Leg extension is an important predictor of paretic leg propulsion in hemiparetic walking

Abstract

Forward propulsion is a central task of walking that depends on the generation of appropriate anterior-posterior ground reaction forces (AP GRFs). The AP impulse (i.e., time integral of the AP GRF) generated by the paretic relative to non-paretic leg is a quantitative measure of the paretic leg’s contribution to forward propulsion and is variable across hemiparetic subjects. The purpose of this study was to investigate the underlying mechanisms of propulsion generation in hemiparetic walking by identifying the biomechanical predictors of AP impulses. Three-dimensional kinematics and GRFs were recorded from 51 hemiparetic and 21 age-matched control subjects walking at similar speeds on an instrumented treadmill. Hierarchical regression models were generated for each leg to predict the AP impulse from independent biomechanical variables. Leg extension was a significant predictor and positively related to the propulsive impulse in the paretic, non-paretic and control legs. Secondarily, the hip flexor impulse was negatively related to the propulsive impulse. Also, the relationship of paretic and non-paretic ankle moments with the propulsive impulse depended on the paretic step ratio, suggesting the plantar flexor contribution to the propulsive impulse depends on leg angle. These results suggest that increasing paretic leg extension will increase propulsion. Increasing paretic leg plantar flexor output and decreasing paretic leg hip flexor output could also increase paretic leg propulsion. While increased pre-swing hip flexor output has been suggested to compensate for decreased plantar flexor output, such output may further impair propulsion by the paretic leg if it occurs too soon in the gait cycle.

Targeting Paretic Propulsion to Improve Poststroke Walking Function: A Preliminary Study

“…However, the translation of increased plantarflexor muscle activation during FES into greater forward propulsion depends largely on the paretic limb’s posterior position relative to the individual’s center of mass during the double support phase of the paretic gait cycle 16 . Unfortunately, stroke survivors often do not achieve adequate paretic hip extension during walking 7 .…”

Understanding Spatial and Temporal Gait Asymmetries in Individuals Post Stroke

“…The forward propulsion is quantified by the time integral of the positive antero-posterior GRF [67] and ensures the forward progression of the body during gait. This subtask of gait is frequently impaired in individuals post stroke [54,67,68].…”

“…The forward propulsion is quantified by the time integral of the positive antero-posterior GRF [67] and ensures the forward progression of the body during gait. This subtask of gait is frequently impaired in individuals post stroke [54,67,68]. As proposed by Olney et al [34], an impaired paretic forward propulsion during the non-paretic swing could create an early foot contact by the non-paretic side (Figure 3, link C-5) [34].…”

“…Therefore, an impaired paretic propulsion (e.g. caused by a reduced plantarflexor work [69] or moment impulse [67]), could contribute to an increase of the paretic swing duration by reducing the kinetic energy of the leg at toe-off (Figure 3, links C-2 and C-B-A) [25,69].…”

“…plantarflexor muscles and moment impulse, knee extension moment impulse, hip flexion moment impulse (negative relation), weight bearing distribution, leg extension at push off, etc. see [67,68,[70][71][72] for detailed description of parameters related to forward propulsion). As neurophysiological studies showed that a reduced weight bearing in double support phase could reduce plantarflexor muscle activity [72], this might also explain the association observed by Kim and Eng [45] between swing time asymmetry and weight-bearing asymmetry (Figure 3, link D-C-B).…”