Abstract
Disinhibition of reflexes is a problem amongst spastic patients, for it limits a smooth and efficient execution of motor functions during gait. Treadmill belt accelerations may potentially be used to measure reflexes during walking, i.e. by dorsal flexing the ankle and stretching the calf muscles, while decelerations show the modulation of reflexes during a reduction of sensory feedback. The aim of the current study was to examine if belt accelerations and decelerations of different intensities applied during the stance phase of treadmill walking can evoke reflexes in the gastrocnemius, soleus and tibialis anterior in healthy subjects. Muscle electromyography and joint kinematics were measured in 10 subjects. To determine whether stretch reflexes occurred, we assessed modelled musculo-tendon length and stretch velocity, the amount of muscle activity, as well as the incidence of bursts or depressions in muscle activity with their time delays, and co-contraction between agonist and antagonist muscle. Although the effect on the ankle angle was small with 2.8±1.0°, the perturbations caused clear changes in muscle length and stretch velocity relative to unperturbed walking. Stretched muscles showed an increasing incidence of bursts in muscle activity, which occurred after a reasonable electrophysiological time delay (163–191 ms). Their amplitude was related to the muscle stretch velocity and not related to co-contraction of the antagonist muscle. These effects increased with perturbation intensity. Shortened muscles showed opposite effects, with a depression in muscle activity of the calf muscles. The perturbations only slightly affected the spatio-temporal parameters, indicating that normal walking was retained. Thus, our findings showed that treadmill perturbations can evoke reflexes in the calf muscles and tibialis anterior. This comprehensive study could form the basis for clinical implementation of treadmill perturbations to functionally measure reflexes during treadmill-based clinical gait analysis.
Highlights
Spasticity is one of several problems regularly faced by patients with cerebral palsy, spinal cord injury, stroke or multiple sclerosis
Since the measured muscle response is dependent on the perturbation, the characteristics of the perturbations are first precisely described in Fig 2 and Table 1
Our findings show that belt speed perturbations during walking on a treadmill can evoke muscle reflexes in the calf muscles and tibialis anterior (TA) in healthy subjects
Summary
Spasticity is one of several problems regularly faced by patients with cerebral palsy, spinal cord injury, stroke or multiple sclerosis. It is traditionally defined as a velocity-dependent increase in muscle tone due to hyper excitability of the stretch reflexes [1]. Different treatments are available to reduce the effects of spasticity, such as chemical denervation of muscles by botulinum toxin injections to weaken the muscles or reduction of dorsal nerve roots by rizhotomy to reduce sensory afferents. To select a treatment for a patient, clinicians typically rely on unloaded and passive stretch measurements based on imposed movement of one joint, while asking the patient to relax. It would be much more meaningful to be able to measure reflex activity during gait
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