Trunk muscle amplitude-force relationship is only quantitatively influenced by control strategy

Area of Science:

• Biomechanics
• Human Physiology
• Neuromuscular Control

Background:

• The relationship between surface electromyography (SEMG) amplitude and force is non-linear for abdominal muscles and linear for back muscles.
• Trunk muscle stress is influenced by control strategies, with posture-controlled tasks showing higher SEMG amplitudes than force-controlled tasks.

Purpose of the Study:

• To investigate whether different trunk muscle control strategies quantitatively or qualitatively alter the SEMG amplitude-force relationship.
• To compare SEMG responses between posture-controlled and force-controlled tasks in healthy adults.

Main Methods:

• 39 healthy subjects performed isometric trunk flexion and extension under posture-controlled and force-controlled conditions.
• Surface electromyography (SEMG) was recorded from five trunk muscles.
• SEMG data were normalized to maximum voluntary contractions (MVC) and maximum values within each condition.

Main Results:

• MVC-normalized SEMG amplitudes were higher for abdominal muscles in posture-controlled conditions, irrespective of sex.
• Back muscles' MVC-normalized SEMG amplitudes were not affected by control strategy.
• Maximum normalized SEMG amplitudes were not systematically influenced by the control strategy across all trunk muscles.

Conclusions:

• The SEMG amplitude-force relationship in trunk muscles is specific to the muscle group and exercise type.
• Control strategy quantitatively alters the SEMG amplitude-force relationship for abdominal muscles, but not for back muscles.