Electromyographic activity while performing the anti-G straining maneuver during high sustained acceleration.

Area of Science:

• Aerospace Medicine
• Human Physiology
• Biomechanical Engineering

Background:

• High sustained acceleration (+Gz) poses significant physiological stress, particularly in aviation and spaceflight.
• The anti-G straining maneuver (AGSM) is crucial for mitigating G-force effects by increasing intrathoracic pressure.
• Understanding muscle activation patterns during AGSM is vital for optimizing pilot protection and performance.

Purpose of the Study:

• To quantify muscle activity during the AGSM under high +Gz acceleration.
• To investigate changes in electromyography (EMG) amplitude and frequency in key muscle groups.
• To determine if AGSM performance leads to muscular fatigue at the motor unit level.

Main Methods:

• Ten male subjects were exposed to 6 +Gz using a rapid onset rate centrifuge.
• Surface EMG was recorded from trunk (erector spinae, external oblique) and lower extremity muscles (bicep femoris, vastus lateralis, lateral gastrocnemius).
• Normalized root-mean squares (RMS) and mean power frequency (MPF) were analyzed using ANOVA.

Main Results:

• Mean EMG amplitude significantly decreased by 35.40% during AGSM.
• Lower extremity muscle EMG amplitude decreased substantially (61.45%), while trunk muscle amplitude showed a minor decrease (3.45%).
• No significant changes were observed in the mean power frequency (MPF), indicating no muscle fatigue.

Conclusions:

• AGSM performance under high +Gz results in reduced motor unit recruitment in lower extremity muscles.
• The AGSM effectively reduces muscle activation demands without inducing muscular fatigue.
• Findings suggest that AGSM efficacy is maintained through neural adaptation rather than muscular exertion.