Transient Increase in Cortical Excitability Following Static Stretching of Plantar Flexor Muscles.

Francesco Budini,Monica Christova,Dietmar Rafolt,Paul Kressnik,Eugen Gallasch,Markus Tilp

doi:10.3389/fphys.2018.00530

Abstract

Spinal excitability in humans is inhibited by both passively holding a static position with the muscle lengthened (static stretching) and by a single non-active lengthening movement. However, whilst immediately after a passive lengthening movement the inhibition persists for several seconds, there seem to be an immediate recovery following static stretching. This result is counter intuitive and could be attributed to methodological procedures. Indeed, differently to what has been done until now, in order to study whether static stretching has a transient effect on the neuromuscular pathway, the procedure should be repeated many times and measurements collected at different time points after stretching. In the present study we repeated 60 times 30 s static stretching of ankle plantar flexors and measured tap reflex (T-reflex), Hoffman reflex (H-reflex), and motor evoked potentials (MEPs) from the Soleus muscle at several time points, starting from immediately after until 30 s following the procedure. T-reflex was strongly inhibited (range 31–91%, p = 0.005) and the inhibition persisted for 30 s showing a slow recovery (r = 0.541, p = 0.037). H-reflex was not affected by the procedure. Stretching increased the size of the MEPs (p < 0.0001), differences at times 0 and 2 s after stretching (p = 0.015 and p = 0.047, respectively). These results confirm that static stretching reduces muscle spindle sensitivity. Moreover it is suggested that post-activation depression of Ia afferents, which is commonly considered the cause of H-reflex depression during both dorsiflexion and static stretching, vanished immediately following stretching or is counteracted by an increased corticospinal excitability.

Highlights

Conditioning a muscle by means of stretching induces changes in muscle compliancy (Konrad et al, 2017), and in discharge and sensitivity of muscle spindles (Gregory et al, 1987), excitability of spinal pathways (Budini et al, 2017), and cortical excitability (Stuart et al, 2002)
Following stretching there was a considerable reduction in reflex amplitude in respect to baseline values, with significantly different group average T-reflex values ranging from 0.85 and 1.37% of the Mmax
The present experiment confirms some of the known effects of muscle stretching on spinal reflex excitability and reveals a previously unreported effect on corticospinal excitability

Summary

Introduction

Conditioning a muscle by means of stretching induces changes in muscle compliancy (Konrad et al, 2017), and in discharge and sensitivity of muscle spindles (Gregory et al, 1987), excitability of spinal pathways (Budini et al, 2017), and cortical excitability (Stuart et al, 2002). To traditional static stretching, conditioning a muscle through a passive eccentric movement consists in either elongating the muscle a single time and returning it to its neutral anatomical position (e.g., dorsiflex the ankle joint and back) or in reaching the neutral anatomical position with an eccentric movement (starting for example with the ankle joint in plantar flexion position) Following this procedure, spinal excitability was reported to be strongly inhibited for several seconds (2–15 s) (Delwaide and Hugon, 1969; Nielsen et al, 1993, 1995; Hultborn et al, 1996; Wood et al, 1996; Voigt and Sinkjær, 1998)

Objectives

Results

Conclusion