Reperfusion response changes induced by repeated, sustained contractions in normal human masseter muscle

Area of Science:

• Physiology
• Exercise Physiology
• Muscle Physiology

Background:

• The masseter muscle is crucial for mastication.
• Understanding its blood flow dynamics during sustained contractions is important for diagnosing and treating muscle fatigue and pain.

Purpose of the Study:

• To evaluate the intramuscular reperfusion response characteristics after repeated isometric contractions in the human masseter muscle.
• To investigate changes in blood volume and vasodilatory responses with sustained effort.

Main Methods:

• Near-infrared spectroscopy (NIRS) was used to quantify intramuscular blood volume (total hemoglobin concentration).
• Electromyography (EMG) and bite force were recorded simultaneously.
• Healthy volunteers performed repeated maximal voluntary contraction (MVC) tasks.

Main Results:

• The trough-to-peak difference in hemoglobin concentration during the second contraction task was significantly smaller than the first.
• This indicates a diminished post-contraction reperfusion response with repeated sustained effort.
• Masseter muscle blood volume recovery was reduced after the second contraction task.

Conclusions:

• Sustained isometric contractions lead to diminished vasodilatory reperfusion responses in the human masseter.
• These findings suggest a progressive desensitization of the vasodilatory system with repeated muscle effort.
• This could have implications for understanding muscle fatigue and recovery mechanisms.