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Bilateral deficit and EMG activity during explosive lower limb contractions against different overloads
Enrico Rejc1, Stefano Lazzer, Guglielmo Antonutto
1Department of Biomedical Sciences and Technologies, University of Udine, Udine, Italy. enrico.rejc@uniud.it
European Journal of Applied Physiology
|September 22, 2009
Summary
Bilateral deficit (BLD) occurs during explosive lower limb contractions, with reduced force and power compared to single limb efforts. This phenomenon is primarily attributed to altered muscle coordination, not solely neural drive or force-velocity changes.
Area of Science:
- Biomechanics
- Human Physiology
- Sports Science
Background:
- The bilateral deficit (BLD) describes the phenomenon where the force generated by two limbs contracting together is less than the sum of the forces generated by each limb individually.
- While BLD is well-documented in maximal voluntary contractions, its occurrence and underlying mechanisms during explosive, dynamic movements, particularly in the lower limbs, remain less understood.
Purpose of the Study:
- To investigate the presence of bilateral deficit (BLD) during explosive lower limb contractions.
- To determine if BLD during these contractions is associated with reduced neural drive, altered muscle coordination, or changes in the force-velocity (F-v) relationship.
- To elucidate the primary contributing factors to BLD in explosive lower limb movements.
Main Methods:
- Ten volunteers performed maximal explosive efforts on a sledge ergometer using both lower limbs (BL) and single limbs (ML) against varying overloads.
- Measurements included peak force, peak power, peak velocity, and electromyography (EMG) of key lower limb muscles (vastus lateralis, rectus femoris, biceps femoris, gastrocnemius medialis).
- Analysis focused on comparing force, power, EMG activity, intermuscular coordination, and F-v relationships between BL and ML conditions.
Main Results:
- Significantly lower peak force and peak power were observed during BL contractions compared to ML contractions for both limbs.
- Lower integrated EMG (iEMG) amplitudes were recorded for the vastus lateralis and rectus femoris during BL compared to ML contractions.
- Analysis revealed poorer coordination among the tested muscles during BL and distinct F-v curves, indicating reduced force and power output at given velocities in BL conditions.
Conclusions:
- Bilateral deficit (BLD) is present during explosive lower limb contractions.
- The primary factor contributing to BLD in this context appears to be altered intermuscular coordination rather than solely a reduction in neural drive or changes in the muscle's intrinsic force-velocity characteristics.
