Knee extensor power predicts six-minute walk test performance in people with transfemoral amputations

Background: Lower-limb amputees have increased metabolic costs during walking that may be mitigated by maintaining quadriceps strength and power following amputation. However, there are no current studies investigating the relationship between thigh strength and walking performance in individuals with transfemoral amputation. Objective: To quantify the relationship between intact limb quadriceps strength in transfemoral amputees and six-minute walk test (6MWT) performance. Design: Descriptive laboratory study. Setting: Laboratory. Participants: Eleven participants with unilateral transfemoral amputations from trauma or osteosarcoma (4 women/7 men, 46.21 ± 12.68 years old, 28.24 ± 20.57 years following amputation). Interventions: Strength and power testing on the intact limb followed by 6MWT with a flowmeter to measure oxygen uptake (VO₂). Main Outcome Measures: Strength included mass-normalized peak torque, average torque, and average power. 6MWT measures included total distance traveled and VO₂ normalized to distance and mass. Significant correlations (P ≤.05) were retained for a regression analysis. 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 <.001). Peak isometric knee extensor torque was correlated with distance traveled (r =.69, P =.019). Average power explained 77.2% of the variance in distance traveled during the 6MWT (P <.001) and 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 isokinetic 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.