Knee Extensor Power Predicts Six-Minute Walk Test Performance In Transfemoral Amputees

Abstract

PURPOSE: To quantify the relationship between intact limb quadriceps strength in transfemoral amputees and six-minute walk test (6MWT) performance. METHODS: 11 participants with unilateral transfemoral amputations (4F/7M, 46.21 ± 12.68 years old, 28.24 ± 20.57 years following amputation) completed isokinetic (120 degrees/s) and isometric quadriceps strength testing on the intact limb and the 6MWT on a treadmill with a flowmeter to measure oxygen uptake (VO2). Bivariate Pearson correlations were calculated to identify the relationship between strength and 6MWT performance. Strength measures included mass-normalized peak torque, average torque, and average power. Walking measures included total distance traveled during the 6MWT, average VO2, and total VO2. VO2 measures were normalized to distance traveled and mass. Significant correlations (P < .05) were retained for a multiple regression analysis to identify the proportion of variance explained by the distance traveled (model 1) and the total VO2 (model 2). RESULTS: Peak isokinetic knee extensor torque was correlated with total VO2 (r = -.60, P = .05) and distance traveled (r = .84, P = .001). Average isokinetic knee extensor torque was correlated with total VO2 (r = -.61, P = .046) and distance traveled (r = .85, P = .001). Average knee extensor power was correlated with total VO2 (r = -.67, P = .026) and distance traveled (r = .88, P < 0.001). Peak isometric knee extensor torque was correlated with distance traveled (r = .69, P = .019). Average knee extensor power had the strongest correlation with both distance and total VO2 and was significantly correlated with all other strength variables, therefore was the only variable entered into the linear regression models. Average power explained 77.2% of the variance in distance traveled during the 6MWT (P < .001). In the second model, average power explained 44.2% of the variance in total VO2 during the 6MWT (P = .026). CONCLUSIONS: Knee extensor strength was correlated with performance on the 6MWT in individuals with unilateral transfemoral amputation. The strongest relationship was between quadriceps power and distance traveled, which suggests that developing quadriceps power in the intact limb following amputation may be an important factor to reduce metabolic cost of walking and support a return to an active lifestyle.