Relationship Between Step Length Asymmetry and Walking Performance in Subjects With Chronic Hemiparesis

Illustration of horizontal ground reaction force impulses. Positive values (shaded area) represent propulsion. Negative values (unshaded area) represent braking. Paretic leg is the dark curve and nonparetic leg is the light curve. Abbreviations: BW, body weight; GRF, ground reaction force; I_bn, braking impulse by the nonparetic leg is the unshaded area under the light curve; I_bp, braking impulse by the paretic leg is the unshaded area under the dark curve; I_pn, propulsive impulse by the nonparetic leg is the shaded area under the light curve; I_pp, propulsive impulse by the paretic leg is the shaded area under the dark curve.

Comparison of ground reaction forces between the paretic and nonparetic legs for individual subjects walking with differing SLR. Positive values (shaded area) represent propulsion, and the positive area under the curve is the propulsive impulse. Paretic leg is the bold curve and nonparetic leg is the light curve. (A) Subject with severe hemiparesis walking with SLR equal to 1.47 (ie, SLR >1.1) and at a speed of 0.71m/s generates decreased paretic leg propulsion (P_P). (B) Subject with mild hemiparesis walking at SLR equal to 0.98 (ie, 0.9 < SLR <1.1) at a speed of 0.75m/s generates symmetrical propulsive impulse. (C) Subject with mild hemiparesis walking with SLR equal to 0.68 (ie, SLR <0.9) and at a speed of 0.52m/s generates relatively greater paretic leg propulsion, P_P (although low in magnitude). Abbreviations: NHS, nonparetic heel strike; NTO, nonparetic toe off; PHS, paretic heel strike; PTO, paretic toe off.

Relationship between step length ratio and propulsion_paretic. The solid vertical line indicates symmetric steps (SLR=1), vertical dashed lines indicate the SLR subdivisions at SLR equal to 0.9 and SLR=1.1. Solid horizontal line indicates symmetric propulsive force generation by the paretic leg (P_P=50%), horizontal dashed lines indicate differing levels of paretic leg propulsion (10%, 30%, and 70% P_P). Step length ratio quantifies step length asymmetry and propulsion_paretic quantifies the contribution of the paretic leg to the task of propulsion. Note the decreasing paretic propulsion as SLR increases. Abbreviations: Propulsion_Paretic, paretic leg propulsion (in percent); NP, nonparetic leg; P, paretic leg.

Relationship between step length asymmetry, walking speed, and hemiparetic severity. The solid vertical line indicates symmetric steps (SLR=1), vertical dashed lines indicate the SLR subdivisions at SLR equal to 0.9 and SLR equal to 1.1. Horizontal dashed lines indicate subdivisions of walking speeds (<0.4m/s, household walkers; 0.4−0.8m/s, limited community walkers; >0.8m/s, community walkers). Note that subjects with different SLR walk at all levels of walking speeds, yet the majority of those with severe hemiparesis walk asymmetrically at SLR greater than 1.1. Also, the 4 subjects with severe hemiparesis walked at speeds greater than 0.8m/s. These subjects walked asymmetrically with SLR greater than 1.1 and generated P_P less than 25%. Contrast the 3 subjects with mild hemiparesis that walked at speeds between 0.4 and 0.8m/s. One of these walked symmetrically (0.9< SLR < 1.1) and 2 others walked asymmetrically (SLR <0.9) and generated P_P of 45% or greater. Abbreviations: NP, nonparetic leg; P, paretic leg.

Change in speed, cadence, and individual step lengths in subjects walking at different SLR (SLR > 1.1 [n=21]; 0.9< SLR < 1.1 [n=21]; SLR <0.9 [n=4]). Subjects walking with SLR greater than 1.1 increase their speed by primarily increasing their cadence, with little increase in the paretic step length. Abbreviation: Δ_FS-SS, change in speed from self-selected to fastest safe speed.