Soleus muscle electromyographic activity and ankle dorsiflexion range of motion during four stretching procedures

Abstract

Volitional muscle contractions are used frequently in some combination with muscle stretching to promote muscle relaxation and to increase range of motion. In this study, muscle lengthening procedures were evaluated in the ankle plantar flexors. Four soleus muscle stretching procedures--static stretch (SS), hold relax (HR) (isometric plantar flexor contraction before stretch), agonist contract (AC) (dorsiflexor contraction assisting stretch), and hold relax-agonist contraction (HR-AC)--were performed in the sagittal plane by 12 physically active adults. The dorsiflexion angle, soleus muscle electromyogram, and soleus muscle motoneuron excitability as determined by the Hoffmann-reflex (H-reflex) amplitude were measured throughout the duration of each stretch. The range of dorsiflexion achieved at the end of the stretch did not differ significantly between stretching procedures, although in 8 of the 12 subjects and in the subject group as a whole, the AC and HR-AC procedures were associated with higher levels of soleus muscle EMG than the levels in the SS and HR procedures (p less than .01). The H-reflex amplitudes during the AC and HR-AC procedures were smaller than the amplitudes during the SS and HR procedures (p less than .001), suggesting the possibility of reciprocal inhibition during the agonist contraction. Increased tonic EMG levels produced by input from other neural pathways affecting alpha motoneurons in the AC and HR-AC procedures may have masked this inhibitory reflex. In healthy adults, a complicated procedure, involving muscle contractions for decreasing active resistance to stretch, may be unnecessary because active resistance to stretch is minimal and muscle relaxation during stretch appears to have little or no direct effect on the ROM achieved.