Acute hypoxia limits endurance but does not affect muscle contractile properties

Area of Science:

• Exercise Physiology
• Skeletal Muscle Physiology
• Hypoxia Research

Background:

• Skeletal muscle dysfunction is known in vitro under acute hypoxia.
• Limited understanding exists regarding in vivo effects of acute hypoxia on muscle function.
• Hypoxemia can occur in various physiological and pathological conditions.

Purpose of the Study:

• To investigate the in vivo effects of acute hypoxia on isometric contractile properties and fatigue resistance of human skeletal muscle.
• To differentiate between voluntary and electrically evoked contractions under hypoxic conditions.
• To assess the impact of varying contraction intensities on endurance during hypoxia.

Main Methods:

• 10 healthy male subjects participated.
• Isometric contractile properties and fatigue resistance of quadriceps muscle were measured.
• Measurements were taken during both normoxia and acute hypoxia using voluntary and electrically evoked contractions.
• Oxygen saturation (SaO(2)) was monitored.

Main Results:

• Oxygen saturation significantly decreased during hypoxia (96.9% to 79.9%).
• Maximal voluntary contraction (MVC), force-frequency relationships, and contraction/relaxation times were not significantly altered by hypoxia.
• Endurance time for sustained 30% MVC contractions was reduced under hypoxia (P < 0.05).
• Endurance for 70% MVC and fatigue from electrically evoked contractions remained unchanged.

Conclusions:

• Acute hypoxia does not significantly impair in vivo skeletal muscle contractile properties.
• Reduced endurance during low-level sustained voluntary contractions is observed under acute hypoxia.
• Skeletal muscle dysfunction in prolonged hypoxemia is likely not solely due to acute hypoxic effects, excluding limited endurance.