Relationships between muscle activity and anteroposterior ground reaction forces in hemiparetic walking

Abstract

Objective: To determine relationships between muscle activity and propulsive impulse in hemiparetic walking.

Design: Cross-sectional.

Setting: Gait analysis laboratory.

Participants: Forty-nine poststroke patients with chronic hemiparesis, stratified into hemiparetic severity subgroups based on Brunnstrom stages of motor recovery, walking at their self-selected speed.

Interventions: Not applicable.

Main outcome measures: Percent of muscle activity in the paretic and nonparetic legs and net anteroposterior (AP) ground reaction force impulse (ie, the time integral of the AP ground reaction force) within 4 regions of the stance phase (first double support, first and second halves of single support, and second double support).

Results: Medial gastrocnemius and soleus muscle activity correlated positively with paretic propulsion in the second half of single support and double support across all subjects and subjects grouped by hemiparetic severity. Tibialis anterior correlated negatively with paretic propulsion during preswing across all subjects and for subjects with moderate and severe hemiparesis. Rectus femoris activity also correlated negatively with preswing propulsion for the severe group. Uniarticular knee extensor activity correlated only with increased paretic braking in the first double-support phase for the severe hemiparesis group. Nonparetic leg muscle activity correlated with propulsive impulses across all subjects, but not within the severe group exclusively.

Conclusions: Paretic propulsion is strongly associated with increased plantarflexor activity and also negatively associated with increased leg flexor activity, especially in the severe hemiparesis group. These results suggest that exaggerated flexor muscle activity may counteract the effects of the plantarflexors by offloading the leg and interfering with the limb's ability to generate appropriate AP ground reaction forces. There is also evidence for specific relationships between paretic braking and nonparetic propulsive forces and changes in timing of muscle activation.

Fig 1

Bins associated with the AP ground reaction forces of the paretic leg are illustrated (solid line). The gray shaded regions represent double-support phases. Abbreviations: NHS, nonparetic heel-strike; NTO, nonparetic toe-off; PHS, paretic heel-strike; PTO, paretic toe-off.

Fig 2

AP ground reaction force, impulse, and bin electromyographic data for a representative subject classified as mildly hemiparetic with a self-selected walking speed of 1.26m/s. Net bin impulses are similar, as is the duration of stance spent on each leg. Vertical lines in the ground reaction force plot indicate bin boundaries. Note that bins 1 through 4 correspond to the stance phase only. The units for the AP impulse (AP Imp) and bin electromyography are percentage of body weight (BW) × seconds and percentage of total integrated electromyography, respectively. Abbreviations: BF, biceps femoris; GM, gluteus medius; MG, medial gastrocnemius; RF, rectus femoris; SM, semimembranosus; SO, soleus; TA, tibialis anterior; VL, vastus lateralis.

Fig 3

AP ground reaction force, bin impulse, and bin electromyographic data for a representative subject classified as moderately hemiparetic with a self-selected walking speed of .73m/s. Net bin impulses are asymmetrical, however this subject generated some paretic propulsion in bin 4. Vertical lines in the ground reaction force plot indicate bin boundaries. Note that bins 1 through 4 correspond to the stance phase only. The units for the AP impulse (AP Imp) and bin electromyography are percentage of body weight × seconds and percentage of total integrated electromyography, respectively. Abbreviations: see fig 2 legend.

Fig 4

AP ground reaction force, bin impulse, and bin electromyographic data for a subject classified as severely hemiparetic with a self-selected walking speed of .44m/s. Net bin impulses are asymmetrical, with the paretic leg primarily generating braking and the nonparetic leg primarily generating propulsion. Vertical lines in the ground reaction force plot indicate bin boundaries. Note that bins 1 through 4 correspond to the stance phase only. The units for the AP impulse (AP Imp) and bin electromyography are percentage of body weight × seconds and percentage of total integrated electromyography, respectively. Abbreviations: see fig 2 legend.