Revisiting the mechanics and energetics of walking in individuals with chronic hemiparesis following stroke: from individual limbs to lower limb joints

Dominic James Farris, Austin Hampton, Michael D Lewek, Gregory S Sawicki, Dominic James Farris, Austin Hampton, Michael D Lewek, Gregory S Sawicki

Abstract

Background: Previous reports of the mechanics and energetics of post-stroke hemiparetic walking have either not combined estimates of mechanical and metabolic energy or computed external mechanical work based on the limited combined limbs method. Here we present a comparison of the mechanics and energetics of hemiparetic and unimpaired walking at a matched speed.

Methods: Mechanical work done on the body centre of mass (COM) was computed by the individual limbs method and work done at individual leg joints was computed with an inverse dynamics analysis. Both estimates were converted to average powers and related to simultaneous estimates of net metabolic power, determined via indirect calorimetry. Efficiency of positive work was calculated as the ratio of average positive mechanical power [Formula: see text] to net metabolic power.

Results: Total [Formula: see text] was 20% greater for the hemiparetic group (H) than for the unimpaired control group (C) (0.49 vs. 0.41 W · kg(-1)). The greater [Formula: see text] was partly attributed to the paretic limb of hemiparetic walkers not providing appropriately timed push-off [Formula: see text] in the step-to-step transition. This led to compensatory non-paretic limb hip and knee [Formula: see text] which resulted in greater total mechanical work. Efficiency of positive work was not different between H and C.

Conclusions: Increased work, not decreased efficiency, explains the greater metabolic cost of hemiparetic walking post-stroke. Our results highlighted the need to target improving paretic ankle push-off via therapy or assistive technology in order to reduce the metabolic cost of hemiparetic walking.

Figures

Figure 1
Figure 1
Group mean instantaneous and average ILM powers. (A) Group mean (± s.d.) individual limbs method (ILM) instantaneous powers for unimpaired controls, normalised to 101 points over a stride starting from left foot heel strike. (B) Group mean (± s.d.) ILM instantaneous powers for hemiparetic walkers normalised to 101 points over a stride starting from paretic limb heel strike. (C) Group mean (± s.e.m.) positive and negative average limb powers during each of the transition-based phases of the gait cycle for unimpaired controls. (D) Group mean (± s.e.m.) positive and negative average limb powers during each of the transition-based phases of the gait cycle for hemiparetic walkers. For (C) and (D) the bars between each of the vertical dotted lines (indicating step-to-step transition events) represent average positive or negative power generated by each limb over the period between those transition events. ST - start of step-to-step transition; ET - end of step-to-step-transition; RTO - Right toe-off; RHS - right heel-strike; LTO - Left toe-off; PTO - paretic toe-off; NTO - non-paretic toe-off; NHS - non-paretic heel-strike. T1 - first transition phase, T2 - second transition phase. *Indicates significant difference between that average power value and the corresponding average power in the opposite panel, also marked with a *(i.e. a difference between unimpaired controls and hemiparetic groups).
Figure 2
Figure 2
Group mean instantaneous and average ankle joint powers. (A) Group mean (± s.d.) Ankle instantaneous powers for unimpaired controls, normalised to 101 points over a stride starting from left foot heel strike. (B) Group mean (± s.d.) Ankle instantaneous powers for hemiparetic walkers normalised to 101 points over a stride starting from paretic limb heel strike. (C) Group mean (± s.e.m.) positive and negative average ankle powers during each of the transition-based phases of the gait cycle for unimpaired controls. (D) Group mean (± s.e.m.) positive and negative average ankle powers during each of the transition-based phases of the gait cycle for hemiparetic walkers. For (C) and (D) the bars between each of the vertical dotted lines (indicating step-to-step transition events) represent average positive or negative power generated by each limb over the period between those transition events. ST - start of step-to-step transition; ET - end of step-to-step-transition; RTO - Right toe-off; RHS - right heel-strike; LTO - Left toe-off; PTO - paretic toe-off; NTO - non-paretic toe-off; NHS - non-paretic heel-strike. *Indicates significant difference between that average power value and the corresponding average power in the opposite panel, also marked with a *(i.e. a difference between unimpaired controls and hemiparetic groups); + indicates significant difference between that average power value and the equivalent average power in the same panel (i.e. a difference between paretic and non-paretic ankles).
Figure 3
Figure 3
Group mean instantaneous and average knee joint powers. (A) Group mean (± s.d.) Knee instantaneous powers for unimpaired controls, normalised to 101 points over a stride starting from left foot heel strike. (B) Group mean (± s.d.) knee instantaneous powers for hemiparetic walkers normalised to 101 points over a stride starting from paretic limb heel strike. (C) Group mean (± s.e.m.) positive and negative average knee powers during each of the transition-based phases of the gait cycle for unimpaired controls. (D) Group mean (± s.e.m.) positive and negative average knee powers during each of the transition-based phases of the gait cycle for hemiparetic walkers. For (C) and (D) the bars between each of the vertical dotted lines (indicating step-to-step transition events) represent average positive or negative power generated by each limb over the period between those transition events. ST - start of step-to-step transition; ET - end of step-to-step-transition; RTO - Right toe-off; RHS - right heel-strike; LTO - Left toe-off; PTO - paretic toe-off; NTO - non-paretic toe-off; NHS - non-paretic heel-strike. *Indicates significant difference between that average power value and the corresponding average power in the opposite panel, also marked with a *(i.e. a difference between unimpaired controls and hemiparetic groups); + indicates significant difference between that average power value and the equivalent average power in the same panel (i.e. a difference between paretic and non-paretic knees).
Figure 4
Figure 4
Group mean instantaneous and average hip joint powers. (A) Group mean (± s.d.) Hip instantaneous powers for unimpaired controls, normalised to 101 points over a stride starting from left foot heel strike. (B) Group mean (± s.d.) hip instantaneous powers for hemiparetic walkers normalised to 101 points over a stride starting from paretic limb heel strike. (C) Group mean (± s.e.m.) positive and negative average hip powers during each of the transition-based phases of the gait cycle for unimpaired controls. (D) Group mean (± s.e.m.) positive and negative average hip powers during each of the transition-based phases of the gait cycle for hemiparetic walkers. For (C) and (D) the bars between each of the vertical dotted lines (indicating step-to-step transition events) represent average positive or negative power generated by each limb over the period between those transition events. ST - start of step-to-step transition; ET - end of step-to-step-transition; RTO - Right toe-off; RHS - right heel-strike; LTO - Left toe-off; PTO - paretic toe-off; NTO - non-paretic toe-off; NHS - non-paretic heel-strike. *Indicates significant difference between that average power value and the corresponding average power in the opposite panel, also marked with a *(i.e. a difference between unimpaired controls and hemiparetic groups); + indicates significant difference between that average power value and the equivalent average power in the same panel (i.e. a difference between paretic and non-paretic hips).
Figure 5
Figure 5
Group mean distributions ofP¯+(solid outline) andP¯−(dashed outline) as determined by the JPM. Top and bottom pies for each represent the distribution when both limbs are summed. The distributions of P¯+ and P¯− within each limb are then represented in the two smaller pies linked to each larger pie. The total area of each pie represents total work of that pie relative to all other pies. *denotes a statistically significant difference from unimpaired controls (P < 0.05).

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