Background and purpose: The Muscle Shortening Maneuver (MSM) is derived from Feldman's λ model of motor control, and seems to induce a more balanced agonist- antagonist-muscular action. The hypothesized mechanism of action is a modulation of the Tonic Stretch Reflex Threshold (TSRT). We designed a pilot, randomized trial aimed to explore the mechanisms of action of the technique. An ancillary objective was to research the implementation of the MSM as a stroke rehabilitation intervention.
Methods: A sample of 10 participants with chronic stroke was enrolled and randomly assigned to MSM (n, 5) or conventional physical therapy (CPT) (n, 5) treatments. The TSRTs were assessed by the Montreal Spasticity Measure device. A selection of clinical and instrumental outcome measures was taken to investigate function and activity levels. Data were collected at baseline, end-of-treatment, and one month after the end-of-treatment.
Results: No adverse events were observed. In both between- and within-group post-treatment assessments, in the affected ankle the MSM group showed decreased TSRTs of the plantar flexor, increased strength of the dorsiflexor and active range of motion; also, the time needed to perform the Timed Up and Go test decreased. No changes were evident across assessments in the CPT group.
Discussion and conclusions: The MSM seems able to modulate the TSRTs in individuals with stroke. Although with the limitations due to the pilot design, the variation in participants' responses appear to be promising. Many methodological issues have to be clarified and specified conceiving the progression toward a confirmatory trial.
Keywords: Stroke; motor control; muscle shortening maneuver; plantar flexors muscles; rehabilitation; spasticity; tonic stretch reflex threshold.