Effects of Different Isometric Exercise Modalities on Microvascular and Metabolic Function.

Area of Science:

• Exercise Physiology
• Muscle Physiology
• Biomedical Engineering

Background:

• Muscle oxygenation (SmO₂) dynamics and microvascular function are crucial for understanding exercise performance and fatigue.
• Near-infrared spectroscopy (NIRS) offers a non-invasive method to assess these physiological parameters during exercise.

Purpose of the Study:

• To compare microvascular function, SmO₂ dynamics, and fatigability during sustained isometric forearm flexion under constant torque (CT) versus rating of perceived exertion (RPE)-matched conditions.
• To investigate the effects of different exercise protocols on muscle oxygenation and microvascular recovery.

Main Methods:

• Thirteen healthy males performed sustained isometric forearm flexion under two conditions: RPE-Clamp (RPE level 3) and CT (matched to initial RPE-Clamp torque).
• NIRS was used to measure SmO₂, while maximal voluntary isometric contractions (MVIC) and time to task failure (TTF) assessed fatigability.
• Vascular occlusion tests (VOT) evaluated microvascular function pre- and post-exercise.

Main Results:

• CT resulted in significantly greater performance fatigability than RPE-Clamp, despite similar TTF.
• SmO₂ dynamics differed, with CT showing decreases in early/late phases and RPE-Clamp showing increases in mid-phases.
• Post-exercise VOT revealed reduced desaturation rates, increased tissue hypoxia, and enhanced microvascular reactivity for both conditions, with greater peak re-saturation in CT.

Conclusions:

• Both CT and RPE-Clamp protocols enhance microvascular reactivity.
• CT elicits greater fatigability and muscle desaturation compared to RPE-Clamp.
• Prolonged isometric exercise and associated hypoxic stress may contribute to improved post-exercise microvascular function and reduced desaturation rates.