Synergistic difference in the effect of stretching on electromechanical delay components

Area of Science:

• Biomechanics
• Human Physiology
• Exercise Science

Background:

• Electromechanical delay (EMD) and relaxation EMD (R-EMD) are crucial for understanding muscle function.
• Passive stretching is a common intervention, but its differential effects on synergistic muscles are not fully understood.
• Simultaneous measurement of electromyographic, mechanomyographic, and force signals provides comprehensive data on muscle activation and contraction dynamics.

Purpose of the Study:

• To investigate the synergistic differences in the effects of passive stretching on EMD and its components.
• To analyze the impact of stretching on the electrochemical and mechanical aspects of EMD and R-EMD in specific plantar flexor muscles.
• To explore the relationship between joint passive stiffness and EMD/R-EMD parameters.

Main Methods:

• Twenty-six healthy men underwent passive stretching of the plantar flexors.
• Electromyographic, mechanomyographic, and force signals were recorded simultaneously.
• EMD, R-EMD, and joint passive stiffness were measured before and after stretching in gastrocnemius medialis, lateralis, and soleus muscles during supramaximal motor point stimulation.

Main Results:

• Stretching reduced joint passive stiffness and lengthened both electrochemical and mechanical EMD.
• The mechanical components of R-EMD were more affected in gastrocnemius medialis and lateralis (21-22% increase) than in soleus (12% increase).
• Significant negative correlations were observed between joint passive stiffness and the mechanical components of EMD and R-EMD across all muscles.

Conclusions:

• Passive stretching of the plantar flexors impacts synergistic muscles unequally, with gastrocnemius medialis and lateralis exhibiting greater alterations in EMD and R-EMD.
• The findings highlight the importance of considering muscle-specific responses to stretching interventions.
• Further research is warranted to elucidate the mechanical adaptations induced by passive stretching in synergistic muscle groups.