Effects of post activation potentiation on electromechanical delay

Area of Science:

• Biomechanics
• Human Physiology
• Sports Science

Background:

• Electromechanical delay (EMD) is influenced by both contractile and tensile muscle properties.
• EMD has been utilized as an indirect measure of muscle tendon stiffness, particularly in response to stretching and training.
• The influence of contractile property changes on EMD, independent of passive stiffness alterations, requires further investigation.

Purpose of the Study:

• To determine if contractile properties, modulated by a 6-second maximum voluntary isometric contraction (MVIC), affect EMD.
• To assess whether these contractile changes impact passive muscle tendon stiffness or stiffness index.
• To investigate the acute effects of MVIC on EMD and contractile properties.

Main Methods:

• Plantar flexor twitches were evoked using tibial nerve electrical stimulation in eight male sprinters.
• EMD, twitch contractile properties, and SOLM-Wave were measured before and after a 6-second MVIC.
• Passive muscle tendon stiffness and stiffness index were quantified through controlled passive dorsiflexion torque-angle relationships.

Main Results:

• EMD was reduced by up to 11.56% post-MVIC and remained depressed for 60 seconds.
• Peak twitch torque and rate of torque development increased significantly (up to 119.41% and 116.06%, respectively).
• No significant changes were observed in passive muscle tendon stiffness or stiffness index.

Conclusions:

• A conditioning MVIC acutely enhances muscle contractile properties, leading to a significant reduction in EMD.
• These EMD reductions occur without concomitant changes in passive muscle tendon stiffness or stiffness index.
• Caution is advised when interpreting EMD as a direct proxy for muscle tendon stiffness, as contractile factors play a significant role.