (n=10) from community-based support groups participated in this study. Age-matched and body mass index-matched able-bodied controls (n=28) from a sample of convenience also participated. The main outcome measures were as follows: (a) distance, heart rate, oxygen consumption and oxygen cost during the 6 MWT and (b) self-selected walking speed over 15 m. Oxygen cost did not correlate significantly with self-selected walking speed over 15 m (ρ=-0.329) or average walking speed during the 6 MWT (ρ=-0.350). Significant correlations were not present between oxygen cost and the walking speed during the 6 MWT (range, ∣ρ∣: 0.210-0.531), although walking speeds at particular times of the 6 MWT demonstrated stronger correlations than others. Walking speed in the third min of walking during the 6 MWT recorded the strongest correlation with peak oxygen cost (ρ=-0.531). The 6 MWT is a submaximal measure in persons with lower-limb amputation. Self-selected walking speed over 15 m was not an appropriate proxy for the assessment of the energy cost of gait. Individuals with a lower-limb amputation require approximately 3 min of continuous walking to re-establish homoeostasis in heart rate, oxygen consumption and oxygen cost. The nonsignificant correlation between walking speeds during the 6 MWT and oxygen cost suggest that the 6 MWT can provide an indication of oxygen cost, but caution should be exercised when using it as a sole proxy for the measurement of oxygen cost in individuals with lower-limb amputation.