Bilateral Strength Deficit Is Not Neural in Origin; Rather Due to Dynamometer Mechanical Configuration

Area of Science:

• Biomechanics
• Human Physiology
• Sports Science

Background:

• The bilateral strength deficit is a phenomenon where unilateral muscle force exceeds bilateral force.
• The underlying mechanisms of this deficit remain unclear.
• The contribution of body adjustments to force production has been minimally explored.

Purpose of the Study:

• To investigate the role of body adjustments in the bilateral strength deficit.
• To evaluate plantar-flexor force production using a novel dynamometer.
• To differentiate torque from body adjustments versus direct ankle torque.

Main Methods:

• Twenty healthy males performed unilateral and bilateral maximal voluntary isometric plantar-flexion contractions.
• A specialized dynamometer allowed for two configurations: 'locked-unit' (including body adjustments) and 'open-unit' (excluding body adjustments).
• Electromyographic activity of agonist muscles was measured.

Main Results:

• A significant bilateral strength deficit was observed in the locked-unit configuration (p = 0.01).
• The deficit was not significant in the open-unit configuration (p = 0.07).
• Unilateral torque was greater in the locked-unit than the open-unit (p<0.001), attributed to body adjustments as muscle activation did not differ.

Conclusions:

• The mechanical setup of the dynamometer, specifically the inclusion or exclusion of body adjustments, influences the observation of the bilateral strength deficit.
• Body adjustments contribute additional torque during unilateral contractions, potentially explaining the bilateral strength deficit.
• Future research should consider the impact of body mechanics on force production.