Impaired stretch reflex and joint torque modulation during spastic gait in multiple sclerosis patients

Abstract

The modulation of the short latency stretch reflex of the soleus muscle during walking was investigated in seven spastic multiple sclerosis (MS) patients and nine healthy control subjects. Ankle joint stretches were applied by a system which can rotate that ankle joint in any phase of the step cycle during treadmill walking. The torque related to the muscle fibres contracting prior to the stretch and the passive tissues around the ankle joint were measured as the "non-reflex torque". At the same time the short latency stretch reflex-mediated EMG response was measured. The findings show that the stretch reflex modulation was impaired in spastic patients during walking. The stretch reflex modulation was quantified by a modulation index of an average 50% (range -5 to 100%) in the patients and 93% (78-100%) in the control subjects (P < 0.05). The passive stiffness of the ankle joint was at the same time increased in the patients (P < 0.05). It is proposed that the impaired modulation of the stretch reflex along with increased ankle joint stiffness contribute to the impaired walking ability in spastic MS patients.

Sensory feedback to ankle plantar flexors is not exaggerated during gait in spastic hemiplegic children with cerebral palsy

“…The observed pattern of EMG responses to both stretch and shortening of the ankle plantar flexors in the gait cycle closely resembles the responses observed in adults (Sinkjaer et al 1996;Toft et al 1991). The initial response to stretch was seen at a peak latency of 39.2 ms, which compares to the 57-62 ms observed by Toft et al (1991) and the 54 ms observed by Sinkjaer et al (1996) for the M1 response. With an average height of 143.3 cm in the children and an average height of 180 cm in adult Danish men, this latency difference is accounted for by the shorter conduction path in the children.…”

“…We instead chose to relate all reflex and unload measurements to the background EMG activity measured at the time of perturbation in control steps, similar to what has been done in previous studies (Hodapp et al 2007a;Sinkjaer et al 1996).…”

“…These peaks likely correspond to the M1, M2, and M3 reflex responses described in adult subjects (Sinkjaer et al 1996;Toft et al 1991). The M1 response was observed in 33 of the control children (80.5%) and in all of the children with CP (Fig.…”

“…From experiments in adults there is also reason to question the functional significance of increased stretch reflex activity measures at rest in spastic patients (Dietz and Sinkjaer 2007;Ibrahim et al 1993). A number of studies have demonstrated that hyperexcitable stretch reflexes in spastic patients are not manifest during voluntary movement including gait (Dietz and Sinkjaer 2007;Schindler-Ivens et al 2008;Sinkjaer et al 1996). Most recently, Marsden and colleagues (Marsden et al 2012) argued that muscle paresis and passive stiffness, rather that spasticity, are the main determinants of impaired movement in the knee joint during gait in patients with spastic paraparesis.…”

“…This was the purpose of the present study using the technique developed by Sinkjaer et al (1996). They demonstrated that it is possible to elicit stretch reflexes in ankle muscles during gait in adults with a portable stretching device and that adults with spasticity have increased EMG stretch-mediated reflex activity in the stance phase of walking (Mazzaro et al 2007;Sinkjaer et al 1996). Eliciting stretch reflex activity by an external perturbation in this way does not provide evidence of the ongoing sensory feedback contribution to the EMG activity and thus the functional contribution of the stretch reflex circuitry to the muscle activity.…”