External work is deficient in both limbs of patients with unilateral PAD

Abstract

External work was utilized to measure differences between the unaffected and the affected limb in patients with unilateral peripheral arterial disease compared to healthy controls. Patients with unilateral peripheral arterial disease have shown deficits in peak joint powers during walking in the unaffected and affected legs. However, no research has detailed the amount of work that is being performed by each leg compared to healthy controls even though such an analysis would provide valuable information on the energy output from the affected and the unaffected legs. Two hypotheses were tested: (a) the unaffected and affected leg would perform less work than healthy controls in a pain-free state, and (b) the onset of symptomatic claudication pain would result in further changes in the external work. Results showed that during a pain-free state, both the unaffected and affected legs perform less work than the healthy controls. After onset of claudication pain, the work output by the affected limb becomes further decreased while the unaffected limb experiences changes in negative external work. These findings combined with recent evidence of decreased peak powers in both legs in unilateral peripheral arterial disease patients reflects altered pathomechanics in both limbs compared to healthy controls.

Figure 1

Mean ensemble curves for external work (integral of power-time plot). Plots have been normalized to 100% stance phase. Power is normalized to body mass. Vertical dashed lines denote average timing for end of initial double support and beginning of terminal double support. In the pain state, the unaffected leg is doing more work throughout the stance phase as the affected leg takes on less work. PWDS1, positive work initial double support; NWDS1, negative work initial double support; PWSS, positive work single support; NWSS, negative work single support; PWDS2, positive work terminal double support; NWDS2, negative work terminal double support; TotPW, total positive work through entire stance; TotNW, total negative work through entire stance. Initial double support corresponds to early stance loading for lead leg. Terminal double support corresponds to push-off for trailing leg.

Figure 2

Average external work by the peripheral arterial disease patients’ unaffected and affected legs during pain-free and pain walking as well as the healthy controls’ legs normalized to body mass. Primary differences occurred with the positive work output in terminal double support for both the unaffected and affected limbs. The onset of pain led to further decreased work output for the affected limb. UL, unaffected limb; AL, affected limb; PWDS1, positive work initial double support; NWDS1, negative work initial double support; PWSS, positive work single support; NWSS, negative work single support; PWDS2, positive work terminal double support; NWDS2, negative work terminal double support; TotPW, total positive work through entire stance; TotNW, total negative work through entire stance. Initial double support corresponds to early stance loading. Terminal double support corresponds to push-off. * Significant vs healthy control, p<0.05 †Significant pain-free vs pain state, p<0.05