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Bilateral and unilateral contractions: possible differences in maximal voluntary force
1School of Kinesiology, Faculty of Health Sciences, University of Western Ontario, London, Ontario, Canada N6G 2M3.
Summary
The bilateral deficit (BLD), where two-limb force is less than summed single-limb force, is an unstable phenomenon. Its presence depends on movement type and neural drive variations.
Area of Science:
- Neuromuscular Physiology
- Motor Control
- Human Movement Science
Background:
- The bilateral deficit (BLD) describes a phenomenon where the force generated by simultaneous bilateral limb contractions is less than the sum of forces from individual unilateral contractions.
- Significant debate exists in the literature regarding the presence and consistency of the BLD, particularly contrasting findings from dynamic versus isometric movements.
- Understanding the BLD may offer insights into complex neuromuscular control mechanisms and interlimb coordination.
Purpose of the Study:
- To critically examine the concept of the bilateral deficit (BLD) and its variability in the scientific literature.
- To propose that the BLD is an unstable phenomenon contingent on the specific movement context.
- To investigate the potential influence of descending neural drive modulation on the manifestation of the BLD.
Main Methods:
- Review and synthesis of existing literature on bilateral force production and the bilateral deficit.
- Categorization of studies based on movement type (dynamic vs. isometric) and experimental conditions.
- Theoretical analysis of neuromuscular control pathways and descending motor command variability.
Main Results:
- Dynamic movement studies frequently report a bilateral deficit, while isometric studies present more controversial and varied results.
- The presence and magnitude of the BLD appear to be influenced by the type of contraction and task demands.
- Variations in descending neural drive to motor neurons are suggested as a key factor influencing the bilateral deficit.
Conclusions:
- The bilateral deficit is not a universal or stable phenomenon but rather context-dependent.
- The manifestation of the BLD is likely influenced by subtle alterations in neural drive originating from the central nervous system.
- Further research should carefully consider movement type and neural factors when investigating the bilateral deficit.