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

Abstract

During maximal contractions, the sum of forces exerted by homonymous muscles unilaterally is typically higher than the sum of forces exerted by the same muscles bilaterally. However, the underlying mechanism(s) of this phenomenon, which is known as the bilateral strength deficit, remain equivocal. One potential factor that has received minimal attention is the contribution of body adjustments to bilateral and unilateral force production. The purpose of this study was to evaluate the plantar-flexors in an innovative dynamometer that permitted the influence of torque from body adjustments to be adapted. Participants were identically positioned between two setup configurations where torques generated from body adjustments were included within the net ankle torque (locked-unit) or independent of the ankle (open-unit). Twenty healthy adult males performed unilateral and bilateral maximal voluntary isometric plantar-flexion contractions using the dynamometer in the open and locked-unit mechanical configurations. While there was a significant bilateral strength deficit in the locked-unit (p = 0.01), it was not evident in the open-unit (p = 0.07). In the locked-unit, unilateral torque was greater than in the open-unit (p<0.001) and this was due to an additional torque from the body since the electromyographic activity of the agonist muscles did not differ between the two setups (p>0.05). This study revealed that the mechanical configuration of the dynamometer and then the body adjustments caused the observation of a bilateral strength deficit.

Bilateral Deficit During Jumping Tasks: Relationship With Speed and Change of Direction Speed Performance

“…However, speculation still exists as to the underlying mechanisms responsible for this phenomenon. Several theories have been proposed to explain the existence of the BLD, including changes in motor unit recruitment (13,20,29), the force-velocity relationship (4,15), neural mechanisms (18), limb dominance (18), training preference (i.e., bilateral over unilateral movements and vice versa) (18,34) and the ability to counter-balance and support movement (24,35). Therefore, it may be plausible to suggest that multiple mechanisms contribute to the prevalence of the BLD.…”

Muscular performance decreases with increasing complexity of resistance exercises in subjects with chronic obstructive pulmonary disease

“…In healthy controls, 1RM −leg in two‐legged leg press was 6% lower than 1RM in one‐legged leg press (though without reaching statistical significance). This phenomenon is frequently described in the literature and is coined the bilateral deficit . In contrast, in COPD, 1RM −leg in two‐legged leg press was 5% higher (non‐significant) than 1RM in one‐legged leg press, suggesting that the bilateral deficit was absent in these patients.…”

The Bilateral Limb Deficit (BLD) Phenomenon During Leg Press: An Investigation Into Central And Peripheral Factors

“…There is comparable evidence to suggest that single-jointed movements, such as knee extension, may result in a smaller bilateral de cit compared to multi-jointed movements, such as a lateralis pull-down and leg press (Janzen et al 2006). This is because multi-jointed movements tend to involve larger muscles and greater force production, thus requiring greater postural stability (Simoneau-Buessinger et al, 2015). It was determined that muscle activation of the trunk was signi cantly greater in the leg press, a multi-joint movement, compared to the knee extension and handgrip exercises, which are single-jointed movements.…”