Short-Latency Stretch Reflexes Do Not Contribute to Premature Calf Muscle Activity During the Stance Phase of Gait in Spastic Patients

Objective: To identify whether a relationship exists between stretch and activity of the calf muscles during the stance phase of gait in patients with upper motor neuron syndrome (UMNS), while taking into account the physiologic phase shift between these entities. Design: Survey. Setting: Ambulatory care and general community. Participants: Patients with UMNS (n=15; 9 patients with stroke, 6 patients with hereditary spastic paraparesis) with premature calf muscle activity during the stance phase of gait and healthy controls (n=13). Interventions: Not applicable. Main Outcome Measure: Timing of optimal association (phase shift) between the lengthening velocity of the gastrocnemius muscle and its electromyographic activity as revealed by cross-correlation analyses. Results: Although premature calf muscle activity was evident in the patient groups, the phase shift between calf muscle stretch and its activity did not correspond with the monosynaptic stretch reflex latency (40- to 80-ms time window). However, there was a main effect of group on the phase shifts (F-3.33=3.23, P=.035). Post hoc analysis revealed that in the paretic leg of stroke patients, the electromyographic activity preceded the lengthening velocity by 9 +/- 54ms, whereas in the control group, the electromyographic activity followed the pattern of the muscle-lengthening velocity with a delay of 61 +/- 54ms (P=.029). Conclusions: Short-latency stretch reflexes do not significantly contribute to premature calf muscle activity in the stance phase of (spastic) gait. This notion questions the validity of the clinical assessment of hyperreflexia and clonus of the calf as a predictor of calf muscle spasticity during gait.