EFFECTS OF MUSCLE SHORTENING MANOEUVRE ON MOTOR CONTROL: A CLINICAL MODEL

The Muscle Shortening Maneuver (MSM), a physiotherapy approach, was introduced by Grimaldi et al. in the eighties and is derived from Feldman’s λ model of motor control (Melchiorre, 2014). In the λ model the regulation of the stretch reflex threshold, that is the lower muscle length or joint angle at which motoneuronal recruitment occurs, plays a pivotal role (Feldman, 1995; Latash, 2010). The dynamic stretch reflex threshold (DSRT) is influenced by stretch speed. The tonic stretch reflex threshold (TSRT) represents the specific value of the DSRT at zero velocity. DSRTs and TSRTs are expressed in relation to the configuration of the joints, within a body frame of reference (FR) [4]. MSM is non-invasive and free of side effects, and is locally used in clinical practice (Ferrarello, 2021); it consists of two essential simultaneously applied elements: a muscle shortening and a solicitation in traction. A physiotherapist applies a series of fast accelerations to a skeletal segment (e.g., the foot) in the presence of forces acting in the opposite direction (added mass), thus producing a tensile stress. MSM provokes a dynamic lengthening associated with sudden shortening of the agonist and antagonist muscles. Tissue deformation stimulates the muscle spindles, with an enrolment of motor units and an attempt to produce muscle tension. However, the development of tension is prevented by the sudden shortening of the muscle due to the therapeutic maneuver. It is widely used in clinical practice but with little scientific evidence. The aim of the thesis is to investigate the neurophysiological mechanisms underlying it. With these assumptions, an intervention study on patients with chronic stroke in which, through the use of a portable device, it has been possible to use the TSRTs as an objective outcome measure, has been designed. In order to test this protocol and before embarking on a real randomized clinical trial, a pilot study was performed. Despite the limitations of this type of study design do not allow to make assumptions on the real efficacy of the treatment, it was already possible to identify real physiological changes in patients. Moreover, the pilot study has been useful to detect the criticalities of the original research project and therefore to make changes to support a better execution of the future trial. In the meanwhile a retrospective analysis which led to a re-elaboration of data obtained in the recent past was conducted. In particular, in a case series of 9 subjects with infantile cerebral palsy, the evaluation of objective outcomes (muscle strength, range of motion) is found for the first time in relation to functional outcomes measured by scales (Selective Motor Control Scale, Physician Rating Scale). Despite the many limitations that a series of cases with such a small sample can have, it was considered important to proceed with a more in-depth analysis of the data obtained in order to reflect on the possible presence of strong outcomes that would really change the physiological and functional characteristics of the subjects. This would have allowed to lay the foundations for future work to better investigate the effects of MSM on movement control in individuals with central nervous system injury. The effects of the maneuver were also investigated in terms of pure electromyographic activity in a pediatric patient with post-surgical peroneal nerve resection. Also in this patient it was possible to find a clear modification of the outcomes in question with a strong reduction in clinical and functional findings and greater daily autonomy in the activities of life. Obviously, the limits of the observation of a single case are evident and the results cannot be considered as evidence of efficacy but it is considered important, even in this case, to detect the presence of hard outcomes of the therapeutic path. Furthermore, the literature on MSM shows the possible effects of this type of treatment also on orthopedic injuries. In particular, two articles by Melchiorre et al. showed that this type of intervention seems effective on patients with Shoulder Impingement Syndrome (SIS) in terms of morpho-structural changes in the musculotendinous compartment of the joint, detectable by ultrasound, and of increased strength and pain relief. This protocol was selected for the design and execution of a study on subjects with SIS from a population that practices an overhead sport, water polo. In this randomized and controlled study, it was possible to observe objective and immediate changes in the musculotendinous components in correspondence with a significant decrease of pain. In conclusion, the results of these studies seem to highlight a real effect of MSM on motor control understood as modulation of TSRT, in the perspective of Feldman's threshold referent control theory.