Can Treadmill Perturbations Evoke Stretch Reflexes in the Calf Muscles?

• Published in: PloS one Vol. 10; no. 12; p. e0144815
• Main Authors: Sloot, Lizeth H., van den Noort, Josien C., van der Krogt, Marjolein M., Bruijn, Sjoerd M., Harlaar, Jaap
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 15.12.2015; Public Library of Science (PLoS)
• Subjects: Acceleration; Adult; Ankle; Biomechanics; Cerebral palsy; Contraction; Deceleration; Electromyography; Exercise Test; Feedback; Female; Fitness equipment; Flexing; Gait; Humans; Incidence; Kinematics; Kinesiology; Leg - physiology; Legs; Male; Medicine; Muscle contraction; Muscle function; Muscle, Skeletal - physiology; Muscles; Patients; Physiological aspects; Reflex, Stretch - physiology; Reflexes; Rehabilitation; Sensory feedback; Skeletal muscle; Time lag; Timing; Treadmills; Treadmills (Exercise equipment); Velocity; Walking; China
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0144815

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.