Sensorimotor Delays Are Related to Gait Kinetics in Persons with Multiple Sclerosis

Background: Gait and balance, critical elements in independent living and quality of life, are severely impaired in persons with multiple sclerosis (MS). Gait analyses of persons with MS reveal abnormalities in speed, stride length, cadence, double support time, swing time, and significantly altered joint kinetics. The causes of gait dysfunction in persons with MS are complex and incompletely understood but factors contributing may include slowed spinal somatosensory conduction and abnormal sensorimotor control. 

Objectives: The purpose of this study was to examine the relationship between neural control of muscle activation, as represented by sensorimotor delays, and gait mechanics in persons with MS.

Methods: Thirteen persons with MS (45.8±8.5 yrs, EDSS 2.3±1.3) participated. Gait kinematics and kinetics were measured bilaterally during overground walking at self-selected pace. Next, sensorimotor delays were measured bilaterally with EMG as subjects stood on a translating surface (6 cm at 15 cm/s). The sensorimotor delay was defined as the time, in milliseconds (MS), between the onset of the surface translation and the first detectable firing of either the tibialis anterior (response to forward translation) or the gastrocnemius (response to backward translation). Subjects performed three trials each of forward and backward translation. To examine the relationship between sensorimotor delays and joint kinetics (ankle plantarflexion moment and dorsiflexion moment during the stance phase), Spearman correlations were used.

Results: Mean sensorimotor delay of the gastrocnemius was 143.6 ± 30.7 ms and of the tibialis anterior was 127.1 ± 27.4 ms. There was a significant relationship between the sensorimotor delay of the tibialis anterior and both the dorsiflexor joint torque (ρ= -0.579, p=0.003) and the plantarflexor joint torque (ρ= 0.441, p=0.031) during the stance phase. The sensorimotor delay of the gastrocnemius did not correlate with dorsiflexor (ρ= -0.225, p=0.29) or plantarflexor (ρ=0.90, p=0.65) torque.

Conclusions: These results indicate that in persons with MS, sensorimotor delays are strongly related to deficits in dorsiflexor and plantarflexor torque at the ankle during stance. These findings indicate that it is likely not only strength deficits of the muscles of the lower limbs which contribute to changes in gait kinetics in persons with MS. Instead, delays in somatosensory feedback and motor responses in persons with MS directly contribute to changes in gait kinetics.